As homes get larger, and bathrooms more customized with larger and larger showers and tubs, the standard 40-gallon water heater isn't the one-size-fits-all appliance it once was.
Furthermore, as energy prices continue to rise along with the size of a home's hot water demand, the options in water heating technology have grown wide and varied. To help you select the correct water heater that both ensures you never run out, while at the same time, don't produce far more than you need, here are a few tips and techniques for selecting the right size appliance.
Since the goal is to never run out of hot water, always assume a worst-case scenario. This means delivering enough hot water based on the assumption that every tap and hot water-consuming appliance (i.e. laundry machines, dishwasher) will be used simultaneously.
With that in mind, calculate the gallons-per-minute (gpm) demand at every draw-point and fixture. To figure out the gpm-demand of any given fixture, get a one-gallon container (like a milk jug) and a watch with a minute-hand. See how long it takes to fill and the container and do the math (if the jug fills in 30-seconds, the flow-rate would be 2 gpm). For appliances like dishwashers and clothes washers, the water-consumption data will often be provided in the manufacturer's literature.
Once you've added the total gpm for all appliances, multiply by .85. Why? Your water heater will usually maintain a temperature of 120-degrees, however, you usually temper this down with a bit of cold water to about 100 degrees -- 100 degrees is about 85% of 120. Once you multiply the demand of all fixtures and appliances by .85, this is the total gpm that you need from your water heater.
For on-demand water heaters, figuring-out the size you need is pretty cut and dry. All manufacturers provide output-data (expressed in gpm) based on a specific temperature rise. The rise refers to the difference in temperature between what you'll heat the water to minus the temperature of the water as it enters the home. In many parts of the U.S., water enters the home at about 55 degrees and is heated to 120 degrees -- a rise of 75.
If the output of the on-demand water heater exceeds the demand of your home, you have a winner. In some cases, however, your demand will be larger than the output of the on-demand water heater (this is fairly common in larger homes). If this is the case, you can either use multiple on-demand water heaters or move to a large tank-type model. In most cases, it's more cost-effective to purchase a large-capacity tank versus multiple on-demand systems.
If you opt for a tank-type water heater, you'll want to refer to the appliance's "First-Hour Rating." This number basically equates to the number of gallons a water heater can provide per hour. Take this number, divide it by 60, and this the the total gpm the water heater can deliver. If the first-hour rating (divided by 60) is larger than the total gpm demand calculated for your home, the water heater should do the trick. But there's an exception.
The First-Hour Rating doesn't account for a potential "dump load." Here's what we mean. If you have a 40-gallon water heater, but have a bath tub that holds 50 gallons, there's a strong likelihod that the water heater will become depleted, unless it has a super-huge burner like those found in commercial water heaters (big bucks). So, if you have a large soaking tub, we recommend you purchase a water heater that has a capacity that's at least 1.5 times the size of the tub.
Why more? Two reasons.
First, just because the tank says 60 gallons, you don't actually get 60 gallons of hot water. As you fill the tub, emptying hot water from the tank, it gets replaced by cold water. Consequently, this cold water mixes-down the the temperature of the tanks hot water, thus diminishing the amount of total available hot water.
Second, again, we want to assume that other fixtures will be in use as you fill the big tub. By oversizing by a factor of 50 percent, we allow for extra demand.
Sizing water heaters is as much art as it is science. When in doubt, contact a qualified professional. Furthermore, by allowing an installation contractor to size the appliance for you, you're putting the liability on him (or her) instead of assuming the risk yourself.
Commercial Applications:
Commercial water heating applications can be much more varied, and sometimes requires a more sophisticated approach to calculating the correct size appliance(s). Moreover, commercial equipment can be very expensive. At the same time, water heating can represent a lrge percentage of a business' energy overhead. As a result, it is important to get it right -- the first time.
Many factors come into play in commercial water heating applications -- overall demand, time of use, energy costs, storage needs versus btu-output, etc. If you have a commercial water heating need, we highly recommend you either: 1) hire Enhanced Living to design your system, or 2) hire a mechanical engineer with specific expertise in this area.
If you have fairly generic needs and/or a small demand, use the above guidelines for residential applications, or use one of the following calculators:
Product Alert: Amtrol Boiler Mate
In the quest for a low-cost indirect water heater, many contractors and homeowners turn to Amtrol's BoilerMate. Big mistake. Not only is the BoilerMate poorly insulated -- a mere 3/4" layer of insulation -- it utilizes a finned-coil heat-exchanger.
With one notable exception*, most indirect-fired water heaters utilize one of two styles of internal heat-exchanger -- either a copper finned-tube, or a smooth steel coil.
Avoid finned-tube heat-exchangers, especially if you have relatively hard water. The problem is that minerals within the water cling easily to finned-tubes, to the point that they become coated entirely in mineral-scale. When this happens, the mineral-scale inhibits the heat-exchanger's ability to transfer heat to the stored water, causing the attached boiler to short-cycle and operate extremely inefficiently.
Think this is just theory? Think again. Below is a photograph of an eight year-old BoilerMate with its finned-tube heat-exchanger removed. The white layers of mineral scale are clearly apparent.
We discovered this gem at a client's home. While he new something was awry with his heating system, evidenced by a slow, gradual climb in heating costs, he didn't think much of the fact that his boiler would operate nearly constantly -- turning on and off, on and off, throughout the day, as the water heater struggled to make hot water.
Once replaced by a Viessmann Vitocell 100 (the original H.B. Smith boiler was also replaced with a Viessmann Vitorond 100), the improvement was immediately noticed. The new boiler/tank combo runs like a top, with a huge increase in efficiency and an abundance of hot water.
Moral of the story -- avoid finned-tube heat-exchangers. Even if you're on a tight budget, there are plenty of low-cost indirect-fired water heaters that utilize a smooth-walled steel coil.
* The notable exception is Triangle Tube's Phase III water heater, which utilizes a "tank-in-tank" design. The Phase III is a quality indirect-fired water heater -- a good choice among stainless steel tanks.
Energy Audits Get Hot..EL on Businessweek.com
Enhanced Living makes national press -- Read about Energy Audits on Businessweek.com.
Avoid whole-house humidifiers
Cold weather brings dry homes. And dry homes bring itchy skin, scratchy throats, and irritated sinuses.
To counter the effects of "dry house syndrome," the first thing homeowners and contractors often reach for is a central humidifier.
To counter the effects of "dry house syndrome," the first thing homeowners and contractors often reach for is a central humidifier.
If you happen to be an admitted germ-phobe, central humidifiers aren't for you. Think swamp-environment. That's the best way to describe the conditions inside your furnace-attached humidifier; a breeding-ground for bacteria, viruses, and molds.
If you have leaky ducts that run through an unconditioned area, such as the attic, warm "humidified" air is able to escape and condense on the cold roof-deck, causing costly moisture-damage and/or rot.If you want to maintain comfortable winter humidity levels (+-40 percent RH), here's a more "holistic" approach:
- Reduce your homes air-leaks. Cutting the homes air-infiltration rate reduces the amount of moisture that gets lost to the outside. Reducing air-leaks also reduces drafts and saves energy.
CAVEAT: In our opinion, there's no such thing as an "overtight" home -- only an underventilated one. That said, if you don't have adequate ventilation, excess moisture can be a problem in tight homes. Additionally, overtightening the home in a manner that seals-off a furnace' or water-heaters source of combustion air increase the risk of back-drafting the chimney and introducing carbon monoxide into the home. - Consider an energy-recovery ventilator (ERV). ERVs like their close-cousin, the heat-recovery ventilator (HRV), are 'balanced' ventilation systems. Conventional exhaust-only ventilators (i.e. standard bathroom fan) get their make-up air by pulling it through the cracks and leaks in the home. Not a very well-controlled method, and certainly not the best for indoor air quality.
Balanced ventilators, like ERVs and HRVs, bring fresh air into the home by way of dedicated ducts. As an added bonus, HRVs 'recover' a portion of the heat that normally gets exhausted and returns it back inside the home, a nice energy-efficiency feature. ERVs have an added-added bonus. They recover heat AND humidity and help keep clean, fresh-air circulating through the home without drying-it out in winter. Controls prevent the unit from causing excessive humidity-levels that can lead to condensation build-up on windows, or more serious
moisture problems.
Balanced ventilators, like ERVs and HRVs, also help minimize the risk of chimney back-drafting. Some models have built-in HEPA filters for even better indoor air quality.
You'll have to spend more money in the short-term, but the benefits of this two-pronged approach are multi-fold -- cleaner air, a safer home, lower energy bills, and greater comfort. And believe us, the goopy, sticky stuff that's sticking to the bottom of your humdifier is nasty.
For the intrepid DIY'er, a good selection of home ventilation systems are available at
MoreHome.com, including HRV/ERVs. They compare competitively price-wise, and are
certainly less expensive than what a contractor charges to install (not that it isn't worth, but hey, if you know what you're doing, why not save a few bucks).
Misunderstanding attic ventilation
One of the most misunderstood areas of home construction and maintenance is the long-held rule that attic ventilation helps extend the life of a roof. The general assumption is that ventilation -- whether a ridge-vent, gable vents, or what have you -- allows the attic-space to "air-out," therefore keeping the underside of the roof-decking dry. Sounds reasonable enough. But it's simply unfounded. In the photo (below), this attic was equipped with a ridge-vent, and (visible) soffit vents -- yet still received costly moisture and mold damage. 
Though most building codes require a minimum of 1 sq. ft. of ventilation per every 300 sq. ft., the 300:1 rule, as it is commonly known, has no basis in building science. In fact, a paper titled, "The History of Attic Ventilation, Regulation and Research" found no concrete scientific basis for the 300:1 rule, which was first put in motion in 1942 by writers of the Federal Housing Agency. The rule, according to Rose, was arbitrarily enacted with no research or field-evidence to support it.
Since the 1940's, home construction methods have changed dramatically. Then, roof-decking consisted of board (plank) sheathing, a rather "breathable" material. Today, we employ continuous sheets of plywood or oriented strand board (OSB), which creates a relatively air-tight barrier to the outside. Additionally, homes built in the early to mid-20th century contained little, if any, attic insulation, whereas today, we build tight, well-insulated homes.
This change in building materials and construction techniques creates an entirely different dynamic in terms of the way a home behaves under certain temperature and/or moisture conditions.
When an attic is uninsulated, the space becomes semi-conditioned, as it receives heat that rises and escapes from the conditioned areas below. This rising heat also brings with it moisture, in the form of vapor, the main culprit in roof failures. In a semi-conditioned environment, this moisture tends to stay in vapor state, since the dew-point is never reached, which means condensation can't occur.
In a well-insulated attic, the space becomes completely unconditioned. Little heat reaches the attic, making the attic a much colder space. And since few builders to a good job of air-sealing the attic plane (the ceiling of the rooms below), moisture-vapor still reaches the attic space. Except in this scenario, the temperature of the attic DOES reach dew-point, causing the vapor to condense into liquid water, which ultimately kills the roof.
The point to all of this?
Homeowners in cold climates sometimes experience damaged, decayed roof systems caused by condensing moisture. And when they run into this problem, the first people the often call is a roofer or general contractor. And with almost 100-percent certainty, the first recommendation they make is -- add attic ventilation.
Why is this bad?
Attic ventilation inherently increases the "stack-effect of a home, increasing air and moisture-movement into the attic. More moisture means more problems. Furthermore, there's no scientific evidence that attic ventilation does what it's purported to do, which is allow the roof to air-out and dry sufficiently to head-off moisture-damage. It's merely an assumption that we've all gone along with, without question.
If the roofer or GC is worth their salt, they'll recommend not more attic ventilation, but a combination of air-sealing and MECHANICAL ventilation. Sealing the attic plane keeps moisture out of the attic altogether. Mechanical ventilation, such as a properly sized bathroom, removes excess water-vapor from the entire home.
Cathedral ceilings, where there's no attic at all, receives similar treatment. The ceiling itself should be very well-sealed to prevent moist air from getting inside. If recessed lights are installed in the ceiling, use only sealed canisters. If using a finish other than sheetrock or plywood, such as tongue and groove panels, a continuous moisture-barrier should be installed between the finished ceiling and the rafters.
According to building science expert Joseph Lstiburek, one extra level of defense to protect cathedral ceilings (in cold climates only) is to install a layer of rigid-foam insulation on the outside of the roof-decking. This keeps the underside of the decking warm and inhibits condensation.
The nice thing about the one-two punch of air-sealing and mechanical ventilation, is that it's also better for energy bills, while reducing uncomfortable drafts.
So if you have the great misfortune of a failed roof, don't call the roofer until you've first hired an insulator to seal the home, and an HVAC technician to check and/or upgrade the adequacy of your mechanical ventilation.
Beating high oil prices -- Serious efficiency upgrades you can do for under $1,000
Faced with a near-doubling of oil prices as we head toward another heating season, many homeowners are looking for ways to increase the efficiency of their oil-heating systems. Here are a few recommendations on beating the high cost of oil with upgrades and improvements that cost under $1,000.
1) Outdoor reset control (hot water systems)
Also called weather-responsive controls, these electronic devices operate on the simple premise that lower boiler-supply temperatures results in increased fuel savings.
Most boiler systems are designed to heat the home on the coldest day of the year (in the Albany, NY area, we consider this to be about -7 degrees F) using a boiler supply-temperature of around 180 degrees F.
Since 98 percent of the heating system is above -7 degrees -- 67 percent of the season is actually above 30 degrees F -- it's possible to adequately heat your home with substantially lower boiler-supply temperatures.
Outdoor-reset controls modulate the temperature of the boiler based on the outdoor temperature; increasing water-temperatures as the outdoor temperature drops, and decreasing water-temperatures in milder weather.
Most outdoor-reset controls typically improve boiler-efficiency by 15 percent.
2) Becket HeatManager (hot water systems)
Becket's HeatManager is an add-on boiler control that improves efficiency by better-managing on-off cycling of the oil burner. Costing around $575-$650 installed, the HeatManager comes with 10% fuel-savings guarantee from the manufacturer.
3) Professional clean & tune (hot water, forced air & steam systems)
Most people with oil systems are diligent in having their oil-fired boiler cleaned each season. The problem is that the technician called-in to do the job isn't so diligent in properly tuning the burner for maximum efficiency.
Most technicians fail to use an electronic combustion-analyzer and other diagnostic devices to make precise adjustments to the burner. A thorough cleaning followed by a proper tune-up can improve efficiency by as much as 10 percent.
Contractors and technicians who own the proper testing gear will typically charge $250 to $300 to clean & tune your oil-fired- heating system.
4) Minor ductwork improvements (forced air systems)
The vast majority of duct systems rob the energy-performance of the furnace by as much as 20 percent. Poor duct design and/or installation can cause restrictions in the path of air-flow and force the furnace to work harder than it should.
A simple 5-minute static-pressure test by a knowledgeable technician can reveal energy-robbing air-flow problems, many of which can be remedied with minor changes to the ductwork.
These relatively easy and cost-effective upgrades my include the installation of turning-vanes at critical transitions, or replacing flex-duct with hard pipe.
5) Burner de-rating (Hot Water & Warm Air Systems)
Most homeowners own heating systems that are oversized for their actual needs. The reason for oversizing usually results from the original contractor's failure to perform a proper heat-loss analyses of the home prior to installation. Homeowners faced with this situation can often have their burner "de-rated," or in other words, reduce its output in order to burn less oil.
Burners should only be de-rated by a highly qualified technician. Done incorrectly, one can cause the burner to malfunction and result in frequent lock-outs. More serious, improper de-rating can result in dangerous excessive production of carbon monoxide.
To properly de-rate your burner, a smart technician will first contact the equipment manufacturer, who in turn will provide information on the correct nozzle, as well as the new settings for the burner. Following the manufacturer's guidelines, the technician will fine-tune the burner using an electronic combustion-analyzer and other testing devices.
All of the above upgrades and improvements are available from Enhanced Living, Inc. For consultation, call (518) 235-0311 or e-mail info@enhancedliving.net.
1) Outdoor reset control (hot water systems)
Also called weather-responsive controls, these electronic devices operate on the simple premise that lower boiler-supply temperatures results in increased fuel savings.
Most boiler systems are designed to heat the home on the coldest day of the year (in the Albany, NY area, we consider this to be about -7 degrees F) using a boiler supply-temperature of around 180 degrees F.
Since 98 percent of the heating system is above -7 degrees -- 67 percent of the season is actually above 30 degrees F -- it's possible to adequately heat your home with substantially lower boiler-supply temperatures.
Outdoor-reset controls modulate the temperature of the boiler based on the outdoor temperature; increasing water-temperatures as the outdoor temperature drops, and decreasing water-temperatures in milder weather.
Most outdoor-reset controls typically improve boiler-efficiency by 15 percent.
2) Becket HeatManager (hot water systems)
Becket's HeatManager is an add-on boiler control that improves efficiency by better-managing on-off cycling of the oil burner. Costing around $575-$650 installed, the HeatManager comes with 10% fuel-savings guarantee from the manufacturer.
3) Professional clean & tune (hot water, forced air & steam systems)
Most people with oil systems are diligent in having their oil-fired boiler cleaned each season. The problem is that the technician called-in to do the job isn't so diligent in properly tuning the burner for maximum efficiency.
Most technicians fail to use an electronic combustion-analyzer and other diagnostic devices to make precise adjustments to the burner. A thorough cleaning followed by a proper tune-up can improve efficiency by as much as 10 percent.
Contractors and technicians who own the proper testing gear will typically charge $250 to $300 to clean & tune your oil-fired- heating system.
4) Minor ductwork improvements (forced air systems)
The vast majority of duct systems rob the energy-performance of the furnace by as much as 20 percent. Poor duct design and/or installation can cause restrictions in the path of air-flow and force the furnace to work harder than it should.
A simple 5-minute static-pressure test by a knowledgeable technician can reveal energy-robbing air-flow problems, many of which can be remedied with minor changes to the ductwork.
These relatively easy and cost-effective upgrades my include the installation of turning-vanes at critical transitions, or replacing flex-duct with hard pipe.
5) Burner de-rating (Hot Water & Warm Air Systems)
Most homeowners own heating systems that are oversized for their actual needs. The reason for oversizing usually results from the original contractor's failure to perform a proper heat-loss analyses of the home prior to installation. Homeowners faced with this situation can often have their burner "de-rated," or in other words, reduce its output in order to burn less oil.
Burners should only be de-rated by a highly qualified technician. Done incorrectly, one can cause the burner to malfunction and result in frequent lock-outs. More serious, improper de-rating can result in dangerous excessive production of carbon monoxide.
To properly de-rate your burner, a smart technician will first contact the equipment manufacturer, who in turn will provide information on the correct nozzle, as well as the new settings for the burner. Following the manufacturer's guidelines, the technician will fine-tune the burner using an electronic combustion-analyzer and other testing devices.
All of the above upgrades and improvements are available from Enhanced Living, Inc. For consultation, call (518) 235-0311 or e-mail info@enhancedliving.net.
Water-heaters: On-demand tankless vs. Indirect-fired storage tanks
What's better -- tankless, on-demand water heaters or indirect-fired storage tanks? This question gets asked to us at least once a week. My answer: it depends.
Tankless water-heaters:
Tankless, on-demand water heaters like those by Rinnai, Bosch, Takagi and many others, are a major improvement from the old-fashioned atmospheric domestic hot water tank. With a typical efficiency factor of .55, standard water heaters waste most of their energy while sitting unused, losing their heat through wimpy insulation, and an exhaust-pipe connected to the outside. Tankless, on-demand water heaters avoid these "standy-losses" by avoiding the whole process of storage altogether.
From a combustion-efficiency standpoint, gas-fired on-demand water heaters get a so-so grade. Most models usually come with efficiency-ratings between 81 and 85 percent. Not terrible, but not record-breaking, either.
(NOTE: If you're served by low-cost electricity, an electric on-demand water heater -- virtually 100 percent-efficient with no combustion whatsoever -- might be the way to go.)
Indirect-fired DHW:
Indirect-fired water heaters are insulated storage vessels that are heated indirectly, usually from a hot water boiler. Although they store hot water, they have no flue-pipe from which heat can escape.
The efficiency of indirect-fired water heaters depends chiefly on two factors -- the effectiveness of the tank's insulation, and the efficiency of the boiler it's connected to.
With a few cheap exceptions, most indirect-fired water heaters have two inch-thick polyurethane foam insulation. With two inches of insulation, most indirect-fired tanks have a standby-loss of around a half-degree per hour -- in most cases, a negligible loss.
Modern boiler efficiencies usually range in between 84 and 95 percent. If the indirect-fired storage tank is located near the boiler and the supply/return piping is insulated to minimize energy-losses, the efficiency of the water heater will be close to that of the boiler.
Side-by-Side Comparison:
From an energy-efficiency standpoint, on-demand water heaters and indirect-fired storage tanks are, for all intents and purposes, fairly equal.
From an installation-cost standpoint, in most cases, the two options are close in price, depending on the size and quality of the equipment you select and the difficulty of the installation.
The final factor in deciding the better of the two options is life-expectancy.
Most on-demand water heater manufacturers offer a ten to twelve-year limited warranty. The practical life-expectancy of on-demand units is somewhere around 15 years, depending on water conditions and other factors.
The life expectancy of indirect-fired water heaters, on the other hand, can range widely depending on the material they're made from. Lower-end coated steel tanks can last anywhere from eight to twenty years, while higher-quality stainless-steel cylinders are covered by lifetime warranties.
Final analysis:
I like both indirect-fired tanks and on-demand -- each one has their place. If you have a furnace and not a boiler, and use a fairly standard amount of hot water, an on-demand water heater is the way to go.
If you don't have a boiler, and have exceptionally large water-heating needs (more than a typical 40-gallon water heater can provide), a high-efficiency tank-type water heater such as A.O. Smith's Vertex would probably be better match for your lifestyle.
If you have a fairly modern boiler, a well-made, well-insulated indirect-fired storage tank would be the best choice. In addition to the long life-expectancy, it's always safer and requires less maintenace when you minimize your combustion-appliances -- one source of combustion is better than two.
So, what's better -- a tankless, on-demand water heater or an indirect-fired storage tank? It depends!
Tankless water-heaters:
Tankless, on-demand water heaters like those by Rinnai, Bosch, Takagi and many others, are a major improvement from the old-fashioned atmospheric domestic hot water tank. With a typical efficiency factor of .55, standard water heaters waste most of their energy while sitting unused, losing their heat through wimpy insulation, and an exhaust-pipe connected to the outside. Tankless, on-demand water heaters avoid these "standy-losses" by avoiding the whole process of storage altogether.
From a combustion-efficiency standpoint, gas-fired on-demand water heaters get a so-so grade. Most models usually come with efficiency-ratings between 81 and 85 percent. Not terrible, but not record-breaking, either.
(NOTE: If you're served by low-cost electricity, an electric on-demand water heater -- virtually 100 percent-efficient with no combustion whatsoever -- might be the way to go.)
Indirect-fired DHW:
Indirect-fired water heaters are insulated storage vessels that are heated indirectly, usually from a hot water boiler. Although they store hot water, they have no flue-pipe from which heat can escape.
The efficiency of indirect-fired water heaters depends chiefly on two factors -- the effectiveness of the tank's insulation, and the efficiency of the boiler it's connected to.
With a few cheap exceptions, most indirect-fired water heaters have two inch-thick polyurethane foam insulation. With two inches of insulation, most indirect-fired tanks have a standby-loss of around a half-degree per hour -- in most cases, a negligible loss.
Modern boiler efficiencies usually range in between 84 and 95 percent. If the indirect-fired storage tank is located near the boiler and the supply/return piping is insulated to minimize energy-losses, the efficiency of the water heater will be close to that of the boiler.
Side-by-Side Comparison:
From an energy-efficiency standpoint, on-demand water heaters and indirect-fired storage tanks are, for all intents and purposes, fairly equal.
From an installation-cost standpoint, in most cases, the two options are close in price, depending on the size and quality of the equipment you select and the difficulty of the installation.
The final factor in deciding the better of the two options is life-expectancy.
Most on-demand water heater manufacturers offer a ten to twelve-year limited warranty. The practical life-expectancy of on-demand units is somewhere around 15 years, depending on water conditions and other factors.
The life expectancy of indirect-fired water heaters, on the other hand, can range widely depending on the material they're made from. Lower-end coated steel tanks can last anywhere from eight to twenty years, while higher-quality stainless-steel cylinders are covered by lifetime warranties.
Final analysis:
I like both indirect-fired tanks and on-demand -- each one has their place. If you have a furnace and not a boiler, and use a fairly standard amount of hot water, an on-demand water heater is the way to go.
If you don't have a boiler, and have exceptionally large water-heating needs (more than a typical 40-gallon water heater can provide), a high-efficiency tank-type water heater such as A.O. Smith's Vertex would probably be better match for your lifestyle.
If you have a fairly modern boiler, a well-made, well-insulated indirect-fired storage tank would be the best choice. In addition to the long life-expectancy, it's always safer and requires less maintenace when you minimize your combustion-appliances -- one source of combustion is better than two.
So, what's better -- a tankless, on-demand water heater or an indirect-fired storage tank? It depends!
Radiant Heating 101: Mixing valves and controls for in-floor radiant heating
A solid control apparatus is the cornerstone of a well-designed in-floor radiant heating system. The chief function of a control system is to modulate and limit water-temperatures to maximize efficiency and to insure against over-heated floors.
There’s two dominant methods for controlling and modulating water-temperatures – mixing valves and injection pumps.
Mixing valves come in two varieties: 3-way and 4-way mixing valves.
A 3-way mixing valve has three pipe connections – hot (from the boiler), cold (from the floors) and a mix port (supply to the floors). The mix port blends hot water from the boiler with cooler water returning from the floors. This is how the mixing valve reduces the temperature of the water as it flows through the floors.
A 4-way mixing valve also reduces water temperatures flowing to the floors like a 3-way valve. However, at the same time, it uses one additional port to ensure that hotter water returns back to the boiler. This serves the function of protecting the boiler from “thermal shock,” which can ruin most cast-iron boilers.
A 3-way mixing valve can be used instead of a 4-way valve under the following conditions:
1) When a condensing boiler constructed of stainless steel or aluminum is used. Condensing boilers do not need protection against low water temperatures, and, in fact, increase in efficiency the colder the water is.
2) The system employs large-mass boiler with significant (I mean significant) water-volume. A fine example of a large-mass boiler that does not require protection from low water-temperatures is Viessmann’s Vitola 200.
3) A primary-secondary piping system is employed. The primary loop, also called the “hot loop,” serves the role of protecting the boiler.
4) In a two-temperature system where the proportion of “low-temperature” heating (i.e. radiant floor heat) is small relative to the “high-temperature” (i.e. baseboard convectors, radiators, etc.) zones
Both 3-way and 4-way mixing valves modulate water temperatures by means of an actuator motor that hooks directly to the valve. The actuator opens and closes the valve to raise or lower the water temperatures flowing through the floors. This actuator will get its instructions via some type of electronic control device.
When purchasing a “motorized” mixing valve, bear in mind that actuator motors are designed specifically for a particular mixing valve model. If you get a Honeywell mixing valve, you need the matching Honeywell actuator motor – there’s no mixing and matching among manufacturers.
Furthermore, there are two dominant styles of motorized mixing valves: rotary and diverting.
Diverting-type valves are the simpler and usually less expensive of the two styles, and operates like a gate valve with three positions – open, close and mix. While fully open, the water will be hot. When fully closed, the water will be cold. When in the middle (mix), they’ll do just that. When budget is a concern, or the amount of radiant floor heat is relatively small, I’ll sometimes opt for less-expensive diverting valve, such as those made by Oventrop.
When the radiant load is large and I’m looking for greater accuracy in the water temperatures, a rotary valve will be utilized. A rotary valve utilizes an internal “paddle” that mixes water across a full range of temperatures. Examples include: Viessmann, DISMY (Danfoss), Rehau, Viega and Tekmar.
No matter which type of mixing valve is used – and they all work reasonably well – they’re only as good as their controller. Up until fairly recently, there weren’t too many options for mixing controls. The main player was Tekmar, who still is the major supplier. In addition to producing controls under their own label, they also private-label for other manufacturers including Viega, Taco, Watts and others.
Tekmar controls, such as the 360 Control, work very well in operating a mixing-valve. In addition to modulating the mixing valve, the 360 provides an outdoor boiler-reset function. If multiple mixing valves are to be used and/or you wish the control to perform other functions such as domestic hot water (with an indirect-fired storage tank), more sophisticated Tekmar controls are available. Another advantage of the Tekmar line is that they can be used with most any manufacturer’s mixing valves.
As far as proprietary brands go, I find Viessmann’s HK 1M Universal mixing control useful. The control is integrated within the housing of the actuator motor, and gives the system a very sophisticated look.
What I find attractive is not so much the control (which is very good), but Viessmann’s mixing valves. I find Viessmann’s 3-way and 4-way mixing valves to be among the highest quality, longest-lasting, and dead-nuts accurate. Their strength lies in their elegantly simple design.
For a simple and cheap mixing valve and controller, there’s also the Taco i-Series valves. They are cost-effective solution for smaller radiant applications where super-accurate temperature-modulation isn’t required.
As an alternative to mixing valves, it’s important to mention injection systems as a means of controlling water-temperatures. Instead of using a mixing valve, injection systems use a variable speed circulator pump to “inject” hot water from the boiler into the radiant system.
Injection systems do work well, however they require the use of many additional (unnecessary) pumps – at least three, but usually more -- in order to function.
Injection systems require the designer to employ primary-secondary piping. This means you have a primary pump on the boiler, a secondary pump for the main distribution loop, and typically, additional zone pumps. The actual injection pump itself sits between the primary and secondary loop. Too much for an otherwise simple job, in my opinion. As you would expect, an engineer developed this type of system!
As much as poo-poo injection, there are rare instances where this is the smarter, simpler option. These instances are very rare and usually only occur in larger commercial applications or huge McMansions where the system becomes very sophisticated -- not in basic residential jobs.
If you do choose to go with injection, you’ll need a controller just like you would with a mixing valve. Again, Tekmar is the primary player for these controls.
Finally, it is very common for many contractors, and especially DIY’ers, to substitute a modulating motorized mixing valve with a cheap thermostatic or fixed mixing valve intended for water-heating.
In many applications, it gets the job done, and on a few occasions, have done it myself. While it does serve the function of limiting outgoing supply-water temperatures, it doesn’t modulate, nor does it add any energy-efficiency benefits that a motorized valve brings to the table. Where it works is on a small, isolated radiant loop - when you’re trying to put some heat under a bathroom floor, for example.
I wouldn’t use a cheap fixed mixing valve to do an entire house. Nor would I use one when heating a concrete slab. Concrete slabs hold a tremendous amount of mass. They take a long time to heat up, but more critically, they take just as long to cool off if they become overheated. In my view, modulating mixing valves on an outdoor-reset are a must for slab applications.
There’s two dominant methods for controlling and modulating water-temperatures – mixing valves and injection pumps.
Mixing valves come in two varieties: 3-way and 4-way mixing valves.
A 3-way mixing valve has three pipe connections – hot (from the boiler), cold (from the floors) and a mix port (supply to the floors). The mix port blends hot water from the boiler with cooler water returning from the floors. This is how the mixing valve reduces the temperature of the water as it flows through the floors.
A 4-way mixing valve also reduces water temperatures flowing to the floors like a 3-way valve. However, at the same time, it uses one additional port to ensure that hotter water returns back to the boiler. This serves the function of protecting the boiler from “thermal shock,” which can ruin most cast-iron boilers.
A 3-way mixing valve can be used instead of a 4-way valve under the following conditions:1) When a condensing boiler constructed of stainless steel or aluminum is used. Condensing boilers do not need protection against low water temperatures, and, in fact, increase in efficiency the colder the water is.
2) The system employs large-mass boiler with significant (I mean significant) water-volume. A fine example of a large-mass boiler that does not require protection from low water-temperatures is Viessmann’s Vitola 200.
3) A primary-secondary piping system is employed. The primary loop, also called the “hot loop,” serves the role of protecting the boiler.
4) In a two-temperature system where the proportion of “low-temperature” heating (i.e. radiant floor heat) is small relative to the “high-temperature” (i.e. baseboard convectors, radiators, etc.) zones
Both 3-way and 4-way mixing valves modulate water temperatures by means of an actuator motor that hooks directly to the valve. The actuator opens and closes the valve to raise or lower the water temperatures flowing through the floors. This actuator will get its instructions via some type of electronic control device.
When purchasing a “motorized” mixing valve, bear in mind that actuator motors are designed specifically for a particular mixing valve model. If you get a Honeywell mixing valve, you need the matching Honeywell actuator motor – there’s no mixing and matching among manufacturers.
Furthermore, there are two dominant styles of motorized mixing valves: rotary and diverting.
Diverting-type valves are the simpler and usually less expensive of the two styles, and operates like a gate valve with three positions – open, close and mix. While fully open, the water will be hot. When fully closed, the water will be cold. When in the middle (mix), they’ll do just that. When budget is a concern, or the amount of radiant floor heat is relatively small, I’ll sometimes opt for less-expensive diverting valve, such as those made by Oventrop.
When the radiant load is large and I’m looking for greater accuracy in the water temperatures, a rotary valve will be utilized. A rotary valve utilizes an internal “paddle” that mixes water across a full range of temperatures. Examples include: Viessmann, DISMY (Danfoss), Rehau, Viega and Tekmar.
No matter which type of mixing valve is used – and they all work reasonably well – they’re only as good as their controller. Up until fairly recently, there weren’t too many options for mixing controls. The main player was Tekmar, who still is the major supplier. In addition to producing controls under their own label, they also private-label for other manufacturers including Viega, Taco, Watts and others.
Tekmar controls, such as the 360 Control, work very well in operating a mixing-valve. In addition to modulating the mixing valve, the 360 provides an outdoor boiler-reset function. If multiple mixing valves are to be used and/or you wish the control to perform other functions such as domestic hot water (with an indirect-fired storage tank), more sophisticated Tekmar controls are available. Another advantage of the Tekmar line is that they can be used with most any manufacturer’s mixing valves.
As far as proprietary brands go, I find Viessmann’s HK 1M Universal mixing control useful. The control is integrated within the housing of the actuator motor, and gives the system a very sophisticated look.
What I find attractive is not so much the control (which is very good), but Viessmann’s mixing valves. I find Viessmann’s 3-way and 4-way mixing valves to be among the highest quality, longest-lasting, and dead-nuts accurate. Their strength lies in their elegantly simple design.
For a simple and cheap mixing valve and controller, there’s also the Taco i-Series valves. They are cost-effective solution for smaller radiant applications where super-accurate temperature-modulation isn’t required.
As an alternative to mixing valves, it’s important to mention injection systems as a means of controlling water-temperatures. Instead of using a mixing valve, injection systems use a variable speed circulator pump to “inject” hot water from the boiler into the radiant system.
Injection systems do work well, however they require the use of many additional (unnecessary) pumps – at least three, but usually more -- in order to function.
Injection systems require the designer to employ primary-secondary piping. This means you have a primary pump on the boiler, a secondary pump for the main distribution loop, and typically, additional zone pumps. The actual injection pump itself sits between the primary and secondary loop. Too much for an otherwise simple job, in my opinion. As you would expect, an engineer developed this type of system!
As much as poo-poo injection, there are rare instances where this is the smarter, simpler option. These instances are very rare and usually only occur in larger commercial applications or huge McMansions where the system becomes very sophisticated -- not in basic residential jobs.
If you do choose to go with injection, you’ll need a controller just like you would with a mixing valve. Again, Tekmar is the primary player for these controls.
Finally, it is very common for many contractors, and especially DIY’ers, to substitute a modulating motorized mixing valve with a cheap thermostatic or fixed mixing valve intended for water-heating.
In many applications, it gets the job done, and on a few occasions, have done it myself. While it does serve the function of limiting outgoing supply-water temperatures, it doesn’t modulate, nor does it add any energy-efficiency benefits that a motorized valve brings to the table. Where it works is on a small, isolated radiant loop - when you’re trying to put some heat under a bathroom floor, for example.
I wouldn’t use a cheap fixed mixing valve to do an entire house. Nor would I use one when heating a concrete slab. Concrete slabs hold a tremendous amount of mass. They take a long time to heat up, but more critically, they take just as long to cool off if they become overheated. In my view, modulating mixing valves on an outdoor-reset are a must for slab applications.
Is in-floor radiant heat efficient?
The answer to whether radiant heat is efficient is yes and no. Radiant floor-heating is nothing but a form of radiator.
Instead of using finned-baseboard, cast-iron floor radiators or flat-panel wall radiators, you're using tubing on or below the floor as the source of heat-radiation. And like any of the other radiator options, it can be designed and installed efficiently or it can be made to run like a hog.
Several factors can make or break the efficiency of your radiant heating system.
1) Insulate under the floor
Unlike a forced-air heating system, which causes warm air to rise, radiant heating radiates in any and every direction. Moreover, due to the laws of thermodynamics, the heat emitted from the tubing will want to go towards the coldest path. If that path happens to be down (toward a cold basement, perhaps), that's where the heat will go.
The better you insulate below the floor, the more efficient the system will be at delivering heat into the room in which it was intended. Most manufacturers recommend a minimum of R-13 (about 4" of fiberglass). Don't rely on thin Astro-Foil (the stuff with bubbles) to do the job, as many people make the mistake of doing.
One can reasonably argue that radiant floor-heating is less efficient than radiators installed within the room. If the radiators are over-sized, like many old cast-iron radiators are, this is true, since there are no downward heat losses associated with radiators.
2) Minimize water temperatures
A well-designed radiant floor heating system should never exceed water-temperatures of (approx.) 135 degrees (F). The lower your water temperature, the more efficient the system will be. In many cases, it's possible to operate a system with maximum water-temperatures of 110-115 degrees (F). You can accomplish this by installing tubing at closer spacing (6" OC versus 9" or 12").
3) Utilize a modulating control system
When we talk about a system's design-temperature, we're talking about the water-temperature needed to heat the home on the coldest day of the year. The rest of the time we can run the system at a lower supply-water temperature.
This can be accomplished automatically with a modulating control system that utilizes a boiler-reset control (w/ either an indoor and/or outdoor temperature sensor), and a modulating mixing-valve or variable-speed injection pump. I prefer mixing-valves over injection pumps, as mixing valves require just one pump versus three (primary loop pump + injection pump + secondary loop pump) for an injection system. That said, both methods modulate water temperatures based on outdoor and/or indoor temperatures. Lower water temperatures mean higher efficiency.
4) Use the right boiler
When shooting for efficiency, the standard boiler has become wall-hung condensing models. Condensing boilers often reach efficiencies of up to 95-96 percent. Sophisticated models often have built-in outdoor-reset controls and fully modulating burners to minimize water-temperatures and maximize combustion-efficiency. Condensing boilers run the gamut in terms of price and quality. Like anything else, you really get what you pay for -- and it pays to pay more. Look for models with stainless-steel heat-exchangers (avoid aluminum or copper) and fully modulating burners (versus one or two stage).
Instead of using finned-baseboard, cast-iron floor radiators or flat-panel wall radiators, you're using tubing on or below the floor as the source of heat-radiation. And like any of the other radiator options, it can be designed and installed efficiently or it can be made to run like a hog.
Several factors can make or break the efficiency of your radiant heating system.
1) Insulate under the floor
Unlike a forced-air heating system, which causes warm air to rise, radiant heating radiates in any and every direction. Moreover, due to the laws of thermodynamics, the heat emitted from the tubing will want to go towards the coldest path. If that path happens to be down (toward a cold basement, perhaps), that's where the heat will go.
The better you insulate below the floor, the more efficient the system will be at delivering heat into the room in which it was intended. Most manufacturers recommend a minimum of R-13 (about 4" of fiberglass). Don't rely on thin Astro-Foil (the stuff with bubbles) to do the job, as many people make the mistake of doing.
One can reasonably argue that radiant floor-heating is less efficient than radiators installed within the room. If the radiators are over-sized, like many old cast-iron radiators are, this is true, since there are no downward heat losses associated with radiators.
2) Minimize water temperatures
A well-designed radiant floor heating system should never exceed water-temperatures of (approx.) 135 degrees (F). The lower your water temperature, the more efficient the system will be. In many cases, it's possible to operate a system with maximum water-temperatures of 110-115 degrees (F). You can accomplish this by installing tubing at closer spacing (6" OC versus 9" or 12").
3) Utilize a modulating control system
When we talk about a system's design-temperature, we're talking about the water-temperature needed to heat the home on the coldest day of the year. The rest of the time we can run the system at a lower supply-water temperature.
This can be accomplished automatically with a modulating control system that utilizes a boiler-reset control (w/ either an indoor and/or outdoor temperature sensor), and a modulating mixing-valve or variable-speed injection pump. I prefer mixing-valves over injection pumps, as mixing valves require just one pump versus three (primary loop pump + injection pump + secondary loop pump) for an injection system. That said, both methods modulate water temperatures based on outdoor and/or indoor temperatures. Lower water temperatures mean higher efficiency.
4) Use the right boiler
When shooting for efficiency, the standard boiler has become wall-hung condensing models. Condensing boilers often reach efficiencies of up to 95-96 percent. Sophisticated models often have built-in outdoor-reset controls and fully modulating burners to minimize water-temperatures and maximize combustion-efficiency. Condensing boilers run the gamut in terms of price and quality. Like anything else, you really get what you pay for -- and it pays to pay more. Look for models with stainless-steel heat-exchangers (avoid aluminum or copper) and fully modulating burners (versus one or two stage).
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