Image Credit: Charles Hoxie
More Musings of an Energy Nerd
Most builders and designers involved with green building have heard of Henry Gifford. Energy efficiency experts admire his deep knowledge of heating systems and his straight talk about the unacceptably high number of HVAC problems in run-of-the-mill new buildings in the U.S. At the headquarters of the United States Green Building Council (USGBC), on the other hand, he is something of a pariah — due in part to his 2010 lawsuit that accused the USGBC of making “deceptive marketing claims.”
Gifford lost his suit. Yet even those who doubt the usefulness of Gifford’s litigious tactics usually admit that he has a point: many LEED-certified buildings use so much energy that they don’t even meet Energy Star standards. Due in part to Gifford’s needling, the USGBC has implemented changes in the LEED program that attempt to address some of Gifford’s concerns.
Gifford knows more about boilers and heating system design than almost any mechanical engineer in the country. I recently reached him by telephone for a one-hour interview.
Q. What recommendations do you have for the design of heating or ventilating systems for single-family homes?
Henry Gifford: A nice successful person, who society rewards with a three-bedroom house in the suburbs, usually gets a master suite with its own bathroom. Usually, the house has a duct system that blows 400 cfm of heating and cooling air into the bedroom all day. The air comes out the bedroom door, down the hallway past the thermostat, back into the central return near the kitchen, through the air handler and back around again.
At night, guess what happens? Somebody closes the bedroom door. Now the air pressure in the bedroom goes up, so now only 300 cfm gets delivered to the bedroom. Maybe 100 cfm goes through the bathroom exhaust duct through…
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37 Comments
Passive House Heating
Henry Gifford:"The standard is great because it gets us just to but not beyond the critical point where we can avoid the cost of the separate heating system." "No one I know of — including me — has had the courage to design a building that way yet, but it’s not the fault of the Passivhaus standard."
The Naugler House has achieved just this!! the only source of heating for the house is a small heater in the HRV fresh air feed. it has kept the house at temperature all winter! This in New Brunswick, Canada 8551.26 F HDD it's very possible! and cost effectively as well. For more information visit http://www.NauglerHouse.com
Really enjoyed the article!!
TX & AZ are not NYC
I don’t think I’ll buy the argument of cooling homes with dehumidifiers only in the South and Southwest, and maybe some data would be helpful. You can lower temperatures 6-8°F by removing humidity, but that’s far from 2-3 summer months of +100°F day and +90°F night temperatures.
I would like to hear more
I would like to hear more about mr Gifford measurements on mini split heating COP .
Tim,my canadian friend, last time i visited your website i was wondering exactly what you just confirmed ... "are they using only the 2KW inline heater for the hole house??? "
Well all i can say is CONGRATS :)
and i also love your HRV air preheating ( could also be used to precool in summer??!! )
and if you grant me permission, i will be using this technique in my next designs
( and will probably recycle my ground water loops to do the same in my own house ! )
About mr Gifford comment on passivhaus standard...
I personally believe in "singular perfection" as there may be only 1 perfect design for a given situation and we can only strive to close it by choosing a certain path of compromises
so the current PH stadard is great step forward, but is not good for every climate and situation.
If you plan the energy used by a building over 100-200 years , then currently it is a supber standard,
but in the near future, new technologies might render what we are using now for windows and insulation ..obsolete and or ineffective ..thus planning for 100yeasr with current high costs materials is not really smart.
The Naugler house
I was intrigued by Tim Naugler's comment, and so I called him up for more information.
Here's what he told me:
The fresh air output from the HRV is equipped with a 2,000-watt electric-resistance heating element.
The house measures 1,900 sq. ft. and has two occupants.
While the ASHRAE 62.2 ventilation rate for this house is 34 cfm, it is being ventilated at twice the ASHRAE rate (70 cfm).
The electric-resistance element modulates to limit the temperature of the ventilation air to no more than 95°F.
The design heat load of the house is only 1.2 kW (4,106 Btu/h).
nice numbers, but why 70cfm
nice numbers, but why 70cfm Tim ??
Usually, unless u are using high indoor polluants , one can get out with lower numbers than 62.2 nah?
Tim i would be interested to know what was ur actual heating costs if you have gone through a full cycle with equipment isntalled already. ( sorry for HJ the thread a bit )
Response to Jin Kazama
Jin,
I had the same question. It's generally hard to heat a cold-climate house by raising the temperature of the ventilation air if you stick with the ASHRAE 62.2 ventilation rate.
I wrote about this problem in a blog I published in April 2011: "A designer striving to deliver all space heat through ventilation ducts actually has a perverse incentive to overventilate the house, since an increase in the ventilation air flow rate may be the only way to deliver enough heat to keep the occupants comfortable. Clearly, overventilation is undesirable, because it incurs an energy penalty."
The Naugler House
Just a quick note. I double checked a few things to make sure i did not feed Martin false information. The 2KW heater is capable of putting out higher temperatures. But the max measured output from the ducts that we have seen is 95F and that was with turning the CMF rate on the HRV up when we were testing the unit. Normal heat output when the heater is turned on is 86F (30C)
The occupants use a lower CFM setting some of the time but they generally keep it on the middle setting approx 70cfm, they find it gives them the air quality that they want.
70 CFM
Jin we are posting daily heating consumption data on the website http://www.nauglerhouse.com/daily-data.html we just started this the last month. The PHPP model put's us at about $100 a year and we believe we are on target.
You can find the Interior and Exterior Min Max temperature, weather conditions, as well as a daily KWH reading on the heater. we averaged around $0.54 a day for January.
These are the CFM settings that we started the project with. after spending some time in the house the Occupants find the lower setting too low and found the house felt a bit stuffy in the morning. They found no temperature discomfort or heating trouble with the lower or higher setting, We do plan to bump the lower setting up a little in order to tune the system to their wishes.
HRV Pre Heat
Yes Jin please feel free to use the pre heat design, it is a very simple version (and we need to publish some more information on it) . I know you can buy such unit's but we decided to try to make our own for a little less. We are finding it amazingly effective and will be specifying it for all future builds. Even when it's -25C the air going into the HRV is above 0C , and yes it does provide some great de humidification of the summer air when it get's humid. we found it was dropping the the incoming air temp about 8C in the summer a huge help!
Tim : i a sorry for
Tim : i a sorry for previously assuming that you were the owner of the house you pointed out..ahah
I just saw the heating data on your website right before reading your entry ..looks good!!
What are you using to recirculate the geo loop for the HRV intake ?
If u are using liquid and pump, how much power is the pump using?
HRV recirc pump
Grundfos alpha is the name of the pump. is pumping 4Gpm and using 43 watts. pretty low consumption. we have it on a temperature switch so it will come on and off as necessary.
Don't worry about the Name
it's called The Naugler House because it's a home that i have built for my parents, and a demonstration / test home for our company.
is this system going to be
is this system going to be used to cool down the summer temp also ?
43w is low..will have to check how much my grundfos pumps use on my system
Response to Jin
Jin,
Don't forget to read the comments before you ask more questions. Tim already answered your latest question. Tim wrote, "Yes, it does provide some great dehumidification of the summer air when it gets humid. We found it was dropping the the incoming air temp about 8°C in the summer."
Oh ouch. I had read it, but
Oh ouch. I had read it, but got distracted by clients and forgot about it. My bad.
Tim: if it works in cold and hot, what did you use for its control?? U mentioned temperature switch??
Maybe a switch with high and low starting points ??
HRV Pre-Heat Location
Tim,
I'm curious: why did you put that geo-loop "pre-heater/warmer" before the HRV and not after?
Doesn't that just reduce the delta-T and therefore also reduce heat transfer from the stale air to the fresh air?
Wouldn't it be better to place it after the HRV on the fresh supply, but before the Thermolec?
Perhaps the geoloop temperatures are too low to make this beneficial except for winter months?
Cheers,
Gio
What would Henry think?
Great article. Thanks Martin. I was wondering what Henry and others would think if LEED adopted the Passive House Standard for its energy efficiency points requirements? This would be a potential benefit to both certification systems: LEED gets the fix on its weakest link and Passive House gains the USGBC marketing machine and the materials toxicity issues that it currently lacks here in the US. The Passive House Institute (http://passivehouse.com) and the global PH community have already discussed this and agreed that it would be a great idea.
Gio Robson: my guess is that
Gio Robson: my guess is that the efficiency of the geo/rad setup is much lower than the HRV
Thus if the HRV has already done its job on the incoming air, the geo will not do much.
what do you think ?
HRV= 50%+ ?
i don't see any regular rad setup going higher than 20-25%
but what do i know enh !! :p
Response to Bronwyn Barry
Bronwyn,
Q. "I was wondering what Henry and others would think if LEED adopted the Passive House Standard for its energy efficiency points requirements?"
A. I'd be interested in Henry's take on this suggestion.
Here's my take: the best way to prove that a building has low energy bills is to report the actual utility bills paid by the owner after a year of operation.
The Passivhaus standard has too many quirks to be a useful design method across all of the climates of North America. In addition to its main quirk -- requiring the same energy use goal per square meter in Minnesota as in San Francisco -- the standard has a second quirk: it does not allow designers to get any credit for an on-site photovoltaic array (even though it allows the designer to get credit for an on-site solar thermal system).
Responses to questions
Henry Gifford here.
To Armando’s question of no air conditioning in Texas, I lived in Texas for a year, and don’t think it should be included in my 2,000 mile wide strip of North America, which of course extends into Canada. But my vagueness is intended to inspire people as to what is possible now or in the future. Living with a cooling dehumidifier in Texas might be possible with aggressive shading on the windows. Add in some really good glass, and the Texas sun isn’t so overwhelming any more.
To Jim’s question of COP measurements, a developer I know wants to change the Federal law that says low income apartment buildings are required to charge really low rents if they have “electric” heat, a category that includes both electric resistance heat and heat pumps. In other words, no incentive to use a heat pump and connect the thermostat to the tenant’s bill. We installed both electric resistance heating and a heat pump in a room over his garage, and a timer that switches between the two every 24 hours. Much monitoring later, and we can compare the electricity use between the systems at any outdoor temperature, and simply divide one by the other to know the COP of the heat pump at any outdoor temp. I won’t reveal our data, but the numbers are really disappointing. And back when amazing claims about ground source heat pumps came out, I bought a $6,000 ultrasonic clamp-on device to measure water flow in a pipe, and also measured electricity use and water temperatures, and measured COP for some systems – COP numbers were truly horrible. Nothing publishing quality on the waterside, but we are thinking about publishing our airsource numbers.
The use of parents as experimental subjects is a great idea, which I will keep in mind, as I don’t have any graduate students around. Naugler’s ventilation air temperature is well below the PassivHaus limit of 50C, set at that limit to prevent pyrolysis of dust in the air, which makes sense to me. In other words, they could turn it up significantly and still be a PassivHaus.
Nobody wrote in to complain about using electric resistance heat, but if anyone does, I think of Marc Rosenbaum’s question about why spend $15,000 on a heating system that will only deliver $100 worth of heat per year. My answer is “so it doesn’t deliver $1,200 worth of heat per year.” Electric resistance heat, despite its high primary energy ratio, solves both problems: it is a $500 heating system that can be relied on to only deliver $100 worth of heat per year.
To Gio’s question of where in the ventilation airstream to best locate the geo coil, the answer to this question can depend on climate, and is especially complicated in a mixed climate, and is one of the places where modeling can be useful. But an easy way to look at it is like the easy way to answer a question in math class about the odds of something happening – calculating the odds of that something not happening. Likewise, for your very cold climate, think of the sequence of equipment which results in the lowest wintertime exhaust ventilation air temperature, which means the system is grabbing the most “free” heat possible. In this case, ignoring the electric heater for a moment, the combination that results in the lowest wintertime exhaust ventilation air temperature is with the geo coil downstream of the ERV. Then the electric coil should, of course, go downstream of everything else, so it “sees” the highest incoming air temperature.
Geo Coil / Rad location and design.
We placed the Geo Coil/rad in the fresh air stream before the HRV. The Geo loop run's at around 5- 8 C depending on the season. It's design was to just preheat the incoming air to above 0C in the wintertime so the built in electric pre-heater within the Zehnder ComfoAir 200 does not kick in. The reason for all of this is to prevent the need for a defrost cycle. so there is no down time where the house is not receiving fresh air. which is important in a super tight house. (in my opinion)
We had a higher power consumption during our December billing than we expected, We believe a large portion of it was that we did not have our temperatures for the Geo control's set quite right so the unit was not circulating when it should have been and the electric pre-heater was kicking on inside the HRV. it's proving a very cost effective addition to our system.
Henery / Martin. What are you feelings on this, do you do anything to prevent typical north american HRV/ERV's from going into a defrost or re-circulation mode? in our climate unit's can be in this defrost or recirc mode up to 1/3 of the time when it's cold. do you see this as a problem to be addressed in tight buildings?
Parent's are great test subjects! especially when they are passionate about energy efficiency! we have learned alot and honed in on lot's of things we will do different/better/easier for next time. Some might call our house a little extreme, but we wanted to push the boundaries and see what was actually possible. and learn from the whole experience. and what worked for our climate! it's been a amazing experience!
The Case Against Gas Heat in Low Energy Homes
Henry says:
" I like a sealed-combustion boiler that makes hot water for space heat and (using an indirect tank) domestic hot water."
and
"Electric resistance heat, despite its high primary energy ratio, solves both problems: it is a $500 heating system that can be relied on to only deliver $100 worth of heat per year."
If we are talking about a new energy efficient house that only needs $100 worth of heat per year, then electric heat is the obvious choice.
Assuming gas at $0.50/therm, there is no gas-fired multi-zone boiler system available that will pay for itself (vs. electric resistance at $0.12/kwh) in that house. In addition to the first cost of the boiler and installation ($3000-$20,000), the gas service fee ($150/yr in Xcel territory) and tap costs ($3000-15,000) far outstrip the energy cost savings.
Even with lousy actual COPs, heat pumps can make the case for electric heat even stronger.
More questions
If I am to understand the article correctly, Henry advocates the use of sealed-combustion equipment with indirect hot water. Forgive me if I am providing a superfluous clarification; I believe he is talking about natural gas equipment and this should be applied to those residences with sufficient heat load (i.e., NOT low energy use homes). Now, how about us poor folks who live in the mountains of Maine where natural gas isn't available and perhaps the home isn't so low energy use (more like 32,000 BTU/HR, design load). Does he still advocate the use of sealed combustion equipment?
In, perhaps, another point of clarification, "moving" heat with water or refrigerant; does he also advocate the use of chilled water as a heat transfer fluid? I would think that fan coils using chilled water (with all of the caveats regarding duct loss, "issues" that he previously discounted) provide a much more versatile means of moving heat; esp in regards to variable cooling/latent heat loads.
Now the problem is that there aren't too many residential options providing chilled water sources.. sigh...
32kbtu/hr & sealed combustion. (response to Bob Manninen)
Sealed combustion propane boilers appropriate to a 32K load are available and allows you to air-seal the house as much as you like without inserting backdrafting risk. Propane/oil combi HW/space-heating water heaters can work too. Sealed combustion removes the influence of any pressure differences between indoors/outdoors on the burner, and keeps the combustion products out of the indoor air.
Micro-zoning with a thermostat in each room adds a LOT of hardware & expense to a heating system, and in the hydronic boiler case, requires higher thermal mass radiation (or a buffering thermal mass like a buffer tank or high mass hydraulic separator) to keep the boiler from short cycling itself into an early demise & low efficiency. In new construction spending the money on a higher performance building, to where point-source heating & cooling works can be a better overall value than on a gazillion -zoned hydronic fossil-burner. Hydronic heat delivery yes, but room by room zoning, probably not- there are rapidly diminishing returns on system efficiency with that route unless MOST of the house is kept at much lower temperature MOST of the time.
At current oil & propane prices ductless air source heat pumps make a lot of sense for po' folks in the mountains of ME with heat loads in the 30KBTU/hr range, but the layout of the house makes a difference of how many ductless heads you'd need. But you can get a LOT out of a 1.5 to 2.5 ton 2-3 head multi-split, and the average per-BTU cost of the heat delivered is less than half that of oil in an 87% burner. During extreme cold weather the cost of operation eventually crosses over, but that crossover point is below 0F for most ME locations. (It really depends on your local utility rates.) Without a head in every room it's point-source heating- you'd have to keep the doors to doored-off rooms open to keep temperature differences from running away, but it's generally more comfortable than heating with a single large wood stove roasting the people in the living room while the remote bedrooms drop to 45F. Figuring out were to place a limited number of ductless heads to get the best function out of them is part engineering, part art, and only YOU know how you intend to use those rooms. A ductless head per room==unaffordable in this lifetime, but 2-3 ductless heads per house displacing oil use usually pays back in under a decade. Many ductless systems have output ratings at -4F/020C, and some even have a spec even at -13F-25C. The efficiency is low at those temps (COP30F the COP is usually 3+, and it's knocking the socks off an oil burner on operating cost. (And they air-condition too.)
Dana
Dana: Re "Hydronic heat delivery yes, but room by room zoning, probably not- there are rapidly diminishing returns on system efficiency with that route unless MOST of the house is kept at much lower temperature MOST of the time." So if a house in zone 8, w/ R50 walls, R85 lid, 10" of EPS under the slab, tight (hopefully) has about 4 zones that are "set and forget" at about 68 F, all should be OK, right? I can not see having thermos in every room, or even many rooms, as I can't imagine being able to keep one room much cooler than the adjacent one. Hydronic floor heat, propane mod/con boiler with HRV that drains into a bucket.
Air Quality in Tight Buildings
My company, Thoughtful Dwellings, worked with Tim Naugler on the design and energy modelling end of the Naugler House project.
Regarding air quality and HRV flow rates:
The 70 cfm air flow for the HRV is what is recommended by the Passive House (PHPP) software. The PHPP recommends a minimum 0.3 ACH (based on usable floor area or TFA) to provide healthy air that doesn't overly dry the house. This 0.3 ACH is also used in our Canadian energy modelling software, HOT2000, as a minimum ventilation standard.
I would much rather ere on the side of healthy indoor air quality than maximizing energy conservation. With an HRV efficiency of 92% this doesn't amount to much anyway. Issues of air and house dryness can be mediated through humidification, if necessary. In my experience a house without a forced air heating system can be much dryer and still feel comfortable. Much of the dryness that people complain of is from dry dust within the air being recirculated within the house. In the Naugler House the only air being circulated comes directly from outside. The Naugler House residents have so far not commented on the air in the house being too dry.
Regarding Heating Load:
The PHPP gives a maximum heating load of 1204 watts (4109 Btu) for the Naugler House. The maximum deliverable heat, based on 120 m3/h (70 cfm) average air flow @ 52C (126F), is 1430 watts (4881 Btu). When we had the system apart we set the thermostat at maximum and measured air flow temperatures above 50C near the heater. With conduction losses through the metal ducts we will likely never see anything near this temperature coming out vents. The PHPP says we actually have enough heat to keep the house at 22.2C (72F) under worst case conditions in our weather region. The homeowners keep the thermostat set at 20C (68F) - sometimes lower at night.
Naugler Monitoring
Hi Tim,
Congrats on the the project.
I'm really interested in the fact that you're doing heating through the ventilation air. My impression was that this was very difficult to do in colder climates and that it makes more sense to do point-source heating. Can you explain your monitoring system that you have publishing to your website? It seems to me that the temperature swings are fairly significant in the house (18 C to 27 C some days) and this would suggest some possible comfort issues for the occupants. Maybe this is just the location of sensors...
Wintertime Peak Load
Hi Martin and Henry,
I enjoyed the interview. Martin, thanks for bringing it to us.
Henry makes a fair point, it's an even greater concern for jurisdictions that are incorporating greater amounts of solar and wind into the grid, with the ultimate aim of eliminating the use of fossil fuels. This big PDF of "Electricity production from solar and wind in Germany in 2012" has some great charts that illustrate the point.
That said since we have to go to zero carbon emissions sooner than most people realize then ultimately heating will have to be met by an electric heating system. So any building heated with gas will have to retrofit their heating system to electric, at some point in the near future.
Kevin Anderson (wikipedia,bio) a professor at the Tyndall Centre for Climate Change makes it pretty clear that if we wait until 2020 to start to reduce CO2 emissions, we will have to eliminate CO2 emissions from energy by 2040 to stay under the 2 degree Celsius threshold agreed to at Copenhagen. Here's his presentation... Real clothes for the Emperor: Facing the challenges of climate change that explains the details.
So to meet our commitments, we have to use heating systems dependent on electricity, because that's how energy from renewables will be delivered. But we also have to manage the wintertime peak load issue. (I live in Quebec where the wintertime peak load dwarfs summertime peak load) So we have to reduce heating demand drastically.... which means build to the Passive House standard.
Any thoughts as to how we design and construct buildings so that we meet our climate change commitments with respect to emissions reductions?
Cheers,
Andrew
On-demand electric water heaters
Given Mr. Gifford's choice of water/liquid as a distribution system and his preference for seal combustion appliances, I wonder why no one is discussing on-demand electric water heaters for home heating especially in applications with very low heat loads. On-demand water heaters are available in very small sizes, at reasonable prices. Maybe Mr. Gifford or others (like those involved with the Naugler house) would comment on why this would be a good or poor choice.
Andrew makes the case that we should be considering electric for any new construction. If a house is well built and tight, with a small heating load I don't see why this wouldn't be the obvious choice especially in new construction.
Thanks for the great discussion.
Peter
IAQ in tight homes and 62.2 infiltration assumption
Very airtight homes that follow the current method of minimum airflow calculation in 62.2 will likely be unventilated. A natural infiltration value is assumed in the standard that is approximately 0.17 ACH, or 0.01 cfm/ft2 (might be a bit higher, can't quite recall off the top of my head). This would leave an ultra-airtight home, like a Passive House, dramatically undervented. If pollutant sources in the home were exceptionally low, this would be fine, but I doubt that is the case. Luckily, the PH standard requires more mechanical venting, and it does so for precisely this reason. Luckily, there is a new calculation method in the latest 62.2 addendum that basically removes the infiltration credit and requires an appropriate airflow for ultra tight homes. I suggest users of this forum use this new equation, which I think is in Addendum N. Cheers.
Re: On-demand electric water heaters
The power authority in New Brunswick, it seems, has a different view toward on-demand hot water heaters...
In the fall we had representatives from NB Power, our power producer in New Brunswick, visit the Naugler House. As they took the tour of the house they seemed quietly impressed by what they saw. As we went through the mechanical systems nothing changed until they saw the on demand hot water heater. They both seemed quite horrified that we would put an on-demand water heater in an energy efficient project like ours.
The power authority is more concerned about peak loads than absolute efficiency or energy use. On-demand water heaters, if many are used simultaneously, are a nightmare from their perspective. Generation for peaks means costly generation that idles most of the time but is always ready for the unknown spike in demand.
As we modernize our grid in New Brunswick we may get peak billing at the residential level. If this happens a well insulated tank with the ability to heat at non-peak times becomes a much more efficient and less costly option. This also considers the primary energy picture - as is promoted by the Passive House approach.
In the Naugler House we have a solar domestic hot water system so the on-demand is just for top-up needs. This being said, and considering the information from the power authority, we will likely consider a small well insulated conventional tank on future projects.
HRVs need drains?
Martin asked: Q. "Why choose an ERV instead of an HRV?"
Henry Gifford answered: "HRVs need drains, and drains are problematic. When you install an HRV, you have to include the cost of the drain. The drain needs to be indirect, with a gap. If there’s a P-trap, the trap can dry out. You can get mold in the drain pans, because of the water. You end up with a biology experiment in the drain pan. I’ve never used an HRV — it makes no sense to me."
All of the reasons Henry cites to avoid HRVs are exactly why we never specified ERVs. Did the world flip? In the Life Breath Clean Air Furnaces we used we had the choice of built in HRV or ERV. We chose the HRV because they didn't require a drain. Was Henry quoted correctly?
On-demand electric water heaters
Hi Garth-
Thanks for your comments about how the power company views on-demand heaters. It's not something I'd considered.
Response to Kim Shanahan
Kim,
You live in New Mexico. I'm not surprised that HRVs don't need drains in New Mexico.
In cold, humid climates, HRVs need drains -- at least most Venmar models do, because I verified the information by calling Venmar. In a dry climate like New Mexico, perhaps drains aren't necessary.
Concerning ERVs, let's poll GBA readers. I know there are many brands of ERVs out there, so I'm asking: how many of them, if any, require drains? Please post your answers on this page.
Renewaire EV130
No Drain.
PanasonicFV-04VE1 WhisperComfort™ Spot ERV
This ERV costs about $400, has no drain, and can satisfy ASHRAE 62.2 for an entire house.
http://www.panasonic.com/business/building-products/ventilation-systems/gbs/ashrae-standards.asp
Response to Peter Burkett
Q. " I wonder why no one is discussing on-demand electric water heaters for home heating especially in applications with very low heat loads".
A. Because it is easier, cheaper, and equally efficient to put electric resistance heaters wherever you need them. A good bathroom unit, for example, costs the same as a kickspace fan coil, but wiring is cheaper than plumbing AND wiring.
Although hot water loops make the best radiant floor systems, Henry considers them overkill (see above).
Radiant floor heating and solar
I agree with just about all the answers in the article with the possible exception of the recommendation against radiant floor heating in one specific case. If you're using gas/oil/electricity to heat and there is no possibility that a solar thermal system will be added in the future, he's right, just use radiators which work fine (even better than high-mass floor heating) and cost a lot less. But solar thermal systems need to run at very low temperatures (down to 80 degrees F or less) for best efficiency and so won't put out enough heat using only radiators. So a low-mass (i.e., staple up or warmboard) radiant floor system is the right solution in that situation.
IMHO a high mass (concrete/gypcrete) radiant floor design is only appropriate in the coldest climates and where passive solar makes up a substantial portion of input (which in turn also requires thick movable insulation and very disciplined and reliable occupants, requirements that are almost never met). For any other case, wall-mounted active collectors and low-mass radiant floor heating is a much better solution than putting lots of big holes (i.e. windows) in the building envelope and then just praying that heat input exceeds output.
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