Dear Umbra,
We're trying to build a really small house and be really economical as we do it. Radiant floor heating sounds practical for the first floor, although it's expensive. What do you think about radiant floor heating, pluses, minuses, efficiency?
Radiantly yours,
Kerry
Florence, Mass.
Dearest Kerry,
Thank you for helping me to write about radiant floor heat basics by sending in your question as requested. How I have coveted a nice radiant floor.
And these little piggies were all warm and toasty.
Photo: iStockphoto
Radiant heat, also known as infrared radiation, heats your floor (and thus you) directly, instead of blowing air around. This is usually achieved through tubing laid below the floor. A classic installation would be a new floor, with insulation laid down, then hydronic tubing arrayed atop the insulation, and concrete poured over to form the body of the floor. Sometimes tiles are a final touch. A boiler or solar-heating system attached to the tubes circulates warm water through them, which warms the floor, which warms you as you happily scoot about in your bare feet. Electric radiant tubing exists but is less common. The tubes can also be installed under a wooden subfloor, between the joists, if you have access there. "Wet" installation in concrete is said to be the most efficient use of the technology, however.
Radiant floor heat has a number of comfort advantages over other common systems. You feel warmer with the thermostat at the same temperature, you get to walk around barefoot in the winter, there's no forced air recirculating so there tends to be less dust, it's silent, and there are no heat registers or radiators on the walls blocking your ideal furniture arrangement. It's lovely, really. Great for someone who likes to lie about on the floor -- and of course all the advertisements depict dogs and crawling babies partying down.
These systems have some energy-efficiency advantages, as well. They're usually more efficient than forced air, partially because hot air is lost through forced-air ducts before it reaches its target, and are more efficient than baseboard heat. Also apparently radiant floors allow less infiltration by cold air from the outside, known as a "stack effect" -- I don't fully understand this, to be honest, but from what I can tell, hot air normally creates a pressure differential as it rises and exits the house, and cold air in turn enters the house. This happens less with radiant heat because there's no phase where the house air gets hotter than the thermostat temperature. There also are claims that persons keep their thermostats set lower with radiant floors because they feel warmer at lower temperatures, but this is largely unproven.
Which leads us to the juicy article from Building Green that makes a persuasive argument that radiant floor heat is not necessarily the best choice for new green construction.
Remember, we've discovered over the years that the important first steps in green home design, including and especially remodeling, are to button down the house. Insulating, reducing leaks, reglazing or replacing windows, all come before the sexy radiant heating system. After the house shell has been made more energy efficient, then we can gauge the correct size of our heating and cooling systems. This juicy Building Green article makes the case that in well-built homes, radiant heat is not worth the costs, because the heating load of the home will be quite low. The article is quite thorough with its evaluation, so give it a read as you consult with your local expert. Apparently radiant systems can be very expensive, in the realm of $10,000. All else being equal, that right there is the main downside.
Still, they are dang cozy.
Dreamily,
Umbra
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Comments
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rivergal Posted 4:36 am
18 Jul 2007
The authors work in Loveland Colorado, which at 40 N latitude is a lot closer to the equator than where I live (61 N). As they say, their review of radiant heat is relevant to houses in "moderate-to-cold" climates. In places like AK where there is virtually no solar gain during the coldest winter months (our sun is only a few degrees above the horizon for 3-5 hours/day), passive solar is not an option for replacing or supplementing active heating systems.
They say that much heat is lost to the ground with slab-on-grade radiant-floor heating systems. I'm sure that's true. But you generally don't see slab-on-grade in areas where frost penetrates deep into the ground, because such foundations would soon crack with frost heaving. I've never seen a slab-on-grade house here in AK or in New England. We have to have full, deep, well-insulated basements or crawl spaces to keep our houses on the level.
They note that most radiant-floor heating systems cannot provide cooling. Not an issue here where the average maximum temperature during our warmest week of the year is 66 F. We have air conditioning -- it's called an open door or window!
I currently live in a house with hot water baseboard heat, which isn't as bad as forced air, but nowhere near as nice as the radiant heat systems some of my friends have. Something the "Green Building" authors do not talk about is thermal mass: any liquid-based heating system has more mass than does hot air. Yes, this means there can be a lag between turning up the thermostat and starting to feel warm. But it also means the house maintains a comfortable temperature more easily, with fewer drafts and cold spots. You can set the thermostat and leave it (or better still, use a programmable one) instead of having to toggle it up and down as the blower kicks on and off on a really cold day.
Having experienced all three kinds of conventional heating systems, plus passive solar, wood, and wood pellet, in AK, northern New England, and the Maritime provinces, I still choose radiant floor heat (maybe with wood backup/area heat) in a location where solar can't do the job.
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Vikingsson Posted 4:56 am
18 Jul 2007
But in our instant gratification society it can be a hard sell since getting a frozen house up to temp takes longer. But boy does it feel better. No more dry stuffy pressure zones, noise, and dust. As a retrofit you can leave the central air system in place and use it for supplementary heating/cooling.
But cost always wins out even if long term it is much cheaper. Same for geothermal, fuel is free but install cost is high. What I see as possible is district heating systems so that hot water is piped to the house which is then used in your radiant system and general hot water needs. Why I still never see innovation like this during large suburban builds is beyond me. Endless ticky tacky houses and not a solar panel or geothermal bore hole in sight.
my blog
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vbstenswick Posted 6:30 pm
18 Jul 2007
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JoshS Posted 10:19 pm
18 Jul 2007
As the other comments definitely point out well, there are different strategies that make radiant by far the best option, even when combined with passive solar and super-tight, energy efficient building envelopes and design.
And I agree about radiant and geothermal. There's an innovative geothermal installer in our area who designed a solar-assist component to the geothermal system (recharging the source side if I remember right).
This is one issue where Building Green just gets it wrong.
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moglig Posted 4:44 am
19 Jul 2007
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donnakay Posted 5:27 am
19 Jul 2007
We have already installed the laminate in the basement in our daughters room, but may order some of the under rug radiant heating for there.
I also have a historic storefront which is now my living room. Unfortunately we carpeted it before knowing about this option or knowing how flipping cold it would be in there. We were told that making the floor more even would cost over 10K, and trying to install flooring was going to screw up the location of the doors and all molding. At least the carpet makes the uneven floor less noticeable. Granted, for best results the floor would be nice and flat, but sometimes you just go for what works when you don't have an infinite budget.
(and yes, we have stopped and developed a long-term plan with an architect so we could work on this stuff in some reasonable order over time from now on...)
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spaceshaper Posted 8:52 am
19 Jul 2007
JoshS - have to disagree with your blanket disagreement with Building Green. Radiant floors have their place but they're not for everyone or every climate. The U.S. is a big country with many climate and microclimate variations. Slow response, high thermal mass radiant systems are ideal for areas with long predictable heating seasons but are problematic in places with humidity issues and fast unpredictable weather changes. And some folks (I'm one) find radiant floors just uncomfortable - makes our feet sweat.
It's horses for courses. Costs are always a factor. If you need to air-condition, you'll be putting in two parallel climate control systems, with two separate kinds of maintenance issues.
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JoshS Posted 9:15 am
19 Jul 2007
I definitely can see how my post left certain impressions open to interpretation, but I'm not arguing that radiant floors are for everybody or every climate.
I disagree with the essential reasoning behind Wilson's disagreement about radiant heating in certain climates, namely colder climates with greater numbers of heating degree days. It's written with the beauty of a true non-builder's thinking. :)
That said, other excellent strategies exist for such climates as well, not involving radiant.
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duchessrachel Posted 3:59 am
20 Jul 2007
It's so nice to come home to my apartment in the winter and lie on the toasty floors. Some of my friends will throw their blankets on the floor before work and then come home and curl up in the warmed blankets. At restaurants, it's so nice to sit on the heated floor, too. It's amazing. After living here, I can't believe how long it's taking the rest of the world to catch on.
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nadav Posted 4:43 am
20 Jul 2007
But I have built a house with a radiant slab-on-grade. It works fine, but it's not what I would do today, given what I've learned in the last 15 years about energy efficiency and climate change.
I think you're missing the key point here. Radiant floors are a wonderful way to distribute heat when you need a lot of it (so in Alaska--perhaps). They are overkill to distribute heat when you need very little, and in fact they don't work well in that setting, because they will either deliver too much heat, or they'll feel cold.
If you have drafty, leaky home, sure it will be more comfortable with radiant floors. But if you have the option to spend $8,000 on radiant floors, or the same on upgrading windows and air sealing, how could you possibly choose to invest in the floors? Either way, you get a similar level of comfort, and by upgrading the thermal performance of the home you reduce your heating bills dramatically. Even if you're rich enough that you don't care about the costs--how can you justify that choice today, in 2007, with the ice caps melting faster than anyone predicted?
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kaivalya Posted 4:49 pm
22 Jul 2007
Here in Central Europe, where I live, the waterpipes are placed in the walls underneath the plaster. The larger the heated surface- the lower the heat required in the pipes. If your house is well insulated ( also the floor ) this will keep your rooms constantly at the same temperature.
Traditionally we use tiled stoves. We have one in our house and I don't want to miss it anymore.
If it is well constructed it can heat your whole house, it needs little maintenance (cleaning every six years), it works for decades and doesn't depend on electricity.
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