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Is whole house radiant floor heating effective in the real world?

Is whole house radiant floor heating effective in the real world?

Calling out to homeowners with radiant floor heating...

I am looking at constructing a new home in New England, specifically the metro Boston area. A large house approx 4,500 sq ft on 3 floors, I would like to use radiant floor heating throughout, mainly for comfort but secondarily for hopefully lower energy bills.

The house would be well insulated and my concern is that I am hearing of issues of radiant heat and well insulated homes. I have read online:

"When the heating load is very small, the radiant slab has to be maintained at no more than a few degrees above room temperature to prevent overheating, and this means that the slab isn’t likely to be warm to the touch. A slab maintained at 74°F (23°C) will be cooler than an occupant’s skin, so bare feet will conduct heat into the slab."

If this is true I'm not sure if radiant floor heat would be worth the extra cost over forced air. I am looking to create a comfortable environment especially not cold floors. Have people experienced this is in the real world?

BTW I am looking at a hydronic system, I know that an electric system will probably be too expensive to run. My real question is overheating a real problem in an energy efficient house? One where you can get the floors hot enough to feel warm as the house would be too hot and overheat.


Asked by Pawan Bajaj
Posted Sun, 01/19/2014 - 22:18


4 Answers

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Q. "Is whole house radiant floor heating effective in the real world?"

A. Yes, it is effective.

Q. "I would like to use radiant floor heating throughout, mainly for comfort but secondarily for hopefully lower energy bills."

A. Radiant floor heating will not lower your energy bills.

Q. "I'm not sure if radiant floor heat would be worth the extra cost over forced air."

A. You are right to be skeptical. If you want to improve your comfort, the best way to spend your money is to upgrade your thermal envelope (by reducing air leakage, installing more insulation, and buying better windows). Once you have improved your thermal envelope, it hardly matters how you heat your house.

Q. "Is overheating a real problem in an energy efficient house?"

A. Summertime overheating can be a problem, especially if you install too many south-facing windows or west-facing windows. You need to design your house carefully to address this issue.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 01/20/2014 - 07:35
Edited Mon, 01/20/2014 - 07:37.

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We've built (non-passive-solar) homes heated by radiant floors; they work very well. Since then we've gone to superinsulated homes, which, as Martin says, are very easy to heat -and cool - with substantially lower cost heating systems. The last radiant heated home I built like this was 3500 Sf and cost about $2,000/yr to heat; With our present methods it would be 1/3 to 1/2 of that annual cost. The key is to upgrade your envelope.

Answered by Bob Irving
Posted Mon, 01/20/2014 - 08:24

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Heat your master bath floor with radiant. Still a nice feature to wake up to.

Answered by aj builder, Upstate NY Zone 6a
Posted Mon, 01/20/2014 - 12:12

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As a general rule in new construction, for the cost of any radiant system more elaborate than PEX in a concrete slab, you buy more comfort (and energy savings) by directing that money on lowering the heat load.

Even though it's possible in a moderate-R house at a lower room temp with radiant floors than with other heat emitters, what studies have been done on this demonstrate that the vast majority of the occupants of said houses run them at the same room temp they would if the were using crummy fin-tube baseboard, eliminating most of the energy savings. What savings can be gleaned at the same temperatures is in combustion and system efficiencies of the boilers & distribution plumbing over a higher-temp hydronic system. Assuming best-case design practices for both, using modulating boilers under outdoor reset control we're talking at best a 5% fuel & power use reduction by going solely with radiant.

Ducted hot air has an energy use penalty over hydronic heat delivery for two primary reasons:

1: The thermal mass of air vs. water, and duct-impedances vs. plumbing resistances means delivering the same amount of heat with air takes several times the power use in air handlers than would be used by pumps in hydronic systems.

2: Even in the best well sealed Manual-D duct designs, the air handler pressurizes some rooms, depressurizes others, which drives outdoor air infiltration through the leaks in the building envelope, actually increasing the heat load whenever the air handler is operating. In "typical" new home duct designs & infiltration leakage it's on the order of a 10% hit in additional fuel use with the standard 2-3x oversized fossil burner with a single-speed air handler. With a modulating right-sized system these issues are reduced by a lot, but never completely eliminated. Air-sealing the house to under 1000cfm/50 can make a real difference on the size of the problem too.

Hydronic heat deliver using low-temp panel radiators a fraction of the cost of most radiant floor systems, is QUITE comfortable, more responsive than most radiant floors to changes in load, and has none of the ducted air delivery issues.

Ductless heat pumps are a small step down in comfort from there, provide very stable room temps, are POSSIBLE to right-size for a high-R house, and are quieter than all but the very best variable-speed ducted air solutions.

Answered by Dana Dorsett
Posted Mon, 01/20/2014 - 12:29

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