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BackPage Primer from Environmental Building News
February 1, 2010
Radiant Floor Heating:
Wrong Choice for Green Homes?
DISCUSSIONSReader-contributed comments related to Radiant Floor Heating: Wrong Choice for Green Homes? - EBN: 19:2. Comments are listed with newest at the top.
A general comment on how radiant floor systems work
Posted by
Peter Yost
on Feb 5, 2010, 11:25 AM
This is a great exchange of insights on radiant floor systems. I just wanted to add two:
1. On average, radiant floor heating systems deliver only about a maximum of 60% of their heat by radiation; the rest is mostly by convection.
2. The above ties into claims of reduced operating air temperatures as an energy efficiency element of radiant floors. You can't really KEEP air temperatures depressed if you have a slow-acting radiant system that is heating only 60% by radiation; the air temperature rises as the floor heats by convection. When radiant floor heat first comes on, there may be some higher mean radiant and lower air temperature but in steady state, the mean radiant and air temperature are going to be very nearly the same. The only way you can KEEP the air temperature depressed is if you have a really leaky home, but that seems overall counterintuitive and counterproductive.
There is no denying the thermal comfort of radiant floor heat, but Alex is right: if you have a limited number of dollars to spend on your heating system and building envelope, investing in a better envelope instead of an expensive heating system makes the most sense, just about regardless of climate.
This is a great exchange of insights on radiant floor systems. I just wanted to add two:
1. On average, radiant floor heating systems deliver only about a maximum of 60% of their heat by radiation; the rest is mostly by convection.
2. The above ties into claims of reduced operating air temperatures as an energy efficiency element of radiant floors. You can't really KEEP air temperatures depressed if you have a slow-acting radiant system that is heating only 60% by radiation; the air temperature rises as the floor heats by convection. When radiant floor heat first comes on, there may be some higher mean radiant and lower air temperature but in steady state, the mean radiant and air temperature are going to be very nearly the same. The only way you can KEEP the air temperature depressed is if you have a really leaky home, but that seems overall counterintuitive and counterproductive.
There is no denying the thermal comfort of radiant floor heat, but Alex is right: if you have a limited number of dollars to spend on your heating system and building envelope, investing in a better envelope instead of an expensive heating system makes the most sense, just about regardless of climate.
Radiant floor heating in cold climates
Posted by
L. Frederick Dure
on Feb 5, 2010, 10:07 AM
We installed the Wirsbo floor tubing in a 3 in concrete slab elevated floor in our Alaska bush (off grid location), but have not deployed the system. The intent was to analyze options to power the system in the future. Anyway, I wonder if the potential negative effects mentioned in the article are pertinent to cold climate environments where there is minimal passive (thermal) gain during low sun winter months?
We installed the Wirsbo floor tubing in a 3 in concrete slab elevated floor in our Alaska bush (off grid location), but have not deployed the system. The intent was to analyze options to power the system in the future. Anyway, I wonder if the potential negative effects mentioned in the article are pertinent to cold climate environments where there is minimal passive (thermal) gain during low sun winter months?
Energy Efficiency
Posted by
John Swearingen
on Feb 4, 2010, 06:15 PM
We have similar results to Gary in his area with our strawbale homes. In a 2800SF home in Sonoma, they use the heat only 3-4 times each winter.
However, these are mild winter climates that require minimal heat anyway. In the Sierra foothills and areas with little direct gain in winter, when heating is more continuously called for, the radiant floors are more practical.
Our biggest concern in design is the balance of underslab insulation. Since we design primarily for cooling loads, which are generally greater than heating loads in most areas of California, we appreciate the significant boost that we can get from earth coupling with minimal or no underslab insulation, and that creates a thermal sink in winter.
We have similar results to Gary in his area with our strawbale homes. In a 2800SF home in Sonoma, they use the heat only 3-4 times each winter.
However, these are mild winter climates that require minimal heat anyway. In the Sierra foothills and areas with little direct gain in winter, when heating is more continuously called for, the radiant floors are more practical.
Our biggest concern in design is the balance of underslab insulation. Since we design primarily for cooling loads, which are generally greater than heating loads in most areas of California, we appreciate the significant boost that we can get from earth coupling with minimal or no underslab insulation, and that creates a thermal sink in winter.
Radiant Floor Heating: Wrong Choice for Green Homes?
Posted by
A. George Beeler
on Feb 4, 2010, 06:10 PM
I have stopped using radiant heat for both residential, school & commercial buildings for all of the reasons that you state in the article plus:
1 The slab is not able to store heat for passive solar heating if it is already warm when the sun's heat is available.
2 During spring & fall when the days are warm but the nights are cool, the warm slab from morning radiant heating persists into the afternoon and interferers with passive cooling.
I have stopped using radiant heat for both residential, school & commercial buildings for all of the reasons that you state in the article plus:
1 The slab is not able to store heat for passive solar heating if it is already warm when the sun's heat is available.
2 During spring & fall when the days are warm but the nights are cool, the warm slab from morning radiant heating persists into the afternoon and interferers with passive cooling.
Energy Efficient Houses
Posted by
Gary Pugh
on Feb 4, 2010, 01:55 PM
I am a SIP builder in northern CA. My clients that put in radient floor systems report that it rarely comes on.
Case 1 - 750 SF Granny in Santa Rosa. they have to leave the PILOT light out in the fireplace or house gets to warm, radiant on only occaisopnly & then only a few minutes at a time.
Case 2 - Geyersville CA, SIP house, rearely gets below 64 degrees, hardly ever comes on even when house is left for 3 weeks in winter.
Case 3 - Sebastopol, CA 850 SF guest house, gas for radiant boiler = less than $20/ month
Case 4 - Lake county, 120 heat wave, house stays at 80 or below, no AC. When the fireplace was burned had to open all windows!!
Simply stated, save the money for something else IF you are wise enough to build with SIPs. No matter where you live.
Gary
I am a SIP builder in northern CA. My clients that put in radient floor systems report that it rarely comes on.
Case 1 - 750 SF Granny in Santa Rosa. they have to leave the PILOT light out in the fireplace or house gets to warm, radiant on only occaisopnly & then only a few minutes at a time.
Case 2 - Geyersville CA, SIP house, rearely gets below 64 degrees, hardly ever comes on even when house is left for 3 weeks in winter.
Case 3 - Sebastopol, CA 850 SF guest house, gas for radiant boiler = less than $20/ month
Case 4 - Lake county, 120 heat wave, house stays at 80 or below, no AC. When the fireplace was burned had to open all windows!!
Simply stated, save the money for something else IF you are wise enough to build with SIPs. No matter where you live.
Gary
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I do think there is a point here with super high performance smaller homes. If every home could be heated with a match we wouldn't even need to be having this discussion but unfortunately even many green homes still have a significant heating load, especially in colder climates.
1. I think the IAQ improvement with having no ductwork is a big plus that is not mentioned. After all, green building is not just about energy.
2. One of the biggest benefits for radiant floor is the ability to tie solar thermal in for heating climates. In North Carolina we have a 35% tax credit for solar space heating. This makes the finances a little different compared to a high efficiency heat pump with no tax credits available.
3. Our trick here in a mixed humid climate is that it doesn't offer dehumidification so you have to end up with an additional system if you want to dehumidify.