I stapled up 750' of 1/2" pex on the bottom of my floor. It is under the whole living room , kitchen, and master bathroom floor. It gives the house a very warm feel and I can't quite explain what I mean,, just more comfortable. My question is though, is that many say it's more eficient than forced air. I am looking to see if anyone has done this and have you seen less wood usage sinse going to hydronic floor heat?? One other thing. I went 8" OC under the carpet but went 16" OC under the wood and ceramic tile in the master bath. The 16" OC works enough to take the chill off the floor but not much more.
hydronic staple up floor for efficiency.
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Well, all i can say, going from my old house to my new house, I'm comfortable at 65 in the new house, where in the old house it'd have to be 72 at least.
bmblank, that seems about right for me. We were @70 and 66 seems about the same temp. It must save fuel, some websights ( mostly hydronic parts supply stores) say it's 25-40% more efficient. That seems hard to believe though.
logger6644
Member
A couple of basics about heating systems. Forced air is just that, it heats the air and circulates it through the space. You have temperature gradients ...hot air rises and these gradients and air movement have an impact on comfort meaning you need a higher setting to feel warm. Radiant heat works not by heating the air but by heating objects, including you by radiating the energy from the warm floor to you. You will feel more comfortable at a lower temperature. Just a word on fin tube wall heating. This is a convection heating and depends on setting up a convection current of hot air across the units. In order to set up this convection, higher temperatures are required, around 160 F to operate properly. In general it has the same drawbacks as forced air with the temperature gradients and heat being conducted through the air. Radiant floor heat generally requires only 110 to 120 to function properly. One of the main reasons radiant is more efficient is because of the comfort level at lower temperatures and the uniform air temperature whether at the floor or ceiling. The higher air temperatures of forced air and fin tube systems lead to higher heat losses because of higher temperature differentials at ceiling and roof levels. It is not 25 to 40 percent though, maybe 10 or 20 at most.
Now a couple of comments on radiant tubing for floors. In general 300 feet should be your maximum loop length. A zone can have more than one loop but they should be of equal tubing length. Staple up on 8" is fairly standard coverage, 16" not enough. You should have aluminum plates that snap around the tube to improve heat transfer rates and insulation below the tubing to direct the heat up. Check out the websites for radiant heating for more more complete info on design issues as there is a lot more to it than I can go into here.
Now a couple of comments on radiant tubing for floors. In general 300 feet should be your maximum loop length. A zone can have more than one loop but they should be of equal tubing length. Staple up on 8" is fairly standard coverage, 16" not enough. You should have aluminum plates that snap around the tube to improve heat transfer rates and insulation below the tubing to direct the heat up. Check out the websites for radiant heating for more more complete info on design issues as there is a lot more to it than I can go into here.
Basic physics of radiant heat.
Here's the first fact. Physiologically speaking the human body is most comfortable when your feet are warmer than your head. That is exactly what a radiant floor does and conversely, exactly the opposite of forced air heating. That is a proven medical fact which you can look up via Google. Or Robert Bean's website......
The main difference between say...65* with true radiant heat (large mass at slightly elevated temperature) vs 65* with a forced air system is what radiant does to everything in the room. I have a classic example going on right now in a 9,000 sq ft church building that is under construction. The building is 90x100 with ceiling height of 27' at the peak. The building is running at 60-61* and the drywall finishers are grumbling that it feels like it's 75* in there. I took my IR thermometer with me to check it out and showed them what the temp really was. (there are no thermostats as of yet)
The floor was running between 68-73*, all the walls, interior and exterior, the doors, the ceiling, everything in that building is pegged between 58 and 63*. If we were heating it with forced air we would find temps at the peak of the ceiling in the 80* range while it would feel like a chilly 60 down on the floor. I would guarantee that the exterior walls would read 10* less than the air temp.
What happens in a radiant heating system is that the energy emitted, by the floor in this case, does not actually heat anything until it strikes an object. Exactly the same way that the sun heats the earth after that energy travels 93MM miles through space that is -400*F.
Heating objects such as doors, walls, ceilings etc has the effect of raising the Mean Radiant Temperature (MRT) of the room.
The rate at which any object or body loses heat to its surroundings is directly proportional to the difference between that body and the objects or space around it. The greater the difference the faster it loses heat regardless of what the air temperature may be. This is why you feel "colder" when walking down the frozen food aisle in the supermarket even though the air temp is usually always near the same as the rest of the store. You are surrounded by cold objects so your skin loses heat at a faster rate.
When a radiant floor heats all the objects in a room including furniture, walls, pictures, bookcases, desks, etc to the same temp the MRT becomes very stable. Your skin does not lose heat as fast if the walls are 65* as opposed to 50 like they would be in a system using heated air to create the illusion of warmth.
As to the energy efficiency of a radiant floor system the church is a good example. Before we got the radiant floor fired up we had 240K btu of forced air heat running in there to keep it warm. I would say run time totaled probably 14-15 hours out of every 24. The boiler we have in there now is a gas fired modulating type. After the initial start up period to get the floor up to temp (it was 40-46*) the boiler rarely gets off minimum fire which is about 80,000 btu. It is averaging about 16 hours per day of run time according to the info on the control. Do the math on that.
Here's the first fact. Physiologically speaking the human body is most comfortable when your feet are warmer than your head. That is exactly what a radiant floor does and conversely, exactly the opposite of forced air heating. That is a proven medical fact which you can look up via Google. Or Robert Bean's website......
The main difference between say...65* with true radiant heat (large mass at slightly elevated temperature) vs 65* with a forced air system is what radiant does to everything in the room. I have a classic example going on right now in a 9,000 sq ft church building that is under construction. The building is 90x100 with ceiling height of 27' at the peak. The building is running at 60-61* and the drywall finishers are grumbling that it feels like it's 75* in there. I took my IR thermometer with me to check it out and showed them what the temp really was. (there are no thermostats as of yet)
The floor was running between 68-73*, all the walls, interior and exterior, the doors, the ceiling, everything in that building is pegged between 58 and 63*. If we were heating it with forced air we would find temps at the peak of the ceiling in the 80* range while it would feel like a chilly 60 down on the floor. I would guarantee that the exterior walls would read 10* less than the air temp.
What happens in a radiant heating system is that the energy emitted, by the floor in this case, does not actually heat anything until it strikes an object. Exactly the same way that the sun heats the earth after that energy travels 93MM miles through space that is -400*F.
Heating objects such as doors, walls, ceilings etc has the effect of raising the Mean Radiant Temperature (MRT) of the room.
The rate at which any object or body loses heat to its surroundings is directly proportional to the difference between that body and the objects or space around it. The greater the difference the faster it loses heat regardless of what the air temperature may be. This is why you feel "colder" when walking down the frozen food aisle in the supermarket even though the air temp is usually always near the same as the rest of the store. You are surrounded by cold objects so your skin loses heat at a faster rate.
When a radiant floor heats all the objects in a room including furniture, walls, pictures, bookcases, desks, etc to the same temp the MRT becomes very stable. Your skin does not lose heat as fast if the walls are 65* as opposed to 50 like they would be in a system using heated air to create the illusion of warmth.
As to the energy efficiency of a radiant floor system the church is a good example. Before we got the radiant floor fired up we had 240K btu of forced air heat running in there to keep it warm. I would say run time totaled probably 14-15 hours out of every 24. The boiler we have in there now is a gas fired modulating type. After the initial start up period to get the floor up to temp (it was 40-46*) the boiler rarely gets off minimum fire which is about 80,000 btu. It is averaging about 16 hours per day of run time according to the info on the control. Do the math on that.
I see a congregation very happy to be using all that saved money for alot of good work for the community. Good examples too of the why it feels warmer/colder issues.
Bret Chase
Minister of Fire
radiant really needs a large thermal mass to work well, IMHO.... and if you've got a 750' loop... that is way, way, WAAAAAAAAY too long. should be 3 250' loops.
for me... unless I was putting 2" of gypcrete on the floor..... I wouldn't even consider just stapling pex to the underside of the subfloor...
for me... unless I was putting 2" of gypcrete on the floor..... I wouldn't even consider just stapling pex to the underside of the subfloor...
Good stuff, heaterman!
One of my favorite sites with tons of great reading. More about radiant myths and facts here: (broken link removed to http://www.healthyheating.com/Radiant_Mythology/Radiant_Floor_Heating_Myths_.htm#.UVJcJxysh8F)
Noah
One of my favorite sites with tons of great reading. More about radiant myths and facts here: (broken link removed to http://www.healthyheating.com/Radiant_Mythology/Radiant_Floor_Heating_Myths_.htm#.UVJcJxysh8F)
Noah
logger6644
Member
Heaterman did a great job explaining the way radiant heat works. I designed it into my house and workshop because of it's obvious benefits. In new construction, embedding the tubing in a slab or gypcrete on top of the floor is the way to go and that is how my house and shop are designed. Retrofitting in old construction usually makes these methods impractical, hence the tubing under the floor. Not optimal but definitely doable as long as it's done right, with aluminum distribution plates and insulation below and proper loop lengths.. You don't have the leveling effects of the thermal mass but the physics still work. We keep our thermostats at 67 or 68. 61 for a church is fine because of all the people gathered in one place but would be a little cool for most people in their home.
Brett Chase, I have a 250 ft run, a 500ft. run. The reason I put such a long run on is cause I didn't want much heat going to where the end of the 500ft run was. It's under the master bath that we use 1/2 hr a day. It is just enough to keep the chill off the floor but not use a bunch of BTU's up so it works good. The start of the 500ft ru is where we spend tons of time so that is where most of the BTU's end up and needed cause it's carpet. Heaterman, that makes sense. Hope the church goes real well. We are building a church and are going with hydronic heat too. And tell tell thaose drywallers to quit their whining. ( I can say it, I'm a drywaller too.) ( They do complain a lot don't they,,, )
Bret Chase
Minister of Fire
Heaterman - great explanation. How many customers eyes roll back in their head when you get about half way threw that explanation. The interested one's listen to every word and always come up with a question that there isn't an easy answer for. The others zone out. Current project -- The lady of the house leaned up against her new heated shower wall -- winner winner chicken dinner
That's thermodynamics she understands.
That's thermodynamics she understands.
Hey Bret,
I am running a low mass radiant floor system (above the subfloor) in my house and I have to say, it works great! Low temps, constant circulation, outdoor reset and super comfortable.
I considered pouring a thin slab over the subfloor to take advantage of lower supply temps and save some cost using concrete as the finished surface (acid etched). I really like the look, but in the end I decided against it for the hardness factor. Concrete *can* be brutal on the feet, knees, hips and back, especially for people like my family that like to spend a lot of time barefoot.
Regardless of thermal mass, radiant energy transfer is all about the temperature difference between the emitting surface and the objects that the surface can "see", as well as the emissivity of the warmer surface and the absorptivity and reflectivity of the cooler objects.
Kind of crazy to think that radiant energy isn't even heat until it is absorbed by an object.
Noah
The problem with long runs is while you run out of heat, the long pipe also cuts the flow severely. I've got some waaaaay too long of runs in my shop due to being in a crazy rush when pouring the slab and reading the wrong table of friction loss.
later calced that I'd need something like 54 ft of head to get 1 gpm flow in one of the loops and it was spaced at 1 ft per 1.5 ft2 of slab (designed for only 50 F with striping permited in the shop). The living area wasn't as bad "only" about 700 ft loop but required the highest head pump made so I broke into the slab and split my loops in half to 350 ft.
The shop loops will be 600 ft after splitting, still won't be able to maintain 50 F in the air space the 2 weeks of coldest weather. Let that be a warning to others out there!
later calced that I'd need something like 54 ft of head to get 1 gpm flow in one of the loops and it was spaced at 1 ft per 1.5 ft2 of slab (designed for only 50 F with striping permited in the shop). The living area wasn't as bad "only" about 700 ft loop but required the highest head pump made so I broke into the slab and split my loops in half to 350 ft.
The shop loops will be 600 ft after splitting, still won't be able to maintain 50 F in the air space the 2 weeks of coldest weather. Let that be a warning to others out there!
Bret Chase
Minister of Fire
Thermal mass is exactly the same as storage for a gasser boiler..... it evens out everything... the only downside to a large mass is warming it the first time.... it can take upwards of a 1000 gallons of propane to get 250 yards of concrete up to temp the first time....
Yes, radiant will work without a large mass..... but with a large mass... it just works better.
There is a place for high, medium, and low mass radiant. High mass is slow to respond and slow to ramp down. I would certainly use an outdoor reset control on a high mass system. Better yet a wifi thermostat like Ecobee that constantly gathers weather data and can anticipate a cold or warm condition and respond accordingly.
The medium mass systems like thin slab or gyp pours are another good option. Gyp offers sound and fire benefits also and is nice for retrofits. Tile over gyp can be a bit tricky, gyp does not like to get wet.
In my climate with frequent and wide temperature swings the low mass radiant works great, it can even be set back 3- 5 dergees and respond quickly.
Every system has pros and cons, it depends on your application and expectation.
A shop with a slab is a no brainer for in-floor radiant. Cold concrete is a real energy drainer to work on all day.
Mixing systems is another concept, add some panel rads for the shoulder season heat, before you flywheel up the slab.
Dunno, 70* is 70* to me. Doesn't really matter if it's from the floor heat in my house or the wood stove. I guess because of decent insulation?
I live with low mass radiant systems in every room but the bathroom, where we used Gypcrete to level the floor.
Given the low heat load, things work fine. We actually never use the bathroom floor which feels relatively warm in the winter.
I
On the other extreme, we once did a very high mass radiant system with tubing buried in 2' of sand underneath a slab.
It idea was to store solar heat.
It worked, but not really well.
The one good thing (I think) was that if the back up system which was propane went out (and it did--always around Christmas morning--resulting in a Christmas visit from Tom!) the homeowners did not realize it for literally days.
Would consider doing it again, with some changes. Maybe, with someone else on call for the holidays.
Given the low heat load, things work fine. We actually never use the bathroom floor which feels relatively warm in the winter.
I
On the other extreme, we once did a very high mass radiant system with tubing buried in 2' of sand underneath a slab.
It idea was to store solar heat.
It worked, but not really well.
The one good thing (I think) was that if the back up system which was propane went out (and it did--always around Christmas morning--resulting in a Christmas visit from Tom!) the homeowners did not realize it for literally days.
Would consider doing it again, with some changes. Maybe, with someone else on call for the holidays.
Not exactly the same, IMO. Here is why: concrete has a specific heat of .2 btu/lb/
, water has a specific heat of 1 btu/lb/. A concrete slab in a home is not going be very comfortable with a 
T of more than about 10,and that is pushing it. A thermal storage tank(water) can utilize a T of 70+ in a lot of cases . Lets look at a 1000 sq ft slab vs 1000 gals with these approximate usable Ts.Concrete slab:1000 sq ft x 6" thick=18.5 yds x 3900 lbs/yd=72,150 lbs x .2 btu/lb/
= 14,430 btu/ x 10 = 144,300 btus storedWater: 1000 gal x 8.33 lbs/gal =8330 lbs x 1 btu/lb/
= 8,330 btu/ x 70 =583,100 btus stored.Please, anyone, feel free to check the math-I ain't proud!
That said, I understand concrete can be a necessary structural component, as well as a very good low temp emitter and good thermal mass when passive solar is in the equation. But I maintain that living on concrete, even if it is warm, can be a painful experience for some people. It is just not very forgiving on the body and I believe people need to be aware of this trade off.
By the math, as I understand it, it should take no more than about 70 gallons of propane to raise 250 yds of concrete 30
. Not sure where the 1000 gallons came from but I suspect this here interweb!
Noah
Bret Chase
Minister of Fire
By the math, as I understand it, it should take no more than about 70 gallons of propane to raise 250 yds of concrete 30
Noah
a 1000sq ft slab???? lol.... I deal in the 5,000 to 25,000 sq ft range... hundreds of tons of concrete.
Nope, try again.... it was a 75X150' building I put up in 2001-2002. The new boiler was modern for the time... 6" fiberglass in the walls, 6" fiberglass in the roof.... standard metal building stuff... for the time. The building burned through a 1000 gal tank of propane (to be absolutely accurate... ~850 gal of propane) in the first two days, bringing the slab up from below freezing to operating temp... I remember the abject panic of the owners on the third day.... but once the slab was warm.... the building became very inexpensive to heat.
Bret Chase
Minister of Fire
In late august here, a 50 degree temp swing from low to high is normal.... The yearly swing is about 110 degrees... systems with an outside ambient sensor can be a godsend... esp with heating units with a variable firing rate...
With my floor heat (4" slab in house, 6" in garage) I can easily go 24hrs before the house starts loosing temp, even at -10* temps outside. The downside though is it takes about that for the house to be warmed up as well.
I'd love to have a small forced air system as well for fast heat. Perfect when just need to get the chill out and that it's... like the summer on a 50ish day. Now that I have a solar electric system, I keep a few plug in heaters available. More or less free heat.
I'd love to have a small forced air system as well for fast heat. Perfect when just need to get the chill out and that it's... like the summer on a 50ish day. Now that I have a solar electric system, I keep a few plug in heaters available. More or less free heat.
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