radiant floor heating design
I (a professional Diy’er) installed a first floor radiant floor heating system that looks like this: 3 loops of 1/2 pex , each loop 250′ long. using a boiler as the heat source. I have the water mixed to 140 F. used double bubble with the reflective barrier as the only insulation. The basement is unheated. I live near albany,ny. I did not use the plates for heat transfer.(read that they were only good for noise making)
I ususally heat the house with a wood stove, but we had to leave for an xmas trip for 4 days. Set the house thermostat for 59 F while we were gone. When I checked my oil tank when I got home I used a little more than an 1/8th of a tank. About 70 bucks worth! The high and low temps were upper 30s and mid to upper 20s. warm for around here. where have I gone wrong?
More info: When the system is running I can feel heat leaking through the double insulation. The second floor is baseboard.
Replies
Hmmm. From what I've seen and been told, radiant floor heat requires full insulation under the floor between the joists, with particular attention paid to the rims. My supplier recommends *at least* 6" of glass or celulose. I never thought foil bubbles makes for good insulation and you seemed to have proved it by heating your basement. Also, my understanding is that the aluminum plates transfer the heat from the pipes to the floor material by conduction through a large contact area, allowing the floor to get warmer so it can radiate to the room. Without the plates, all you are doing is heating the air between the joists and relying on high air temp to heat the floor. Not particularly efficient, especially since the floor is probably a better insulator than your foil bubbles.
Mike Hennessy
Pittsburgh, PA
thanks mike. it seems pretty obvious the way you break it down. I was in the 'burgh for xmas. born and raised there. take it easy.
dave
there are different plates too. light floppy ones are better than nothing, but may have noise issues. heavy extruded ones are very powerful and, of course, more expensive, but are pretty hard to make noisy.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
redtoolbox,
How well insulated is your basement?
heat rises, it isn't lost untill it escapes. If the basemet walls are well insulated then the heat will rise, otherwise you are now heating walls to 70 degrees which before were at 55 or so.. heat will love to sneak out thru the walls.
I like plates for transfering heat. it will generally be quiet if it's continuous. If not then the two problems you experiance is noise and second abrasion.. the edge of each plate will abrade the pex as it shrinks and expands from the heat.. both can be delt with.
I use simple cheap aluminum flashing and a bead roller.. that way each joist is filled with only one piece so there shouldn't be a noise issue. IN addition I take a tool and roll the edge of the bead away from the pex radius the entry/exit. that way the pex movement relative to the aluminum won't be an issue..
If your basement isn't well insulated (look carefully around your joists) insulate it and it will improve.. if you would like to direct more heat up then you need to get some of that foil backed insulation and seal each joist bay. (or if you can spare the head room just cover all of the joists with it and then cover that with sheetrock.. (need to for fire code reasons)
MY bead roller didn't come with a large enough bead to hold the pex so I had a machinest make me one the size I need.. If I had to do it all again, I'd have bought the powered one instead of the hand cranked one.. But I'm getting lazy in my old age!
Heat does not rise (exclusively). Hot air rises. Heat is radiated 360 deg, including right down into that basement.
JD
we are saying the same thing, while heat does certainly radiate, it will eventually rise (the principle behind a hot air ballon) however as you say it also radiates, (which is why you must continuely reintroduce heat back into that hot air ballon or it will start to sink) Same with the basement the heat is now radiating and as it hits uninsulated basement walls with an R value of say.02 per inch it will as I pointed out, try to sneak outside rather than do it's job which is to warm up the house above..
If you insulate the basement walls you trap more heat into the building envelope.
thanks frenchy, I think I will use your bead roller idea on the flashing and add some r-19 to the bubble.
Noise comes from expansion, not typically plates touching. If you control your operation and water temperatures succesfully, you reduce expansion. If the tubing slides in the plate easily and has places to expand TO without hitting stuff and transmitting force laterally against plates, you reduce noise. If you use a PAP instead of a PEX, expansion is reduced.Or you can use a heavy gauge plate, which holds the pipe tightly enough that it can't move much, and eliminate the issue that way. While also dropping your water temps another 20 or 30 degrees in most "normal" cases.We used light plates for a long time, but in general I consider the trade up to extruded plates well worth it. If not, I don't use plates, because the load is so low it doesn't make much of a difference. This is admittedly not a common situation, but it happens, generally in warmer climates or superinsulated situations.and as another poster noted, heat does not rise. hot air rises. Many improperly insulated radiant installations are heating the basements below them to 70 or 80 degrees.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I live near albany. We have the foil bubble insulation under about 2,900 sf of floor. I don't think it is enough on it's own. I cut the amount of propane usage by 20% when I added r-19 fiberglass under the foil. My light gage metal plates don't make much noise. The water temp in the pex should be a constant temperature, or not have wide temp fluctuations to minimize expansion and contraction.
If I were to use the r-19 fiberglass i would get alot of mice nesting in it. do you have other ideas? thanks for your input.
Dave
How did you attach your pex to the subfloor? We use the copper plated pipe straps rather than the aluminum plates and have good success, they go up easy 12" OC with 1/2" hex head sheetmetal screws. We have no problems with mice in the R-19 either. Dan Holohan's book Hydronic Radiant Heating (http://www.heatinghelp.com) is my guide, I've given more than ten copies away to employees and clients. Simple fact is that with radiant you are buying your BTU's same as forced air, it's just the delivery method that is different. It's no miracle cure, you still need insulation, draft stopping, and common sense. The super cool thing about radiant is how well it interfaces with solar hot water. Because it is easier to heat cold water than hot you can use a radiant floor to keep your solar storage tank at 70 degrees and optimize the heat transfer from your collectors to your storage tank. You still need a demand water heater for a back-up but you maximize the BTU's transferred from the sun to your home.
My ceiling has 5/8" gyp. bd. in the basement. I have seen rigid foam insulation cut and placed between the floor joists. If I were to do it over again I would use the rigid foam. I am not fond of fiberglass.
redtoolbox,
Couple of points, to keep from abrading the pex where it goes in and out of the aluminum take a large phillips head screwdriver (because the shank is round) and roll it at a 45 degree angle at the entry of the bead. That does two things, it flattens the possibly sharp edgeof the bead and deforms it enough to make a slight radius.
Done properly It takes less than a minute to do. Don't forget the exit point too, that aluminum is shrinking and expanding with the temp differances relative to the pex. which is why we are concerned in the first place.
I'm not a fan of fiberglas insulation. It's ratings while labratory accurite don't reflect the real world. In the lab the R rating is calculated at 70 degrees.. as the temp differances increases the R rating becomes less and less accurite..
Fiberglas is not a good air infiltration barrier so air tends to move through it easily. (it's what they make furnace filters from) that air movement sorta defeats what you are attempting to do with the heat from your PEX. In a perfect situation each joist bay would be an air duct funneling heat upwards.. the c oser you can get to that situation the greater the heat transfer upwards would be.
I prefer rigid foam board insulation under the tubing.
Foil-faced polyiso is my first choice. Rip it ever-so-slightly wider than the joist bays on the table saw and pop them into the bays, friction-fit, right up against the heads of the tubing staples.
Heat travels from warm to cold, so more "r" under the tubing (insulation) than above the tubing (combined r-values of the subfloor, underlayment, flooring material(s)) will encourage your BTUs to go in the proper direction.
I prefer about 3 times the R under the tubing than above.
Don't forget to insulate the rim joists! Muy importante!
The bubble insulation? I have zero faith in those products when it comes to actual performance versus claimed performace.
Radiantly, Mongo
Heat migrates according to resistance. Less resistance, more migration in that direction. Your flooring is providing more resistance than the essentially useless bubble wrap, so most of the btu's will go to heat the basement, and that's likely not where the t-stat was. Did you observe the basement temp when you returned? If you add insulation, I'd prefer rigid to fg.
Edit: Or....read what Mongo wrote! Hey, Mongo, HNY.
Edited 1/3/2007 9:46 am ET by CloudHidden
Thanks, and back at you.Was down your way a couple weeks ago, I came so close to trying to contact you for a drive-by, but I haven't been on the forums much as of late.Hope all is well in that gorgeous concrete bubble of yours.Mongo
>I came so close to trying to contact you for a drive-byWish you had. I would have enjoyed that.