Radient heat question

[eriesigtau]

I have radient floor heat...1/2 pex with 2 runs per joist. No runs are longer than 175ft. I noticed in other homes, their floors seem warmer than mine and I have also noticed that from a cold start, it takes hours to bring my home up to temp. Most of my house has a 1" ruff cut subfloor with 1/2" oak hardwood floors. Some areas have tile and others have carpet but the hardwood is 75%. All the pex was hung with nail in pex clamps and then I installed R-11 fiberglass insulation under that (loosly against the pex). I have a mixing valve that reduces the the temp to the pex pipe from 180 to 140-150 (as I was instructed to prevent hardwood floor damage).

Does anyone have an idea why the heat is not transfering as fast as it should or is what I'm seeing normal?

 

[in hot water]

That is called a suspended tube installation. It transfers heat by convection currents in the joist bay. You need some space below the tube, don't allow the insulation to be tight against the tube. Air space for the convective currents to move heat energy.

It is very important that the joist bay ends be well insulated and sealed for infiltration. Spray foam then at least 6'' of insulation at the rim joist. Driving the energy thru that much wood flooring will be a tough go with this type of installation. Without a heat load calc it is a guess as to how well it will work. Maybe 15 BTU/ sq. ft output.

You may need to crank that supply temperature up. With the tube disconnected from the flooring I doubt you will overheat the top flooring. The goal is to keep the surface temperature below 85F to prevent un-comfortable conditions. Wood flooring cracks and shrinks more from moisture change then temperature. Keeping a proper humidity level is key to happy hardwood.

Check out www.ultra-fin.com I've used these heat transfer fins and they really help increase the output on a suspended tube install. I believe they have some tables to show output under various supply temperatures.

I'd also beef up that insulation below the tubing. Depending on the room temperature below you need more thermal resistance below the tube. 1" subfloor plus 3/4 hardwood is about an R 2.2 with carpet 2.6.

Heat transfer plates that actually fasten to the bottom of the subfloor will be the most powerful transfer mechanism. They transfer by conduction, like a pan on a burner, much better then air currents to move heat. They can be a bugger to retro-fit around nails, bridging, etc.

You might consider that a floor warming system, it would require some supplemental heat probably, especially on cold or design condition days.

hr

 

[EffectaBoilerUser (USA)]

I installed in-floor heat in 4 rooms of my house and I can feel the warmth in the floor itself.

I did a lot of research before installing the staple up in-floor heat system and there were 2 problems that kept being mentioned/repeated over and over:

1.) Make sure that when using 1/2" pex the maximum length of each loop is no longer than 300'.
2.) The use of heat transfer plates. although quite expensive, make the heat transfer rate much greater and the overall system much more comfortable/efficient.

I ended up going with the "heat link" brand of controller, manifold, heat transfer plates and tubing as per the heat link recommendations. I placed the Heat transfer plates over the pex tubing and stapled them directly to the OSB. I left 6" gaps between plates.

I took some photos with my Flir IR heat gun and have attached them to this post.

My system has been installed for 6-7 years now and it works great!

Brian

 

[eriesigtau]

I was unware that I needed to insulate the joist ends that well. I will revisit those areas and add some insulation. I'll also see if I can't lower the insulation some. Its not tight up against but its probably 1/2 to 3/4 up into the joist depending on the area. I was told the fiberglass is better than the reflective. Any truth to that? I have been experimenting with U channel alum snap on plates. I think Ive put up about 30 so far. Ill add some of those and crank the temp up to maybe 160? Thanks for the info.

 

[Sawyer]

Brian, do you have any hardwood floors?

We will shortly be doing a conductive heat plate/pex installation in the joist spaces below our hardwood living room floor.

 

[huffdawg]

I installed in-floor heat in 4 rooms of my house and I can feel the warmth in the floor itself.

I did a lot of research before installing the staple up in-floor heat system and there were 2 problems that kept being mentioned/repeated over and over:

1.) Make sure that when using 1/2" pex the maximum length of each loop is no longer than 300'.
2.) The use of heat transfer plates. although quite expensive, make the heat transfer rate much greater and the overall system much more comfortable/efficient.

I ended up going with the "heat link" brand of controller, manifold, heat transfer plates and tubing as per the heat link recommendations. I placed the Heat transfer plates over the pex tubing and stapled them directly to the OSB. I left 6" gaps between plates.

I took some photos with my Flir IR heat gun and have attached them to this post.

My system has been installed for 6-7 years now and it works great!

Brian

Hi Brian ,just curious what temps you are pushing through your pex lines to obtain those floor temps

Huff

 

[huffdawg]

Is your hard wood floor engineered hardwood or solid hardwood George. From what I have researched using solid hardwood isn't a good idea , but I imagine a few on here have done so. Would be interesting what the results are . I have some engineered redwood on top of a concrete over poor . works great no issues for three years.

Huff

 

[Fred61]

I place room temperature and comfort in separate camps. What made me put comfort up to the top of the list was my experience back several years ago when I was working for a living. I had an office with a big window that overlooked a workspace with fifty to fifty five women doing bench work for me. Although the temperatures were fairly constant, each worker had a sweater draped over the back of her chair. Those sweaters went on and off several times each day in both the heating and cooling season. The air handlers kept the area within one degree F but they could sense the cycling of the heating or cooling coils.

Since I got rid of my big place nine or so years ago to downsize into my little plastic house because I wanted to rid myself of the high costs and maintenance of a larger place in retirement, I've had a nail gun in my hand ever since. One of the many "improvements" was radiant floors. I went with Radiant Company in Barton Vermont which uses 7/8 pex as staple-up. All the improvements to my floors such as hardwood, porcelain tile and laminate were added to the top of the existing 3/4 inch sub floor plus 3/4 inch underlayment. Add 3/4 inch hardwood or cement board topped with tile and it makes a pretty thick barrier for heat. I'm running 140 degree water and is keeping the house at a constant 70 °F.

With the boiler and storage in the basement making heat and the low heat loss of the house, the circulators do not run very often with the mild winter we have had. With no call for heat because the thermostat is satisfied and other heat sources supplying heat, such as refrigerator, oven, etc. I feel cool when sitting around. My floors are not that warm. On the other hand, on the cold days, ie. hovering around 0 °F, I feel warm because I have the radiant circulating. If the body is radiating you are going to feel cool and if the radiant is coming into the body you're going to feel warm, even at temperatures lower than typical comfort temperatures. This is one reason I've been an advocate of using the °F scale for comfort measurement and the °C scale for scientific measurement of temperature.

The little 8X12 mud room that I pasted on the end of the rectangular main house has no heat sources below it and is isolated from the air flow of the main part of the house. We have alot of glass on one end and it has three walls exposed to the elements. In that space, I installed in-floor and it calls for heat several times per day. The floor is always warm mostly because of the frequent cycles to satisfy the thermostat. It's very comfortable it there, even though I keep the thermostat at 69 °F .

Pic below showing my pasted on mudroom.

 

[Gasifier]

I have noticed it makes a difference what type of bench work the women are doing as well. What?

 

[8nrider]

owens corning makes a r-13 fiberglass bat w a reflective paper, ideal for this application. i would not run anything over 140 if it is solid wood. there really should not be a reason to. the air space between the pex and insulation in very important, good luck

 

[Sawyer]

Is your hard wood floor engineered hardwood or solid hardwood George. From what I have researched using solid hardwood isn't a good idea , but I imagine a few on here have done so. Would be interesting what the results are . I have some engineered redwood on top of a concrete over poor . works great no issues for three years.Huff

Huff, it's solid hardwood. Yellow Birch.

 

[SmokeEater]

I have radient floor heat...1/2 pex with 2 runs per joist. No runs are longer than 175ft. I noticed in other homes, their floors seem warmer than mine and I have also noticed that from a cold start, it takes hours to bring my home up to temp. Most of my house has a 1" ruff cut subfloor with 1/2" oak hardwood floors. Some areas have tile and others have carpet but the hardwood is 75%. All the pex was hung with nail in pex clamps and then I installed R-11 fiberglass insulation under that (loosly against the pex). I have a mixing valve that reduces the the temp to the pex pipe from 180 to 140-150 (as I was instructed to prevent hardwood floor damage).

Does anyone have an idea why the heat is not transfering as fast as it should or is what I'm seeing normal?

I'm just installing a hydronic system after 30 years of heating with cordwood in a hot air furnace. Too much dust, mold, and bugs to suit us as we age. Anyway, I'm real new to this boiler business and don't really know if the system will work as I envisioned. I did get some good info on a company in VT called Radiantec and they have some real good reputation for radiant heat intall in the northeast. This photo will show their conduction plate transfer system installed under my tiled bathroom floor with 2" of concrete and 1" of wood. The pex is 1/2" and the plates cost about $1 each. I haven't "lit up" my pellet boiler as of today, but hope to soon so I don't know how this system will work. If I don't get enough transfer with the plates spaced 1 plate apart, I'll put up solid plating to add to the transfer. Next I plan to staple up foil bubble polyethylene insulation to reflect the heat back toward the floor.

Your system may not be properly transferring the heat energy to your floor without the conduction plates and the reflective insulation that will reflect the radiant heat (IR) back upwards toward your floor.

 

[Singed Eyebrows]

I have noticed it makes a difference what type of bench work the women are doing as well. What?

Hey, I clicked the left thumbnail & they... I mean it was the same size, lol. Good post Gasifier, made me laugh, Randy

 

[greynjaded]

Folks,
"Lurking" seems acceptable so this will be my "howdy do".
Curious if a black painted surface in contact with the radiant pex will affordably be a bit more efficient.
I've been procrastinating with an install of an Atmos DC40GS I got from Xenon in 2003. It's been sitting in the cellar since August '03. Have been keeping things warm with traditional woodstoves indoors.
Randy, I'll be getting specific questions together once I've gotten my act a bit more together. Trying to answer what I can from related topics and posts.
But at least a 1st post. Enjoy reading everything you guys comment on.

 

[heaterman]

Hot Rod nailed it as usual. We in the radiant business have been there done that and like he said, the system you have in place is going to drive about 15btu's/sq ft into your floor and the space above it. Heat transfer plates will help a lot but if you stay the way your are, try raising your system temp to 160-180* if your mix valve will allow. I have a few running that way and they do OK in a decently insulated home. You're heating with wood in the first place so the addition of plates is going to have minimal effect on your overall costs of operation.

 

[Singed Eyebrows]

Folks,
"Lurking" seems acceptable so this will be my "howdy do".
Curious if a black painted surface in contact with the radiant pex will affordably be a bit more efficient.
I've been procrastinating with an install of an Atmos DC40GS I got from Xenon in 2003. It's been sitting in the cellar since August '03. Have been keeping things warm with traditional woodstoves indoors.
Randy, I'll be getting specific questions together once I've gotten my act a bit more together. Trying to answer what I can from related topics and posts.
But at least a 1st post. Enjoy reading everything you guys comment on.

Welcome to Hearth, I've been through the baptism by fire, so to speak, with the Atmos & would be happy to try to help, Randy