heat transfer through existing floor

[all night moe]

I'm wanting to add radiant floor heat via pex and extruded aluminum plates. This house has 5 1/4 plank flooring with 3/4 hardwood in a couple rooms. I'm concerned if it is too much thermal barrier to be an efficient heat source, or just take to lengthy of time to heat up from a lower value?

Thoughts and advice appreciated.

 

[salecker]

I have read many times that radiant flooring should not be used under wood flooring.
I believe it's the wood that has issues with the heat.

 

[all night moe]

To clear this up, the heat transfer plates are nailed/stapled underneath a wood subfloor, then transfer heat through tile or carpet, and not recommended for hardwood floors? In modern homes we typically see a 3/4'' subfloor with the 3/4 hardwood finished floor on top.
I'm a quarter inch less but I understand wood being a poor heat conductor.

 

[all night moe]

I've already planned for CI rads for the 2nd floor. I can easily alter my 1st floor plans and use them there also. My dilemma is the kitchen.
It may have less than the 5 1/4 subfloor since it was added on around the great depression. The walls currently have no sheathing. Just the wood siding. Either way it does have a 3/4 chestnut finished floor. The chestnut needs replacement and I'm planning for reclaimed hickory. Absolutely gorgeous in my view. I could go with tile but the subfloor is most likely the same 5 1/4 as the joists are 18''OC or a bit more.

I have little wall space for the size of the room. I guess I could get CI rads in there. I have one bank of windows approximately 11' long, and one other double hung for a total of 2 rads. It is a large kitchen with a breakfast nook. Not sure of the square footage because of the cathedral ceilings.

I could do the tile with pex in-between sub and tile....... but my vision of the finished product is full steam ahead on that hickory.

 

[airlina]

I've already planned for CI rads for the 2nd floor. I can easily alter my 1st floor plans and use them there also. My dilemma is the kitchen.
It may have less than the 5 1/4 subfloor since it was added on around the great depression. The walls currently have no sheathing. Just the wood siding. Either way it does have a 3/4 chestnut finished floor. The chestnut needs replacement and I'm planning for reclaimed hickory. Absolutely gorgeous in my view. I could go with tile but the subfloor is most likely the same 5 1/4 as the joists are 18''OC or a bit more.

I have little wall space for the size of the room. I guess I could get CI rads in there. I have one bank of windows approximately 11' long, and one other double hung for a total of 2 rads. It is a large kitchen with a breakfast nook. Not sure of the square footage because of the cathedral ceilings.

I could do the tile with pex in-between sub and tile....... but my vision of the finished product is full steam ahead on that hickory.

Moe, you're in luck because I am your guinea pig for this application. This winters project was to add underfloor radiant to 3 rooms (kitchen, Dining room & living room) all on my 1st floor of a log home. I recently completed 2 of the 3 rooms and have them up and running as we speak. I used 1/2" Pex-Al-Pex tubing for the 2 loops (both around 200' of tube req.) with the staple up heat transfer plates and pipe spacing was on average 9-12" o.c. My floors are unusually thick at 2 1/4" (subfloor is 2"x6" tongue & groove pine, covered with 1/4" luan ply and finally a 1/2" thick finished oak wood top. This is about the worst scenerio you can have with a lot of R fighting heat transfer, and I knew I might not have a great result , but now that I walk around in my bare feet I can call it a success. I use a floor sensor (inserted in a drilled hole about 3/4 way thru underfloor) controlled thermostat that I keep set at 85 deg to achieve a top of floor temp of 76-78 deg on average as read with a temp gun. My biggest surprise has been that the radiant sips my precious wood fired BTU's from my 500 gal storage tank , very unlike my original conventional baseboard system , that gulps those BTU to satisfy the required load. I will not remove the baseboard emitters however I can keep them at a lower temp now and use the underfloor for the majority of my heat in the 2 rooms I have completed. By the way my mixed water temp to supply the loops is 140 deg. It is a system that I keep running from 3 am to 5 pm because it takes a good 2 hours to get the heat up to temp at top of floor. At night (5 pm to 3 am)the thermostat is set to 70. Bruce

 

[brenndatomu]

I think real wood floors are fine with radiant heat under them, as long as the water temp isn't too high...or maybe that's concrete (both?)

 

[all night moe]

Hi, Bruce.
I've been binge reading the boiler room for days, enhancing my knowledge of hydronics. You are one of the more informative fellows on hydronics. Thanks for piping in. I've learned a lot and I know I'll never stop learning.

There is a ventless LP heater on the wall of the kitchen. Useful for warm ups. I'm sure it'd be great to complement floor radiant in it's slower starts of temperature rise. If you find your results satisfactory, I'll continue with my original plan.

The LP heater is the only source of heat currently in the kitchen. It was put in by the previous owner. Before that forced air through one register and a wood cook stove. They have been both disconnected long ago. Even as a pair, they were far from adequate. This was the second kitchen in the house, established for the migrant workers of the farm. It is the only kitchen now.

I look forwards to your results.

 

[ihookem1]

About 10 yrs . ago I decided to put 1/2" pex every 8" in my basement . I did not staple so the pex touches the wood. I also did not use much of the aluminum plates. I used about 6" every 4' to staple the pex and keep it up , but most of the pex is not touching the floor. I did 1,000' of pex. I insulated with fiberglass bats , R11 and R13. I I keep the water at around 160 to 170 degrees. The heat does not transfer fast, but it transfers very even cause the heat has to go somewhere. I have the pex under some tile and that feels good. I also have it under thick carpet in the family room and 3/4" maple floor in the kitchen. The tile feels the best , the maple floor is fairly good and the carpet does not seem to help much . However, it is amazing how warm the carpeted floor is when I lay down on the floor. It is very noticeable then. The heat goes somewhere. The aluminun plates help get heat to the floor faster but not any better and I think the plates give more warm and cold spots. My EKO 25 boiler sits in idle most of the time so heat load is low. Te house stays at about 68 and the floor is warm.

 

[all night moe]

I think real wood floors are fine with radiant heat under them, as long as the water temp isn't too high...or maybe that's concrete (both?)

Concrete is an excellent heat bank, provided it's not loosing it's load into the ground.
Wood....not so much.

 

[all night moe]

About 10 yrs . ago I decided to put 1/2" pex every 8" in my basement . I did not staple so the pex touches the wood. I also did not use much of the aluminum plates. I used about 6" every 4' to staple the pex and keep it up , but most of the pex is not touching the floor. I did 1,000' of pex. I insulated with fiberglass bats , R11 and R13. I I keep the water at around 160 to 170 degrees. The heat does not transfer fast, but it transfers very even cause the heat has to go somewhere. I have the pex under some tile and that feels good. I also have it under thick carpet in the family room and 3/4" maple floor in the kitchen. The tile feels the best , the maple floor is fairly good and the carpet does not seem to help much . However, it is amazing how warm the carpeted floor is when I lay down on the floor. It is very noticeable then. The heat goes somewhere. The aluminun plates help get heat to the floor faster but not any better and I think the plates give more warm and cold spots. My EKO 25 boiler sits in idle most of the time so heat load is low. Te house stays at about 68 and the floor is warm.

Until your post, I haven't thought about installing between sub and finished floors. It's a thought since I'm replacing the finished flooring. Just have to keep the pex punctured free. Definitely leaning towards radiant floor.

Thanks, Hooker
Sled pulls I presume? Name suggests

 

[airlina]

Moe , Knowing what my limitations where with my thick floor I will tell you that I am satisfied with the results and will continue the project to finish with my living room floor next fall (with spring around the corner I've got lots of projects outside that I need to get too). Having said that and reading your post about redoing your finished floor , and you have the opportunity to lay the pex on the top of the subfloor (they actually now make subfloor plywood with the proper tube pattern layour routed in it , to make the job super simple. google "this old house radiant heat job".) this would produce a better result because you would have a better heat transfer and you could eliminate the transfer plates and underfloor insulation.

 

[all night moe]

Moe , Knowing what my limitations where with my thick floor I will tell you that I am satisfied with the results and will continue the project to finish with my living room floor next fall (with spring around the corner I've got lots of projects outside that I need to get too). Having said that and reading your post about redoing your finished floor , and you have the opportunity to lay the pex on the top of the subfloor (they actually now make subfloor plywood with the proper tube pattern layour routed in it , to make the job super simple. google "this old house radiant heat job".) this would produce a better result because you would have a better heat transfer and you could eliminate the transfer plates and underfloor insulation.

Thanks for the tip airlina. I wasn't even thinking about the pre router sub floor. Probably because I'm keeping the existing 5 1/4 sub floor. But there is plenty of space to raise mine up. The kitchen is incomplete from the previous HO. All new 5/8 sheet rock and insulation but no baseboard moldings yet, or door trims. Thanks for the advice.

 

[airlina]

a few pics from my job, tubing and transfer plates, reflectix insulation over tubes and brains of the system

 

[flyingcow]

I’ve had staple up radiant in my kitchen area for many many years. 2 layers of 3/4 plywood. That now has a Lowe’s rubber backed planked floating floor on top of the subfloor. That’s gotta be at least 3/8 thick? Possibly 1/2 inch?

My mixing valve is set at 135/140f. I have a probe just peeking up in a corner, and my thermostat to control the floor is usually at 74f.

I did insulate underneath with r -11. And that’s all you’ll need. Basically have more Rvalue than the floor. Rolls of r-11 was a quick install. Left apx 4 or 5 inches of dead air space. Early on I did not have the insulation there. Very noticeable difference once installed.

And there’s been debate on whether you need the aluminum plates. I used them but I really don’t think you need to. My daughters house does not have them and seems to work fine. Biggest thing is more Rvalue below than thru the floor. Drive the heat up.

The kitchen area is 25% of my first floor area. In mild winter/spring days that’s all we need for heat.

Plus we still have the existing baseboard when needed.

The radiant floor works great. Happy feet…Happy wife😊. Plus we’ve thrown the grandkids snowsuits on the floor to dry out. Doesn’t take long.

We do not have the radiant on the hardwood area. And that’s just because I haven’t done it yet. But our hardwood floor is 25 yrs old. So when/if I do it I’m not worried about tue floor.

So my 2cents is I think your floor thickness is fine.

I wouldn’t hesitate to do my install again.
I would suggest having at least one more person to help with pulling the pex. And don’t let the spool of pex get too loose. I almost had to take sedatives at one point🍻.

 

[ihookem1]

No Moe, I stapled up the pex under the 4x8 OSB. It works pretty good. The pex does not have to be touching the bottom of the sub floor neither. It can be 1/2" under it. The heat stays right there and heats up the floor evenly, maybe even more even that when aluminum flares are used.

 

[airlina]

For those of you that the transfer plates are not needed, google "hydronics and heat tranfer plates " on youtube. In this episode John Siegenthaler , who is a guru on all things hydronic and wood heat systems, will detail why they are so important . Watching this video was enough to sway me. Its all about the greater heat transfer and BTU efficiency you obtain with the plates over simply stapling up tube and for those of us that heat with wood boilers, we know how precious every BTU is. Bruce

 

[all night moe]

I am finding hydronic heating very interesting. I appreciate all the help, guys. I hadn't much of a plan, just a basic idea of what I wanted to do. Through all my more recent readings here, in the Boiler Room, I've a basic plan to follow now. I'd rather build a system on paper now, several times, before executing. Seems much cheaper .... lol

 

[flyingcow]

I am finding hydronic heating very interesting. I appreciate all the help, guys. I hadn't much of a plan, just a basic idea of what I wanted to do. Through all my more recent readings here, in the Boiler Room, I've a basic plan to follow now. I'd rather build a system on paper now, several times, before executing. Seems much cheaper .... lol

This site has a lot of info and good people to help n share with their experience.
I think it was 2006? Maybe 2007 when I joined this bulletin board. Gleaned a ton of knowledge. And in Jan of 2008 I fired up my gassifier for the first time. I burn year round. Replace 150 to 175 gals of oil with 1 cord of well seasoned firewood.

The Green room is another good place on this board.

Good luck

 

[mark cline]

Interesting information, before next winter , I’ll have my finished 3/4” maple floor on top of the subfloor at 9-12” between loops. I plan to use Gyp-Crete around the pex with 1x2””sleepers to attach the hardwood to the subfloor. I was worried about the temperature under the maple , but I was planning on 125F or less . Through this winter , just the basement floor at 84F , gave me air temperature of 68F. Then the heat coming up through the subfloor kept the upstairs from 45F to 55F , plenty warm to work and finally get the upstairs finished. I’ll have to use a minimum of 120F mixed boiler water because I also heat a 50 gal indirect water heater, my Econoburn 300 and 1500 gal of storage will easily heat the 3500 sq ft log home which includes the basement.

 

[peakbagger]

If you look at John Siegenthalers recommendations, he does not recommend this approach on new installations as the layers of wood means having to run higher loop temperatures which impact the effectiveness of storage and the response of the heating. He is much more an advocate of radiant behind walls and ceilings and has the numbers to back it up. From an efficiency goal, the lower the loop temps the better the system efficiency. The trade off obviously is access and putting the tubing under the floor is generally a lot easier than behind a wall. I have known a few folks who have done radiant ceiling and wall panels and they said they worked very well with low loop temps. Unlike convective heat flow which rises, radiant is line of sight so a panel up on ceiling can heat a floor.

If folks insist on radiant flooring, is generally recomended that a floating laminate type system is the better option.