Radiant Floor on top of Subfloor
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Does anyone have experience with installing a Close Radiant heat system on top of existing subfloor (no access to floor joists)? We will install hardwood on top of that. The sunroom is 40′ long, and system will be 1 zone with 3 circuits. Heat source is an On-demand water heater. I am looking at Radiantec or Radiant Floor for supplies, both out of Vermont, but they have somewhat conflicting information about the install.
I’m looking for thoughts on how to to bring supply and return lines to the manifold. Did you use pex or copper? Location of manifold? For laying the Pex: did you use narrow sleepers with fins, or larger sleepers with a void of air, or filled with sand? Any tips on the install is appreciated! Thank you, Kurt
Replies
Dammit, I wrote a long history of the radiant floors I’ve done and wouldn’t you know it.......
All of it crapped out.
So I will come back to this and try again if you don’t get more answers.
/(#$=)*=(#;.,)’six!;+;*/cv,m.lkkhiuhhv;c#$&=+ hang here!
Any and all advice welcomed
Hang in there, taking care of some snow.
Alright, I’ll forget the lengthy reply.
I’ve done several radiant jobs, most in concrete, a couple in gypcrete over slab and one similar to Steve’s.
We had several rooms opened up and an addition to bring into the floor plan. The original hose we included bringing up an airing roof deck closed in. A lot of shimming and framing to make one good plane.
So over all the added or existing sub floors we did channels for the hose as Steve showed. Ripped osb to size, I believe we stacked rips and routed the curves using a jig, the end drops were used to finish the curve.
Htr contractor installed the hose and aluminum plates. His home runs went to a copper manifold and supply in a closet (warm coats).
Installed solid click lock floating wood floor. A heating company and flooring approved “pad” under the hardwood. Entry and bath were tiled and the transitions and underlay for those worked “no trip”.
Beautiful tedious job that provided new heat to the formerly unheated portions as well as the original replacement of basebd heated areas.
Appreciate the reply! What is your heating source and apprx size? If it’s in a coat closet manifold and boiler/water heater must be compact? Thanks! Kurt
Just the manifold with supplies coming up from a boiler in the basement. Whole rest of house house was HW basebd.
I've done it in a 3000 sqft home.
1) I purchased 3/4" plywood at a big box store, and then helped the store associate rip it into 7" wide strips using their panel saw. This was a HUGE time saver. I wasn't charged anything extra for this, but I did give the associate a tip.
2) Using a jig saw I made radius ends on the strips as needed. And then I cut half circles on on what I will call "end caps". I don't remember the size for the half circle on the end cap, but I believe it works out to a 9" diameter.
3) I laid out the 7" wide strips according to my layout plan, leaving a 1" uniform gap between each strip. Cut and use the end caps as needed so that you stay on layout and also provide a supply and return path to the manifold. Nail the strips down with the appropriate size ring shank nails. I also put a bead of adhesive between the subfloor and the strip. I don't believe that would have been necessary; however, I do not have any squeaks in my floors.
4. I used lightweight and relatively inexpensive preformed aluminum heat transfer plates. They fit between the 1" gap between the plywood strips.
5. I used 1/2" pex-al-pex, it fits snugly into the groove of the transfer plates. After the pex was guided into place I then sparingly fastened the transfer plates using short wide crown staples. Keep in mind the flooring will clamp the plates between the plywood strips and the flooring.
6. Now fasten the hardwood flooring to the plywood strips, just as you would in any normal application. You can use prefinished or do the sanding/finishing afterwards. I've also fastened 1/4" cement board to the plywood strips and then laid tile. If you do this, use thinset between the radiant layer and the cement board.
7. I used 3/4" oxygen barrier pex as supply lines to the manifolds.
8. I find this to be a quick reacting radiant floor. Meaning it gives heat rapidly, and without the flywheel effect of a cement or gypsum slab.
Last, I'd advise checking carefully into using an on demand water heater as your heat source. I recall some negatives about this. Keep in mind you're only raising the temp on your water by maybe as little as 10 degrees (a 10 degree delta is common in my system). An on demand water heater is designed to raise the water temp by not less than 50 degrees.
Best of luck. Steve
P.s.: The attached pics were taken by my spouse and more focused on the kids than the floor install. But they are all I have.
Steve, excellent reply and the pics are helpful. Do you have a pic of your heat source (boiler or water heater?) and the gages, expansion tank, ect? Also, where did you get the heat fins? Do you have a specific one you recommend? Kurt
nstead of using plywood or any of the mixed concrete type products, could the cement board that is used for tile backing be used in this type of application? My thinking is that because it should have the same type of thermal mass as gypcrete etc., it would work. Am I off base?
Edit My Post
Floating hardwood or are you nailing it off? Are you intending on using the aluminum plates as well?
Why do you think you need more thermal mass?
Increasing the thermal mass will not make much difference unless the floor is heated by some other intermittent source ( sunlight?), and you wish to store energy for off periods.
Concrete transmits heat better than wood, helping the distribute the heat evenly. Cement board is porous, about 1/2 the weight of concrete or a packed mortar bed, so not sure how the cement board would behave.
I was going to screw the cement board to the wooden subfloor and tile over the cement board and tubing without the aluminum plates to save $$$. My thoughts on the thermal mass were that once the cement board reached temperature, it would distribute the heat more evenly as well as take less energy to remain at the temperature. With wood prices going wacko, I'm trying to save but have an efficient system at the same time.
Tiling over PEX radiant heat needs a layer over the PEX, an isolation member, then tile.
If labor is free (DIY), the low cost solution is to staple down the PEX, dry pack a mortar bed, isolation member, then tile. This will have the most thermal mass, and weight. Check the floor stiffness.
If you are limited in changes to the floor height, then OSB sleepers, 3/4 OSB over everything, isolation member and tile.
Thermal mass does not affect energy required to heat a room over the long term. Just introduces hysteresis to heat input / room temperature change.
Floor height as well as floor stiffness are both issues. Stiffness was another reason for the cement board; but obviously that's not the way to go. You gave me some good information. Thank You.
The best product that I know to install a radiant floor on top of an existing subfloor is the Roth Panels System see following link : http://www.roth-america.com/PDF_Download_Files/RothPanel_SellSheet_1.pdf . I have used it several time, being made of EPS insulating foam on bottom with a full face aluminum sheet bonded on top with grooves every 6'' to snap in the pipe, so it's quite easy to handle and install, come in sheet of 2' X 4'. You can install any type of floor finish on top. With hardwood, don't forget to use a thermostat with a floor sensor to limit the floor temperature if you don't wanted to overdraw the hardwood. If you are looking for design, Roth can offer you help designing your system, they did supply me with a panels and pipe layout in the past, they are very helpful.http://www.roth-america.com/PDF_Download_Files/Roth_DesignServices_BR_5.2019.pdf . Good luck.
Thanks for the reference and the link. What did you do for a heat source? How about the controls/pumps/valves? Did you install yourself? I am finding my 500sq/ft project is not big enough to have a plumber call me back! Kurt
The heat source will depend on the size of the project. My project I did was for a master bathroom of about 150 sq/ft. the rest of the house was heated with a force air system, and I've use a small electric water heater of about 3 USG, that work on 120V. For a 500 sq/ft project you will probably need a larger one depending on your heat load. As for pump/control for that small project I've use what is call a Mini Mixing Station from Roth also, see attach spec sheet. You can hook up two loops on it with a two loop adapter they have, depending on the pipe size you can do up to 540 sq/ft. work on 120V and come with a Room Temp Sensor with a capillary which doesn't need power. I had everything installed in the bottom of a bathroom cabinet. Depending on your level of knowledge with radiant heat I would really suggest that you get in touch with a tradesperson, your first step would be to know what king of heat load you have.
I have a 1200 sq ft home with a 3 zone radiant heat system. I am using a 6.6 gallon condensing tankless water heater as my heat source. It is 160K BTU at max heat. I have it set at 120* output. The input water reaches 100* after running awhile. so the net temp gain is only 20* but it can start as low 60*.
It is a staple up system running a double run of 3/8" PEX tubing with no plates. And minimal insulation. Partially because we are also heating the basement with the same tubing. We do plan on finishing the basement and putting in some type of radiant flooring system. Warmboard or similar. And putting down cork underlayment as a thermal break. We have no problem with water intrusion as we live in a mostly arid high desert in Colorado. We have a sand/rock base below our basement floor, but no insulation.
When we do the basement finishing, we plan on putting Rockwool insulation in for both sound control and heat control.
In the attached pictures, the old tankless water heater is shown. It was a 199K BTU unit that failed after 15 years. The system was designed by the prior owner who allegedly was a licensed plumber. The system is a puller and not a pusher. The central pump does push the water towards the distribution panel (The circ panels picture) The circulation pumps PULL the water through the pipes. I have always thought this to be a strange way of doing things.
There are two zones open, those are the ones I am planning on using for the basement. zones.
That’s a great delta T. Sounds like a great project you have ahead of you! We are going on top of the subfloor.