Thinnest layer of overpour over rigid foam and product recommendations

rossn · February 2022

In your experience, what is the thinnest layer of a self-leveling concrete-type overpour that you could practically do over a layer of rigid foam. The foam can be 60psi. Also interested in overpour product recommendations.

I have an uninsulated basement slab and am needing to get my floor assembly to at least R3 to manage my heating loss in my design. I also need to keep the assembly as thin as possible to manage ceiling height and stair code issues. Radiant heat will be present, but on the ceiling, not the floor.

Thanks!

Edit to add: There is a 4" below-grade slab that this assembly will sit on.

Alan (California Radiant) Forbes · February 2022

I've heard Hot Rod recommend three times the aggregate size. Using pea gravel, you can get down to 1-1/4".

"Beef up the mix with some plasticizers, fiber, etc."

Paul Pollets · February 2022

If this is a finished floor, the recommendation is 2" of lightweight concrete. Thinner pours will have more cracking.

Jamie Hall · February 2022

I'd go 2 inches -- and I would require fiber reinforced. It will still crack, but they will be microcracks and not noticeable. 60 psi foam will help a lot, but still be very careful about heavy point loads. Like pianos, for instance...

rossn · February 2022

Thanks for the comments... just to clarify, there is a 4" slab, but it is insulated. @Paul Pollets and @Jamie Hall, just confirming you are saying 2" over slab + 60psi rigid foam? Just making sure I'm understanding. If that is the case, I'll need to go back to sheet materials idea (likely MgO board), as I need to keep the full assembly 1.25-1.5".

The funny thing is that we see products like roth board and DriCore Insul-armor which are strictly foam panel, and they talk about finished floor right over that (which I cringe at). Now roth, appears to be 90psi foam, which is pretty good... but nothing like plywood or MgO.

hot_rod · February 2022

The gypsum based products can be poured down to a feather edge. With those you just need enough to cover the tube. Gyp may shrink a bit and it does need a sealer, depending on the final floor covering

with a 3/8 tube and a gyp product you might get down to a 1” pour, maybe thinner, check with the gyp manufacturers

small areas can be hand mixed, or get a gyp company to pump it in

The concrete mix you get at the lumber yard is usually a small aggregate so 1-1/4” over the tube

rossn · February 2022

Thanks, @hot_rod ! I had heard it could be thinner and was actually going to call the gyp-crete rep today and pick their brain, but somehow didn't happen. In this case, there won't be any radiant in the floor... rather, warmboard on the ceiling - so maybe there is even a chance to get under 1"... esp, if I could locate 90 psi foam.

I feel like the gyp over foam is an assembly I wouldn't have to worry about removing, should there be a pipe break or other flood event below-grade. I would just have to figure out how to get the bottom plates dried out. I had been looking at a dimple matt topped with foam, then 2 layers thin MGO, but the issue I have there is that the dimple mat has dimples that would hold water in any water event, and I think that would require tear-out to some degree.

We're talking about 1500sf, with some areas actually needing leveling so I'd probably look for a gyp company to do this.

Below grade - would be going LVT.

Jamie Hall · February 2022

To make mycomment a little clearer -- if you have flooring over the concrete which has any strength -- engineered hardwood, regular wood flooring, anything like that -- you won't have a problem.

rossn · February 2022

For posterity, I found a pretty interesting article in StructureMag that has references to various (gypsum, cementous) leveling products, thicknesses, EPS beneath leveling agents... I'll still reach out to some reps to see what they think is possible.

PC7060 · February 2022

So the slab is insulated already, correct? If you’re really just looking for a thermal break between the finished floor in the concrete I don’t see any reason you want to put concrete or gyp over the insulated panel. Why not use a 3/4 inch layer of foam with sub floor mechanically attached through the foam into slab?
Alternately you could do use polyurethane adhesive (foam in the can type) to adhere foam to slab and use a floating subfloor system over that.

rossn · February 2022

PC7060 said:
So the slab is insulated already, correct? If you’re really just looking for a thermal break between the finished floor in the concrete I don’t see any reason you want to put concrete or gyp over the insulated panel. Why not use a 3/4 inch layer of foam with sub floor mechanically attached through the foam into slab?
Alternately you could do use polyurethane adhesive (foam in the can type) to adhere foam to slab and use a floating subfloor system over that.

Hello. The slab is not insulated today. I need a combined floor R-value of at least 3 to support my (ceiling) radiant design.

There are a few challenges: It is below grade, and I do want the assembly to be water tolerant... spills, leaks, washer hoses bursting, etc - all that stuff practically happens, and I would like to not have to remove the entire subfloor assembly if the inevitable does happen. Framing is already in-place, and there are some unique challenges such as the 50 year old slab is at 99% RH regularly, but there is never any bulk water or condensation (arid here). Internal framing is already in-place, which gives a few additional challenges related to the water tolerant assembly. The slab is pretty flat, but not perfect. There is one area (formerly garage), where the slab slopes down 1.5" and back-up on the other edge of the area... for that reason, going to a self-leveling pour would make it a 1-step process, versus a 2-step process.

The mechanical assembly I would consider is using MgO board over EPS foam, though thickness also has to be considered, given stairs, etc.

PC7060 · February 2022

rossn said:

Hello. The slab is not insulated today. I need a combined floor R-value of at least 3 to support my (ceiling) radiant design. There are a few challenges: It is below grade, and I do want the assembly to be water tolerant... spills, leaks, washer hoses bursting, etc - all that stuff practically happens, and I would like to not have to remove the entire subfloor assembly if the inevitable does happen. Framing is already in-place, and there are some unique challenges such as the 50 year old slab is at 99% RH regularly, but there is never any bulk water or condensation (arid here). Internal framing is already in-place, which gives a few additional challenges related to the water tolerant assembly. The slab is pretty flat, but not perfect. There is one area (formerly garage), where the slab slopes down 1.5" and back-up on the other edge of the area... for that reason, going to a self-leveling pour would make it a 1-step process, versus a 2-step process. The mechanical assembly I would consider is using MgO board over EPS foam, though thickness also has to be considered, given stairs, etc.

@rossn - understand, I had concerns about the moisture issues too; sound like you’ve got it covered.

Good luck!

TAG · February 2022

I'm all for planning -- but -- what is the finished floor going to be?

Have used warm board in an old basement and over new slabs ... I'm not in a flood zone and there is no moisture issues

rossn · February 2022

TAG said:
I'm all for planning -- but -- what is the finished floor going to be?

Have used warm board in an old basement and over new slabs ... I'm not in a flood zone and there is no moisture issues

Finished floor will be Vinyl Plank. Given it is below grade, I want a fully water tolerant assembly. The warmboard will be on the ceiling, in this case.

Alan (California Radiant) Forbes · February 2022

Here's a previous discussion a few weeks ago:

https://forum.heatinghelp.com/discussion/comment/1685930#Comment_1685930

Derheatmeister · February 2022

rossn said:

TAG said:
I'm all for planning -- but -- what is the finished floor going to be?

Have used warm board in an old basement and over new slabs ... I'm not in a flood zone and there is no moisture issues
Finished floor will be Vinyl Plank. Given it is below grade, I want a fully water tolerant assembly. The warmboard will be on the ceiling, in this case.

A couple years ago at the ISH Germany i saw a Cementatius 1/2" thick equation of the Viega Climate panel..This product is made by a Greek manufacturer which name i forgot..
This year at the AHR this manufaturer was displaying the Cementatius Panel near our Booth C 6636..If you are interested in this product as an option i can look at the AHR floorplan and find the Manufacturer..
Let me know.

rossn · February 2022

I could us a sanity check here:

With a 1" layer of gypsum (spoke to the Gyp-Crete rep) over foam, I should still be OK from a heat loss and comfort perspective?

I am envisioning the 3/4" EPS (R3.5) foam as a continuous thermal break, and that while it may take longer for the gypsum floor to warm up based on thermal mass (relative to a plywood subfloor), that it wouldn't be more lossy than another assembly, per-se. And, that the floor won't be cold, once thermally stable.

Do you all agree?

To me, it's the same concept as flooring on insulated slab.

rossn · February 2022

Alan (California Radiant) Forbes said:
Here's a previous discussion a few weeks ago:

https://forum.heatinghelp.com/discussion/comment/1685930#Comment_1685930

Alan, looks like that is a controls thread. Maybe you had a different one in mind?

rossn · February 2022

Derheatmeister said:

rossn said:

TAG said:
I'm all for planning -- but -- what is the finished floor going to be?

Have used warm board in an old basement and over new slabs ... I'm not in a flood zone and there is no moisture issues
Finished floor will be Vinyl Plank. Given it is below grade, I want a fully water tolerant assembly. The warmboard will be on the ceiling, in this case.
A couple years ago at the ISH Germany i saw a Cementatius 1/2" thick equation of the Viega Climate panel..This product is made by a Greek manufacturer which name i forgot..
This year at the AHR this manufaturer was displaying the Cementatius Panel near our Booth C 6636..If you are interested in this product as an option i can look at the AHR floorplan and find the Manufacturer..
Let me know.

Just making sure I'm following... this was a cement product with grooves for tubing?

Derheatmeister · February 2022

rossn said:

Derheatmeister said:

rossn said:

TAG said:
I'm all for planning -- but -- what is the finished floor going to be?

Have used warm board in an old basement and over new slabs ... I'm not in a flood zone and there is no moisture issues
Finished floor will be Vinyl Plank. Given it is below grade, I want a fully water tolerant assembly. The warmboard will be on the ceiling, in this case.
A couple years ago at the ISH Germany i saw a Cementatius 1/2" thick equation of the Viega Climate panel..This product is made by a Greek manufacturer which name i forgot..
This year at the AHR this manufaturer was displaying the Cementatius Panel near our Booth C 6636..If you are interested in this product as an option i can look at the AHR floorplan and find the Manufacturer..
Let me know.
Just making sure I'm following... this was a cement product with grooves for tubing?

Yes the product is Called interplast and they are now somewhere on the East coast : https://www.interplast.gr/en/proionta/endodapedia-xiras-domisis/pleonektimata
I will get contact information when i get a second..

Update: This is the information i pulled from the AHR exhibitor list: The booth Number was C6740 the contract is Dimitrios Tzavelas
Sales Manager
+30 6974060005

hot_rod · February 2022

rossn said:
I could us a sanity check here:

With a 1" layer of gypsum (spoke to the Gyp-Crete rep) over foam, I should still be OK from a heat loss and comfort perspective?

I am envisioning the 3/4" EPS (R3.5) foam as a continuous thermal break, and that while it may take longer for the gypsum floor to warm up based on thermal mass (relative to a plywood subfloor), that it wouldn't be more lossy than another assembly, per-se. And, that the floor won't be cold, once thermally stable.

Do you all agree?

To me, it's the same concept as flooring on insulated slab.

The pour gyp products really don't like to get wet. It comes apart like wet sheetrock. You can seal the top for some spills, but if it gets wet from the side of bottom it will become mush. That was a concern in your top post.

The Roth Panels in 3/8" tube size are 1/2" thick, plus your floor covering. Get a 5/16" thick hardwood, gets you a 13/16" thick build up.

Derheatmeister · February 2022

hot_rod said:

rossn said:
I could us a sanity check here:

With a 1" layer of gypsum (spoke to the Gyp-Crete rep) over foam, I should still be OK from a heat loss and comfort perspective?

I am envisioning the 3/4" EPS (R3.5) foam as a continuous thermal break, and that while it may take longer for the gypsum floor to warm up based on thermal mass (relative to a plywood subfloor), that it wouldn't be more lossy than another assembly, per-se. And, that the floor won't be cold, once thermally stable.

Do you all agree?

To me, it's the same concept as flooring on insulated slab.
The pour gyp products really don't like to get wet. It comes apart like wet sheetrock. You can seal the top for some spills, but if it gets wet from the side of bottom it will become mush. That was a concern in your top post.

The Roth Panels in 3/8" tube size are 1/2" thick, plus your floor covering. Get a 5/16" thick hardwood, gets you a 13/16" thick build up.

FYI ..After talking to Dimitrios Tzavelas this Morning he insured me that this Product would not become Mush if it is Subjected to Moisture ,Spills or Condensation..
It is a very dense heavy product and has a proven track record..

TAG · February 2022

With the OP wishing to use foam and some type of overpour on the floor and then place vinyl planks on top ... why not just lay in 3/8 pex on top of the foam and do the pour and be done with it. I can't fathom fighting with Warmboard on a ceiling -- or any other like type product. With it on the ceiling my guess there will be a need for higher temp water as well. Heat in the floor is better and if it ever got wet the Pex will not care

I'm also interested in the OPs location .... did a project in NJ and even in very cold temps the basement floor never really got that cold 6' in the ground. You want a thermal separation with the old slab -- my 1500sf basement does not have a huge heat load. I'm glad I did a lot of shorter loops as it's allowed me to basically shut some off -- it would overheat if I sent the same temp water through them like the first floor

Alan (California Radiant) Forbes · February 2022

Alan, looks like that is a controls thread. Maybe you had a different one in mind?

I was wondering where that comment went. I posted it on a different thread.

rossn · February 2022

Thank you Derheatmeister. Unfortunately, that wouldn't be a good fit for me because 1) it's conductive and I need something insulate from the uninsulated slab 2) I'm not trying to put the heat on the floor... just create an insulated subfloor assembly.

rossn · February 2022

hot_rod said:

The pour gyp products really don't like to get wet. It comes apart like wet sheetrock. You can seal the top for some spills, but if it gets wet from the side of bottom it will become mush. That was a concern in your top post.

The Roth Panels in 3/8" tube size are 1/2" thick, plus your floor covering. Get a 5/16" thick hardwood, gets you a 13/16" thick build up.

hot_rod Thanks for that very useful information. Odd thing is the Gyp-Crete rep didn't mention that when we talked about how it would absorb bulk water. That really has me curious, and I am going to call him back, because what you mention would direct us away from that as an option. The architect and I were actually leaning towards it. Bummer!

Ok, so let me answer the multiple questions about tubing on the ceiling, which will be both upstairs and downstairs.

I had a radiant professional who had lived with ceiling radiant suggest the idea.

Upstairs: It's an older home, though a fair bit rebuilt. Lots of glass. Putting heat on top of the subfloor would require about 32 BTUs/sf. However, floors are not being replaced at this time, and there will be some major future kitchen changes with island, etc. Beneath isn't a practical option... the framing is not clean, to say the least. Some areas even have LVL construction adhesived to the bottom of the subfloor, as blocking. I did one section of radiant engineering heat plate beneath the bathroom, and it was excruciating to say the least. Unfortunately, there is no wall space for radiators or baseboard. Forced air isn't a remote option post remodel.

Downstairs: Uninsulated slab, 4' below grade. We live in a zone that has more heating than cooling during the year. I've had water events (significant plumbing leaks, black water backups, and water infiltration due to flooding) in prior homes. I really want to create a subfloor assembly that isn't going to have me ripping it out at the next flood event, which meant not putting Warmboard on the floor. At the time of the decision (some time back), I wasn't leaning towards the build up of the insulated subfloor, but putting carpet back down. That said, we re-evaluated and decided we really did not want carpet, yet I still need a R3 on the floor for my design.

Now the warmboard for downstairs is already purchased, but not installed, and I will be having a lot of warmboard-R upstairs on the ceiling, as well. That is about to get purchased before prices jump again.

Aside from the water concerns, what about putting the heat on the floor? Now that we are rebuilding the stairs, there is a bit less of a concern about downstairs subfloor thickness, though we should still keep to about 2" for the full floor with 3/8" vinyl plank. With recent information, there could be a case for going up to 2-3/4" (and doors would be cut short), but that was not the case originally.

I keep hearing about Roth, and see 4 practical concerns with it.
1) Need about 28 BTUs/SF and you all can advise me, but think that is pushing it (esp. given some areas will have significant area covered with area rugs, such as the theater area)
2) I have trouble thinking it is appropriate to put directly over cold slab... the heat loss to the slab would be significant with barely any insulation behind the tubing. I think Roth advises against additional foam beneath their insulation
3) It is hard to believe their foam is sturdy enough to put flooring directly over without long term issues... my architect did not like that idea at all. I think 3/4" plywood is in the multi-thousand PSI range, whereas roth is 90psi or something similar. Not to mention... I think they leave areas of foam exposed... that is to code with 1/2"+ wood surface over it, but not if I put down vinyl plank.
4) I would still have leveling issues with it. Most of the slab is actually pretty good, but the transition into the former garage and floor drain slope would easily be overcome with a self-leveling pour.

All of that combined is why we landed on ceiling, but always glad to hear thoughts or alternatives. FWIW, the overall system (I also have radiators in the master, heat plates under the master bath, fan convectors in a heated shop, and myson linear radiators in a studio) was designed around 130 AWT at design condition.

The boiler is a monster cast iron that we setup a two-temp system on outdoor reset. Now that we pulled the trigger on the upstairs remodel, the second (180) temp isn't needed anymore, though the vision was to eventually get everything to 1 temp and a high efficiency boiler in the long run.

Thank you all for the ideas.

rossn · February 2022

TAG said:
With the OP wishing to use foam and some type of overpour on the floor and then place vinyl planks on top ... why not just lay in 3/8 pex on top of the foam and do the pour and be done with it. I can't fathom fighting with Warmboard on a ceiling -- or any other like type product. With it on the ceiling my guess there will be a need for higher temp water as well. Heat in the floor is better and if it ever got wet the Pex will not care

I'm also interested in the OPs location .... did a project in NJ and even in very cold temps the basement floor never really got that cold 6' in the ground. You want a thermal separation with the old slab -- my 1500sf basement does not have a huge heat load. I'm glad I did a lot of shorter loops as it's allowed me to basically shut some off -- it would overheat if I sent the same temp water through them like the first floor

Hi TAG - a bit of background on 'why ceiling?' is included in my response to Hot Rod. Given all the changes that are now going in place, maybe I do need to reconsider before I pull the trigger on warmboard for upstairs. That said, the distribution system with manifolds are already in-place for the warmboard. With the warmboard on the ceiling, I can actually go to higher temps than floor and get more BTUs/sf out of it.

What is the thinnest I could go with the pour over tubing and foam? Is that done with concrete? 1" foam? Sure would be nice to not have to insulate the mid-floor.

My slab is currently around 55 degrees in the construction zone, and that is what I've always considered our ground temps here near Denver.

Agreed that the warmboard will be a PITA to install. Leveling the upstairs ceiling framing was tedious (since you can't have shims between the warmboard and drywall).

TAG · February 2022

We had a house at the beach with electric radiant in the ceiling plaster when I was a kid ... I'm not really sure why this was a "thing" .... one of my neighbors said it was because if it flooded (we were on the ocean). I never bought this theory even with all the electric wired up into the attic and not down -- IMO it was more likely just a builder who worked with it and sold it as a better way vs electric baseboard (one did have to be careful with the electric baseboard). It did work and most people used the houses seasonally -- but, it was a bit strange feeling. Not necessarily in a bad way ... but -- not really great either. Over the years I have added spots of wall and ceiling hydronic into my projects when I was forced to ... but it was always because I had to.

We all have to make our own decisions ..... are you sure you need 32 BTU's sf?

I totally get the problems of the plates in some situations -- just too many things in the way. Also -- getting above 25 BTU's Sf is a problem if my memory is correct. Two years ago I took advise here and we did a 1k sf living room retrofit using the heavy plates and 3/8 tubing and it has worked very well. I had never done the plates with 3/8 before .... wet beds with tile and 3/8 with great results. 3/8 tubing using about 160' loops has worked flawlessly. It's easy to work with

I would really think hard about warmbord on the ceiling for the lower level w/ slab --- you do want a thermal separation with the old slab. But the delta there is only going to be 25 or so -- it's not like you need the same R as if it's up against a 5 degree wall in the winter -- or slab on grade. I remember doing a shower and even using the 1" behind the wet-bed the back side was not warm at all.

You can also get a bit more heat in the lower level with it on the floor and I have always found this to be both comfortable and that extra heat help the floor above

hot_rod · February 2022

32 btu/sq ft is getting to be a pretty big load for radiant floors. Radiant ceilings and walls as others have indicated can have a higher output, with higher surface temperatures possible.

Walls have a slight advantage over ceilings as temperature will stratify at the ceiling systems, increase ambient at the surface and drive down the delta a bit.

Here are the two multipliers, and math to use for both ceiling and wall outputs, from Caleffi idronics #6.
Using 110°F as SWT and 70° as ambient the walls would give you about 32 btu/sq.ft, the ceilings 28.4 btu/sq. ft.

But now you need to assure you have enough wall or ceiling square footage to cover the heat load

rossn · February 2022

TAG said:

We all have to make our own decisions ..... are you sure you need 32 BTU's sf?

Thanks for the thoughts, TAG. Really appreciate it, and agree that this requires some serious thought, now that the stairs issue will not be a code issue with a little thicker floor.

On my project, I used the Uponor ADS suite to determine my heat loss. It is pretty detailed; as an example it includes things like 'slab below grade', and asks how much of the room is below grade. There could be a parameter off that I'm not spotting, but have reviewed several times. What i will say is that the master and master bath are done (3 radiators, 1 HO baseboard in the closet, heating plates under the master bath tile (not insulated below, yet), and a towel warmer. That area had no problem keeping up when we were a few degrees below design condition, though the system might have been running 5 degrees above what we were supposed to be targeting.

I would also note that I haven't run the analysis for 'what if the heat was on the floor', and that probably makes sense at this point.

Practically speaking, what pours over radiant tubing are commonly used (besides gypsum) that don't require a ton of work to prep the surface before a floor? I'm assuming there are some cementous products, though have heard they are much more than gypsum. One flooring guy mentioned Shonox to my wife yesterday, but maybe that was a leveling-only agent.

Edited, as it has been a while since I've been in ADS, and it does actually ask how far below grade the room is.

rossn · February 2022

hot_rod said:
32 btu/sq ft is getting to be a pretty big load for radiant floors. Radiant ceilings and walls as others have indicated can have a higher output, with higher surface temperatures possible.

Walls have a slight advantage over ceilings as temperature will stratify at the ceiling systems, increase ambient at the surface and drive down the delta a bit.

Here are the two multipliers, and math to use for both ceiling and wall outputs, from Caleffi idronics #6.
Using 110°F as SWT and 70° as ambient the walls would give you about 32 btu/sq.ft, the ceilings 28.4 btu/sq. ft.

But now you need to assure you have enough wall or ceiling square footage to cover the heat load

Thanks, Hot-Rod.

To your point, the math is a bit different on the ceiling, and I am confident in the current design using warmboard specific ceiling charts and the Uponor ADS software having the heat source configured as coming from the ceiling. We are assuming 41 BTU/sf warmboard @130 AWT.

I will re-run the analysis using the floor as the heat source with r4.6 insulation layer over slab and see what it says. The good thing is flooring will be vinyl plank, which seems to have almost no R-value.

I think my biggest problems at this point would be the fact my distribution system is already installed, and is based at peak AWT=130. Maybe there is a way to use some sort of mixing valve at the manifold in order to drop that for an add-on manifold. Note that the current design is using wall TRV controls.

rossn · February 2022

Ok, I re-ran the upon analysis, but there are a few variables that could significantly affect the heat loss/demand.

When I look at the heat loss on a room-by-room basis for the rooms considered and am now assuming 1" slab insulation. I am coming back at 25-26 BTUs/sf, assuming the below settings.

1) I wasn't sure what to use for floor covering R-value to compensate for area rugs; I guessed R1.25 combined. I think Vinyl Plank is extremely low... like R=0.05. I assume we will have area rugs, but not everywhere, and if appropriate, they don't have to be super thick. What overall flooring R-value do you use to compensate for area rugs that might cover 1/3 of the room?

2) Uponor ADS isn't really configured to measure for insulation on top of the slab, and there isn't a good manual for the software. Based on the below, do you think 'Permitter R-value' and 'Edge R-Value' pertain to the slab? I'm not sure what the difference would be. If so, since my insulation is on-top of the slab, I would think they would actually be very high... call it 20. Do you all agree? If so, my BTUs drop to below 23.

TAG · February 2022

Basements don't leak (air) .. that's a big factor. My place in central NJ has a full size basement -- my office area is 18 x 36' and I have two single depth panel radiators -- they may be 2x3' ... I think at max temp they do 9000btu's. The boiler never goes over 140 degrees (not full temp of 180) ... even at full output that's 12 Btu per sf. The floors are tile .... no insulation in the slab (50's construction)

You want the thermal separation over the old slab when doing radiant so you are not heating the slab and the heat is going up --- I did a Warmboard over a slab in this same house back in the early 00's when the product was very new. Single story addition bump out --- slab on grade construction. Ploy VB on top of slab -- 2x material ringing the room perimeter on the flat. Filled in the center with more 2x on the flat at 16" on center. 1.5 foam cut between the 2x material. Warmboard and strip white oak .... the room is all windows on two sides and the Warmboard has no problems.

I think you may want to spend a couple $100 and get a good heat load done so you are not spending more than necessary. Also -- even one panel can add a lot if you can stick it some place. I have used the double thick ones 18" wide by 3' high ... they throw out a lot of heat

ScottSecor · February 2022

I'm with @TAG on this. Here in NJ most basements in homes only need minimal heat. I'm guessing here, but the "average" 1000 square foot basement might require say 6000 btu on design day. Larger home with 1800 square foot basement might require 10,000 btu. Unless home is on a hill and has lots of windows/sliders I think you might be overdoing it.

hot_rod · February 2022

rossn said:
Ok, I re-ran the upon analysis, but there are a few variables that could significantly affect the heat loss/demand.

When I look at the heat loss on a room-by-room basis for the rooms considered and am now assuming 1" slab insulation. I am coming back at 25-26 BTUs/sf, assuming the below settings.

1) I wasn't sure what to use for floor covering R-value to compensate for area rugs; I guessed R1.25 combined. I think Vinyl Plank is extremely low... like R=0.05. I assume we will have area rugs, but not everywhere, and if appropriate, they don't have to be super thick. What overall flooring R-value do you use to compensate for area rugs that might cover 1/3 of the room?

2) Uponor ADS isn't really configured to measure for insulation on top of the slab, and there isn't a good manual for the software. Based on the below, do you think 'Permitter R-value' and 'Edge R-Value' pertain to the slab? I'm not sure what the difference would be. If so, since my insulation is on-top of the slab, I would think they would actually be very high... call it 20. Do you all agree? If so, my BTUs drop to below 23.

Does the program know you have heated space above? I'd expect a basement to have a load of 1/2 that number

rossn · February 2022

TAG said:
Basements don't leak (air) .. that's a big factor. My place in central NJ has a full size basement -- my office area is 18 x 36' and I have two single depth panel radiators -- they may be 2x3' ... I think at max temp they do 9000btu's. The boiler never goes over 140 degrees (not full temp of 180) ... even at full output that's 12 Btu per sf. The floors are tile .... no insulation in the slab (50's construction)

You want the thermal separation over the old slab when doing radiant so you are not heating the slab and the heat is going up --- I did a Warmboard over a slab in this same house back in the early 00's when the product was very new. Single story addition bump out --- slab on grade construction. Ploy VB on top of slab -- 2x material ringing the room perimeter on the flat. Filled in the center with more 2x on the flat at 16" on center. 1.5 foam cut between the 2x material. Warmboard and strip white oak .... the room is all windows on two sides and the Warmboard has no problems.

I think you may want to spend a couple $100 and get a good heat load done so you are not spending more than necessary. Also -- even one panel can add a lot if you can stick it some place. I have used the double thick ones 18" wide by 3' high ... they throw out a lot of heat

My 'Basement' might be a little different. On one end, it is less than 1/2 below grade, and the other end even less. So, I get all the drawbacks of having slab below grade plus air leakage

provided 25Btus is within reach on hydronic, I need to confirm I could not have peak 130AWT water running in the proposed overpour setup (I'm not sure if you can go higher temp on overpour, do to heat dissipation). Assuming I need a 2 temp setup, I need determine the feasibility of that with the existing distribution tubing already in-place, and with manifolds already installed.

If all those cards fall into place, then I agree confirming my numbers needs to happen. I did reach out to the radiant specialist that helped me setup the original two-temp system at the boiler.

Thanks again, TAG and all!

rossn · February 2022

ScottSecor said:
I'm with @TAG on this. Here in NJ most basements in homes only need minimal heat. I'm guessing here, but the "average" 1000 square foot basement might require say 6000 btu on design day. Larger home with 1800 square foot basement might require 10,000 btu. Unless home is on a hill and has lots of windows/sliders I think you might be overdoing it.

That is good context. I'm at 1,350sf (disregarding unheated areas such as storage rooms, utility room, beneath stairs) and about 28,500 BTUs. As per my reply to TAG, this level is maybe 60% exposed and 40% below grade, and uninsulated slab. There are a decent number of good sized slider windows. 2-3 per room that are big enough for egress.

Does that change your perspective notably?

rossn · February 2022

hot_rod said:

Does the program know you have heated space above? I'd expect a basement to have a load of 1/2 that number

I have 3 options and configured as 'heated from same source'. Toggling to 'heated from other source' doesn't change values, but if I set to 'not heated' it skyrockets.

Air changes are another significant factor, and I used 1.0/hr. Old 1960's contruction, but will be reasonably well sealed when done to the extent possible on an older home. I will also have two pairs of Lunos Spot HRVs in this area.

Is that a reasonable number to use for what I've described?

Here is a sample room... the one with the most windows... maybe you all will spot a mistake.

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ScottSecor · February 2022

@rossn this does change things. I missed that your basement was a "real" living space with lots of glass. I was picturing a typical basement with four or five windows that measure 12 inches by 30 inches that are so prevalent in my area. I also incorrectly assumed that your basement was a more typical eight foot ceiling with two feet or two and a half feet of exposed walls with the rest below ground.

I just did a very crude heat loss calculation for a 30x45 basement room with eight foot ceilings, 150 square feet of high quality windows, average exposed wall is 5.5feet above grade, no loss above, no insulation in the below grade slab, R-11 in basement walls and no ceiling insulation. I came up with 19,541BTU for 1 degree outside and 70 degrees inside.

Hope this helps.

rossn · February 2022

ScottSecor said:
@rossn this does change things. I missed that your basement was a "real" living space with lots of glass. I was picturing a typical basement with four or five windows that measure 12 inches by 30 inches that are so prevalent in my area. I also incorrectly assumed that your basement was a more typical eight foot ceiling with two feet or two and a half feet of exposed walls with the rest below ground.

I just did a very crude heat loss calculation for a 30x45 basement room with eight foot ceilings, 150 square feet of high quality windows, average exposed wall is 5.5feet above grade, no loss above, no insulation in the below grade slab, R-11 in basement walls and no ceiling insulation. I came up with 19,541BTU for 1 degree outside and 70 degrees inside.

Hope this helps.

ScottSecor - thanks so much... that was very generous of you to do!! You nailed it on the windows... I'm at 155sf. My layout is also a little longer and narrower, which doesn't help, and my insulation on average should be better. All this means there is additional room for review and confirmation before committing to the design - so thank you (and all) for bringing that to light!

Are 25 BTUs/sf practical out to get out of an overpour floor radiant system, assuming some insulation beneath? I have seen the charts for warmboard, but not familiar with overpour.

Thinnest layer of overpour over rigid foam and product recommendations

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