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Retrofit Hydronic Infloor heating to existing slab, polished concrete

lummock
lummock Member Posts: 3
edited October 2022 in Radiant Heating
I have a 100 year old home with cast iron radiators throughout, located in Northern Ontario Canada.
It is comfortable and reasonably easy to heat, despite temperatures being cold in the winter.

I am in the process gutting and refinishing the 70’s finished basement. 

Part of this process will involve moving from a mid efficiency boiler to a condensing combiboiler for space savings, and efficiency, I have read plenty of horror stories on combis, but I will persist as we don’t have the space for a tank. 

The prior owner had built cast iron radiators, on their own zone, INTO the 2x4 walls which were insulated with fibreglass bats. This was probably not ideal from a heat transmission perspective, and will not be part of the new plan.

I assume the slab is uninsulated.

I would like to add a heated polished concrete, or  gypcrete /epoxy, floor, roughly 1000 sq feet and remove all the cast iron radiators. 

How much headroom would i give up to achieve this? Currently the floor is just vinyl tiles glued directly to the concrete slab, and is cool underfoot summer and winter.

I have looked a lots of products such as warmboard,Roth panels etc, but Im still a bit unsure if any of them are a smart idea.

I have read about perimeter insulation and disconnecting the slab, but am unsure the value or how to achieve this.

The walls and rim joists will all be sprayfoamed. 

Though I will be jackhammering sections of the floor to move toilets I’m not keen on doing the whole floor in order to add 2” of rigid insulation and repouring my slab. I’m also not sure if this would damage the house.

I appreciate any suggestions as to if this is a non starter or if this can be done.

This is not a house I plan on flipping, it will done right or not at all.

If there are suggestions please include the rough finished height as well as the order of materials, it’s hard to picture how much headroom I’ll lose.

I could be convinced to move away from radiant floors, and polished concrete, but if so I would also like something to insulate the slab as the floor is cold as it stands.


thanks in advance

Comments

  • hot_rod
    hot_rod Member Posts: 18,211
    It will come down to how much heat energy you want to give up to the ground below 
    2” under slab insulation  is common these days, plus slab get you up into your headroom a bit. Stairs would need to be reworked 

    So those are the trade offs. Radiant ceiling s good second option
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 637
    I believe a product like Warmboard would have some insulation value to thermally uncouple from the slab below. It also has the aluminum surface on top to conduct heat to whatever finished floor material you'd use. The floor height it would add is the least you could practically expect to gain. But it does not come at a low price-point. Hot rod's radiant ceiling is a good alternative (the next best) to radiant floor. You MUST insulate above the radiant tubing.
  • lummock
    lummock Member Posts: 3
    Can you put fiber reinforced concrete or gypcrete over Roth panels or warm board? 
    If so what is the minimum recommended thickness? 

  • psb75
    psb75 Member Posts: 637
    I suppose you could. But...you'd better ask Warmboard tech support. They'll certainly have an opinion. I found them to be very helpful.
  • Zman
    Zman Member Posts: 7,434
    lummock said:

    Can you put fiber reinforced concrete or gypcrete over Roth panels or warm board? 

    If so what is the minimum recommended thickness? 

    If you are imbedding the tubes in concrete, you really don’t need warmboard.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • psb75
    psb75 Member Posts: 637
    Then, where does the thermal isolation from the old slab happen?
  • hot_rod
    hot_rod Member Posts: 18,211
    lummock said:
    Can you put fiber reinforced concrete or gypcrete over Roth panels or warm board? 
    If so what is the minimum recommended thickness? 

    I’m not sure concrete over aluminum is a good idea?

    If you use a pea gravel concrete mix3/8” aggregate you could get down to a thin pour. As I recall 3 times the stone size over the tube

    Expect “road map” type cracking on a thin slab. The fibers in the mix make it hard to get a mirror finish unless you power trowel
     which melts off the exposed fiber.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • lummock
    lummock Member Posts: 3
    psb75 said:
    Then, where does the thermal isolation from the old slab happen?
    Psb75 That’s the question I’m struggling with, how to isolate the slab as best as I can whilst still keeping build up low. 

    Obviously in an ideal world 2” eps and 4” concrete is the solution.

    Hotrod, can you elaborate on what you mean by a proper trowel, it sounds like something heated.

    I hadn’t thought of problem of aluminum over concrete would it flex or crack more easily 

    thanks again for you comments 


  • hot_rod
    hot_rod Member Posts: 18,211
    I think the lime in the concrete may attack the aluminum? Maybe once it cures it would be fine?
    Power trowels burn off those polypro fibers from the friction. And, properly operated< get you the most polished finish. Electric versions for indoors. On the large commercial slabs they have ride on versions.

    Rigid foamboard like Dow is the best for under concrete, it's rated for that use. My thought would be 1" minimum, R-5. Anything thinner tends to crack and break when you work with it. With the pre-made over the slab products, it's the thickness under the tube where the heat loss occurs and insulation is thinnest. I like the Roth panel, but maybe 1/4" of foam under the tube.
    I'd rather the tube on a solid 1". but it is the " tradeoff.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 637
    I thought Warmboard had a version with insulation underneath it. It doesn't. Roth panels do. Their 1/2" panel has R 4.5. That's the most they offer. Most of these radiant panel systems are designed for most flooring products: hardwood, tile etc. If you want something approaching the performance of concrete (i.e. more thermal mass) use Hardiboard and tile. Not quite the same mass as 4" concrete but more than wood.
  • hot_rod
    hot_rod Member Posts: 18,211
    I've alway been told about the best you can get from any foam is R-5 per inch. So I',m not sure how a 5/8" thick foam panel gets 4.5? Also below the tube is certainly not R-4.5? A bit of a sales spiel, unless the aluminum add r value :)

    I do like the Roth panel system, I have always used them over wood sub-flooring, glued and stapled down.

    I'd choose this over WB for over concrete and I like the 6" OC of the Roth better. The tight spacing and solid aluminum allows for the lowest SWT.

    WB is nice if you are nailing over it, it holds nails well.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream