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Community and Q&A

Retrofit Hydronic Radiant Heat in Basement – How to maximize efficiency (Poured Concrete or Sleeper System w Heat Transf Plat)

Crynos | Posted in Green Building Techniques on

Hello everyone,

First off – allow me to Thank You all for sharing your expertise with novices like myself who are trying to find the best way to be efficient with their hard earned dollars.

Backstory; I have a large home in Northern Ontario (Home to -15F winters) that is heated 100% with baseboards. We are now renovating and are installing a new heating system that will combine radiant hydronic heat in basement and main floor (via staple-up) and then an HVAC system to move the air around up top floor. Due to height and build limitations, moving to fully forced air system would not work well.

My question for you fine folks as is follows: What is the best way to get the most efficient radiant floor heat from my basement?

I have a poured slab basement with walk-out at back (at grade) that appears to only be moderately insulated (vapour barrier). I only have 7’10” of ceiling height and don’t want to lose too much of it, but want my system in the basement to be able to heat most of the house by sending the heat upwards.

I have been recommended one of two options;
a) Poured Concrete over loose-laid PEX

b) Pex inside Plywood sleeper system with aluminum heat transfer plates (

My concern with the poured concrete is that I will end up spending all my money heating my existing slab and not the home. Meanwhile, I am worried that the plywood sleeper system won’t be ‘solid’, will creek and move, etc.

In both cases, I want to lay some kind of insulation below the PEX pipes , but no matter how much I search, I have not been able to find the right material to lay down.

I have also sent out a few queries to companies like “Warmboard” and “Quicktrac” to see about their pre-made solutions and whether or not shipping is available in my area.

In brief – what I would like to know is:

1. Poured Concrete over top of my existing slab or sleeper style system?
2. What can I use to insulate as an underlay (below the sleeper / fresh pour of concrete) that would ensure I heat upwards and not downwards, without taking up too much vertical space?

Thank you, sincerely!

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  1. Expert Member
    Dana Dorsett | | #1

    Using a molded high density EPS designed to for 3/8" tubing such as Roth panels (see: ) is about as good as you're going to do without taking up much. The Roth panels themselves are ~R3.7 between the tubing and floor. If you can afford another inch of headroom installing 1" of Type-II EPS under the Roth would add another R4.2.

    Don't use sleepers- fasten the subfloor through the panel to the concrete with masonry screws (taking care that you don't put a screw through the PEX.

    You may want to consider installing a radiant ceiling and just the 1" EPS under the subfloor with headroom that tight.

  2. Crynos | | #2

    Love the full aluminum sheeting on those Roth Panels. Thank you for sharing, hopefully they ship to Canada.

    I will be putting piping in the ceiling to heat the floor above, so that should provide some radiant heat as well.

    Would those Type II EPS be strong enough to stand/install flooring on?


  3. Expert Member
    Dana Dorsett | | #3

    Type-II (1.5lbs per cubic foot nominal density) EPS is rated 15 psi, but that rating is sort of irrelevant when there is a Roth panel + subfloor on top of it to redistribute the weight. Type-II EPS used under 4" slabs, even airport runways, and is the most common material used for insulating concrete forms.

    It's not under a footing holding up the whole house, which would be a serious enough load to have to do the math. It'll be a very firm floor no matter what, since it's fully supported by concrete slab, and will not deform beyond it's elastic limits.

  4. Crynos | | #4

    Kindly appreciate the specificity!

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