DIY radiant floor installation

I would personally not consider building a house on a polished slab on grade in a cold climate without heated floors. Heat moves from warm to cold, your body is 37C, and concrete is highly conductive. all those variables mean your floor will suck the heat right from your feet. The sensation is less pronounced with less conductive flooring materials such as wood, but concrete will always feel colder. It is well explained here – 

How to design a home for thermal comfort

And I tell you the above from a personal experience with our last demo house which was the first LEED V4 in Canada and it also met Passive House performance requirements even though it we didn’t seek certification.  We used the house as a teaching venue and one day when I had a class and the floor heat was not activated, but the air temperature was warm. People were asking if they could put their shoes on since their feet were cold, despite 8 inches of insulation below and even a 3/8” surface covering of cork. 

I know slab on grade Passive Houses often don’t include floor heat, but you wouldn’t catch me building one. At the very least you could consider making it ‘radiant ready’ and running some pex tubes in case for the future. The problem with hydronic heating and the reason it overshoots the temperature is because there is so much latent heat in water that when it shuts off it will still continue to heat the concrete for a while.

As an alternative I would suggest you look at a Legalett slab on grade with air heated floors. There is not as much heat in air so it doesn’t over shoot as much, and the entire system is embedded in the floor so there would be no ‘boiler room effect’ of overheating at the manifold in your mechanical room.  

Concrete is highly conductive, and even in a home kept at a typical room temperature it will still suck the heat right from your feet. 

Installing radiant heat in a concrete slab on grade floor will for sure make your home more comfortable. You do have a few options to make a slab more comfortable without a radiant heat, but were you planning to install a floor covering? A lot of variables will start to come into play, I’ll explain–

A polished concrete floor is the cheapest, most durable floor you can build, but concrete conducts heat easily, so it will suck warmth right from your feet. A way to make it more comfortable, would be to lay down engineered hardwood, Marmoleum, cork, or some other floor covering. But that addition could easily cost you more than a heating system, so it depends on what your desired finished floor is.

We built a slab on grade with 8 inches of sub-slab insulation, and even with that much it was still a bit cool on the feet. So personally, I am all in for warm floors. Life is too short (or perhaps too long) to spend it with cold feet. See this page to learn more –

Choosing the best heating system - How to design a home for thermal comfort

So here are some questions and we can help a bit more probably – where are you building, how much insulation are you laying down, and are you installing a floor covering?

As for Legalett, Neither air heated radiant floors or hydronic stands out as clearly cheaper to install or operate than the other, the advantages to an air heated floor is a more even distribution of heat, less risk of damaging the system during construction (no chance of water leaks), and less equipment in the mechanical room which mitigates them becoming the hotspot. The other interesting possibility with the Legalett system is that it can be either gas or electrically-heated using a coil in the heat distribution box.