Pex layout spacing/simple design guide for radiant?
I am trying to determine pex spacing for shop area and house area for my monolithic slab.
I am in zone 4a and building a 28×80 house/shop (1120 sq ft each) and was gifted a BUNCH of 3/4″ pex yesterday from a friend who had it left over from his ICF house and shop.
So I am going to plumb the concrete floor for radiant since the price is right 🙂
The house and shop will have pretty good air sealing and insulation as well as tall ceilings (10ft house/12ft shop). I will have 3″ of recycled 25psi XPS under the slab and edge beam/footer (monolithic slab). Air sealing will be in the 1.0 ach area for house, and as tight as feasible with a giant garage door in shop 🙂
The shop is where I will spend most of my time as I am planning a small scale manufacturing business for my family.
Thank you for your advice or a reference link.
-Mike
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Replies
https://assets.supply.com/ul_pdfs/712617_ownersmanual.pdf
3/4 is not the easiest to keep down, so be carful with the layout you pick so that there are no tight spaces where it will kink.
Most well insulated houses need only about 1/2 to 1/3 of the floor area heated, too large of an area heated and it will never get hot enough to be noticable.
Best to only heat areas with high traffic (hallways, entrance mudroom, kitchen, bathroom) and areas near the perimiter with larger openings (doors, windows). The rest where you'll most likely have furniture and areas you'll never walk over don't need any heat.
I prefer to staple the pex to foam, but I think 3/4" won't stay put that way. Make sure your free pipe doesn't become a nuisance and float on you when you pour the concrete.
Zones cost money (vales, manifold, thermostat) adds up quickly. Pick zones that make sense and as few as possible. For example, I usually have bathrooms as a dumb zone. If any zone is calling for heat, the bathroom will also get heat.
Akos, thanks for answer; but, I am a bit confused at: "Most well insulated houses need only about 1/2 to 1/3 of the floor area heated, too large of an area heated and it will never get hot enough to be noticable."
How will heating more of an area not get hot enough? Am I misinterpreting what you are saying?
Thanks for the clarification.
-Mike
Mike,
It is about surface temperature.
If you heat the full surface area in a low load home, the highest temperature you'll see might be 4F to 6F above room temperature. At those temperatures, the floor doesn't feel warm, just not cold.
By heating less of the surface area, you can now increase the surface temperature but get the same BTU out as above, resulting in a warmer floor. Hard surfaces need to be around 28C(83F) before they feel warm to the feet.
Here is some info of best temperature based on floor cover:
https://www.healthyheating.com/Thermal_Comfort_Working_Copy/Definitions/floor_temps.htm
If you have your building load, pick the temperature from the chart above then look at the heat flux at that temp to figure out how many sqft you need to heat.
You can always add more, but it just costs you more pipe, more plumbing parts and more pumping power.