Radiant Floor Heat Question

yomax4 · Jul 8, 2020

I did the same thing in my home. 1/2" pex in the basement floor. I use a mixing valve and a Ranco so the water can never get above 90 degrees before the Ranco shuts off the pump. Toasty warm. I did the same in my shop and heat it all with an outdoor wood boiler.

robstaples · Jul 8, 2020

I did my 2250 ft2 shop with 1/2” 300 ft loops. Narrower at the perimeter then center. Buried a small tube for temperature probe. Use a bigger conduit.. you can’t push thermocouples very far. Except for startup , the temp variation is very low in and out of floor piping. I have 100 tons of thermo mass in concrete, I just set and forget temperature. ~60 to 70 takes about 24 hours. I put 2” blue foam under everywhere. I put two zones, bath and water room and the rest. Shouldn’t have bothered with two Zones. I use high efficiency water heater( condensing 35 gal ) with heat exchanger and three pumps. Added glycol at first fill. Big mistake. Doesn’t age that well. Lowered heater transfer rate. Only needed if house or heat would be abandoned for a long time.

I measured and took photos of the floor with pex and tapes laid out so we could add room divides and not hit the pex . We used metal stud laid on the floor with short nails and then fit the wood wall studs to pressure the metal to the floor.

Some ideas.

Small pex pipe just delivers less heat per time and takes longer to come to limit. Once it’s there, It runs to make up for losses.
Hole in the center of the insulation would be great if the ground temperature was near your desired operating temp. If it’s below, you will just pump heat into the ground.

ovrszd · Jul 8, 2020

I agree. I can't logically make the no insulation theory work in my mind.

TnWV · Jul 8, 2020

I purchased part of the insulation yesterday, but no one has enough in one place, so will accumulate the rest by the weekend. Pex will be delivered tomorrow, again, no one local carries more than one or two 300’ foot spools in stock and the pricing locally is insane.

This weekend I will begin the installation and hopefully it goes well since concrete is scheduled for next Friday. I’ll be relieved when it’s done, moving all the gravel has been exhausting. Lumber shows up next Tuesday so it’s just about time to move on to the next step!

Thanks for all the advice! I’ll get to starting a build thread as soon as I can get in the house before 10pm!

AHNC · Jul 14, 2020

Is your basement all sub grade or are there many doors and windows. Your heat load will be less the more there is below ground. You say that the upstairs will be "conventional" hvac. You may consider other options. Given that you will have a boiler, I assume, for 2100 sq ft of slab, you could also go with a hydro air system using the boiler for hot water to fan coils. You could do zoning that way. You cooling system would be smaller condensing units to each of the air handlers. Also, with the performance today of mini-splits and the options I would go that way.

ultrarunner · Jul 14, 2020

Home I'm in now has radiant in slab for the walk to daylight basement shop and rumpus room...

It was only turned on once because simply not needed... Rumpus tracks around 66-68 year round...

I have thought the money would have been better spent on radiant under tile dinning, living, bath and hall...

TnWV · Jul 14, 2020

The ground is sloping all around the basement with about 40’ of the back being full daylight with a French door and a couple windows. There will be a 10’ deep porch over the daylight portion.

The radiant is just to make the basement comfortable in the winter without a separate furnace. I probably could have gotten by with a couple wall mount gas heaters, to be honest, but just like the idea of the radiant and figure I might as well give it a go since it cannot be added later.

We have a main natural gas pipeline crossing our property, and get near free gas, so heating with anything electric, like mini splits, is out. If I were doing an electric system, mini splits is likely the way I’d go, or maybe geothermal.

A nice efficient natural gas system should serve me well and cost very little to run, heat wise. I may still run radiant loops under the main floor bathrooms at some point to warm the floors, but that is down the road if I find it’s needed/wanted.

Finished running the 6th pex loop just before dark, will do the last one tomorrow morning before work and hook the manifold up tomorrow evening to test with air. May have to take Thursday off work to get everything finished up. Concrete, pumper, and a crew to pour/finish are scheduled for 6am Friday. Now just have to hope for no rain.

We are building the house our selves and only hiring out the things that we simply can’t do, or just wouldn’t be timely to do, like shingles, drywall, concrete, etc., but I’m hoping after Friday I will have time to start a build thread with pictures and all that. A big load of lumber arrived today and a second is scheduled for Friday afternoon, and will be everything to get me to the top of the walls ready for trusses, so won’t be a lot of rest going on here for a while.

ultrarunner · Jul 14, 2020

Having lived in Europe and spending time in the homes of friends I gained a real appreciation for radiant heated floors... never cold and bathroom space always cozy with something I never thought of almost universal... Radiant Heated Towel Racks... kind of spa living at home with warm floors and heated towels...

Just about all the systems are duel and even 3-way fired... Natural Gas, Heating Oil and Wood.

TnWV · Jul 15, 2020

I definitely hope the heated floors turn out to be enjoyable. We won’t use the basement for full time living but we do have plans to regularly make use of the space.

Last pex run is complete, I’ll tidy up where they come through the floor and install the manifold this evening.

I appreciate all the advice given.
Unfortunately, I probably won’t get to see how well it works until late this winter or the following winter. I hope to be in the house by Christmas, but with the amount of work we are doing ourselves, that could be optimistic, depending on how much help I can round up throughout the building process.

I’ll get a build thread going this weekend, so anyone who wants to follow along can do so.

Thanks!