pex in-floor heat needed?

[bgarrett]

A friend way up in north Arkansas near the Missouri state line doesnt think he needs in-floor heat. He says the earths temperature is about 57 year around and didnt put insulation under his slab either. He thinks that 57 degree earth will help keep his slab comfortable.
Where is the geographical line between needing in-floor heat and not needing it?

 

[roscoe2000]

I think is is more a cost issue, most everyone would like to have it...but it is not a necessity.

 

[Randy in Maine]

Suggestion...

At least run the 2" of insulation under the slab and the 1/2 inch pex tubing in the slab. Not much money and it is there if you (or the next owner) decides to hook it up.

 

[bgarrett]

Suggestion...

At least run the 2" of insulation under the slab and the 1/2 inch pex tubing in the slab. Not much money and it is there if you (or the next owner) decides to hook it up.

Thank you for the suggestion. I am building a new place and its south of my friend but I've wondered if I need in-floor heat down here

 

[Shiftless]

I can't quite see how a guy can say the near surface of the soil around him stays at 57 all year round. Anyway, if he heats the building to over 57 the concrete will **** up some of his heat.
I live in a very mild climate and I can tell you that my 65 y.o. uninsulated garage floor is cold. (no heat or insulation in garage)

 

[PWC Repair]

Where is your friend? I'm near Mountain Home and just got my slab finished WITH tubing for heat. Check out my thread. IF you ever plan to heat it's a VERY efficient way of doing it. The average ground temp just means it won't work as hard. I've been using a buddies shop for winter projects and there is no heat at all in it. The water will never freeze but it still gets uncomfortable cold in there. I run a kerosene heater to help a bit.

 

[bgarrett]

Flippin. Thank you. You are exactly the person I want to talk to. Did you insulate under the slab? What did you use, where did you get it?

 

[bgarrett]

You may enjoy the story about the Gassville man involved in a car wreck with a woman from Flippin Arkansas. The headline said "Gassville man hit by Flippin woman!

 

[50cal]

Laying down the vapor barrier and insulation keeps moistore from wicking up

through the concrete and just makes good sense . Put the tube in for the

future. Hook it up to the manifolds and air test while pouring. Good to go.

 

[PWC Repair]

Flippin. Thank you. You are exactly the person I want to talk to. Did you insulate under the slab? What did you use, where did you get it?

I'm about 7 miles from Flippin. Plastic vapor barrier with taped seam. Then 1" "beadboard" Styrofoam. The white stuff with a foil on one side, got it at MEEKS lumber yard. I put the foil down thinking any heat that soaks through the insulation would be reflected back up. All seams taped on the foam too. Click my build thread in my sig and look at page 4.

 

[bgarrett]

Thank you, read your thread, learned what PWC stands for You will have a nice shop

 

[UpstateNY]

The white stuff with a foil on one side, got it at MEEKS lumber yard. I put the foil down thinking any heat that soaks through the insulation would be reflected back up. All seams taped on the foam too.

Bad advice - use 2" thick high-density foam blue board insulation. It's what the pro's use, anything else is ****.

 

[4cyclic]

Bad advice - use 2" thick high-density foam blue board insulation. It's what the pro's use, anything else is ****.

+1. Do it right.

 

[bgarrett]

Who sells 2" thick high-density foam blue board insulation? I dont see it at Home Depot

 

[PWC Repair]

We don't really need the 2" in our area but if you want extra then by all means go for it. There has also been much discussion about the standard vs the extruded foam. The experts report that after the extruded gasses out over a bit the R values are nearly the same. I just saw no real need to spend the extra money on the extruded. Others on this forum have also reported good results using the standard white foam.

 

[joe--h]

Bad advice - use 2" thick high-density foam blue board insulation. It's what the pro's use, anything else is ****.

Yup your advice is bad. Type II beadboard is good for under slab insulation.
Blue board or pink is good for the edge but not necessary for underslab.

As to "it's what the pros use" BS.

Joe H

 

[mygarageone]

That's why I love these forums more differant kinds of advice to make you go crazy and never get the answer you want ?

 

[Jackfre]

There was a good article in under and slab edge insulation in I think it was the Nov '16 issue of Fine Homebuilding. Radiant is nice, but pricey. It is slow to respond so don't think you will turn up the heat in the morning and be ready to go after breakfast. I chose to not do it in my building. My feet don't get cold as I wear real shoes in the shop. If you have the resources and can afford it and the other goodies you want them go for it. When I was doing a lot of radiant slabs I used to put in a few drops of oil of wintergreen, pump the system up and do the pour. If anyone smelled wintergreen it was time to find the leak...and they do happen. It the meathead factor.

 

[bgarrett]

Yeah,the original question was: Where is the geographical line between needing in-floor and not being worth it. Mountain Home Arkansas is approaching the South.I dont think anyone in Texas would want it (maybe Amarillo??) Where is that line?

 

[engineer2]

My parent retired in Mtn Home, not to far from Flippin. Remember when they had 27" of snow? Remember the ice storm where people were trapped in their homes for a week?
You can put subfloor heat on top of a slab very easily. With 57°F ground temps at least your BTU needs and heat loss won't be very big. The electric bill might be a bit higher though. IIRC, no natural gas service in that area.

 

[Kaizen]

Yeah,the original question was: Where is the geographical line between needing in-floor and not being worth it. Mountain Home Arkansas is approaching the South.I dont think anyone in Texas would want it (maybe Amarillo??) Where is that line?

the line is the one under the numbers on the check you write. my concrete for my 30x36 was 4500 approx. I priced out 2 inch blue foam and pex and it was more then a third of that price. 1800 if I remember right. i have never seen anyone use that white cheap stuff. the blue is designed to be under slabs.
so op you want to do it go for it. but i'm in nh and did not do it. other big factor for me was you cant just turn it on and expect to be warm. its a lower temp so takes days to come up to temp.....or it should if designed right. i wont be out there all week so it would be a waste to spend the money to heat it all week. if i was working out there all day all the time then i would do it.
As far as soil temp as a decision that's bogus thinking. you need to be at a constant temperature to have an effect. and the deeper you go in the south the cooler it gets. so the surface is whatever the weather is and won't do squat. esp beneath a 6 inch slab.

 

[SunsetsAndFriends]

I do this for a living. If this were my new garage/shop, I would put 2" of high density extruded foam and vapor barrier under the slab, taping all the seams. I would install 3/4" radiant flooring PEX to the foam board using plastic staples. (I would install flat wire sheets on top of the PEX with ties for reinforcement; it also provides a flat surface to walk on during the pour.) I would place the PEX at 6" centers and keep all my runs equal length and under 300' per run. Technically the runs do not have to be the same length because the manifold can balance the outputs, but I would on my own garage/shop. For 3/4" PEX the runs must be under 300'.

Pressurize the PEX with air (air compressor) and hold the pressure at 100 psi for at least 24 hours to be sure that there are no leaks. Personally, on my own garage/shop, I would be sure it holds solid for 48 hours. There are issues with expansion and contraction of the air such that the pressure will appear on the gauge to go down when it cools and up when it heats (warm day air vs cool night air) but as long as the pressure stays within the same range at the target pressure of 100 PSI, then that's good.

Keep the pressure on the lines during the pour! Have PEX couplings on hand with the PEX tooling to install them. That way if there is a blowout in the PEX lines, you can stop the pour for 5-10 minutes while you fix it. (And it will be a blowout caused by the PEX getting hit by a shovel, etc.)

As for cost, the PEX and foam board are a fixed cost but money can be saved on the powerplant. Natural gas or LP water heaters can be used to generate the heat for the in floor system. The key is that the supply water cannot be higher than 95 F. This is crucial. There are resources on the internet where diagrams or videos show how to do this.

As always, do your homework on the finer points of how to install a system like this. And talk with your local HVAC inspector for any particular considerations to your area/location.

 

[kj_mustang]

Yup your advice is bad. Type II beadboard is good for under slab insulation.
Blue board or pink is good for the edge but not necessary for underslab.

As to "it's what the pros use" BS.

Joe H

The color doesn't matter but the type of foam does. XPS is good for under the slab and on the edge. You can argue about 15 psi or 25 psi XPS being best for under slab but I went with 15 and it didn't crush as I walked on it. EPS foam, if used under the slab, should be a high density type to hold up to the weight of people walking on it before the concrete is poured.

 

[dutchgray]

Here in the UK we use either type of foam insulation under floor slabs (or cement/ sand screeds) either the better foil covered dense foam of a flooring grade of bead polystyrene (Styrofoam) we have done up to 16" of the latter, it actually works out cheaper than stone fill here and I'm only 15 miles from where the quarry's are. 2" of the foil backed is what we would use in an unheated but insulated industrial building just to future proof should it become heated or somebody builds an office in the corner.

 

[jeff_gates]

I used FOAMULAR 250 in my shop.
https://www.owenscorning.com/insulation/products/foamular-250

 

[bgarrett]

I used FOAMULAR 250 in my shop.
https://www.owenscorning.com/insulation/products/foamular-250

Where do you get it? Where you guys get high density extruded foam?

 

[James-W]

I don't know that anybody really "NEEDS" in-floor heating. There is no question that it is a very nice way to heat your shop, but there are other ways you can heat your shop besides in-floor heat. If you work out there all the time then it may be an ideal way to do it. If you only work out there occasionally then I suspect you will want to turn the heat off when you are not working out there. If you turn off the heat it will take quite awhile to get the shop back up to a comfortable temperature again. As with anything else, there are pros and cons with in-floor heat.

 

[ForceFed70]

I'm in Canada. I skipped the in-floor heat and insulation. I don't regret it a bit.

If you are like me and only turn the heat on when you're out in the shop, in-floor heat won't work for you.

I never did understand people talking about comfortable floors. Who's sleeping on their shop floors? Walking around in socks? This isn't a basement or bathroom floor. I've always got a sheet of cardboard down and a few layers of clothing between me and the floor. Never felt cold, never wished the floor was warmer.

Did the calcs - costs me less than $200/year for my shop heat. Underslab insulation was going to add $2500 to build cost. At least 30 years before it would pay off.