In Floor Radiant Heat

[Cartw1]

Hi all, new here and appreciate any feedback!
I am set to constuct my garage. It has been a long haul with applications for a minor variance, permits, bank financing etc...but tomorrow the concrete contractor arrives.

I have some ?'s re: in floor heating

a little info: the garage will be a 20x30' Gambrel Roof, 2 story with full poured footings, 8" poured walls and 4" slab floor. I live in Ontario, Canada so a building with proper footings and foundation is desirable due to freeze/thaw cycle and structural integrity.

I have decided to install 1/2" pex line, heated water, in floor radiant heat system. The local Home depot offers a product from "Plasti-Fab" which is a 2 1/2" rigid foam board with foil on one side and grooves cut in to place your pex. After that, the pex is stapled in, covered with wire mesh and the cement poured over that.

That is the extent of my understanding. have any of you constructed with this type of materials? any comments or suggestions..I would really appreciate it

Thanks again,

Jay

 

[60vett]

I have a similar garage, and I would recommend 3/4 or 1" pex minimum

 

[z28toz06]

I think the max length on 1/2" is like 300 feet per loop. You wont get too far and will have quite a few loops to heat that correctly. Go with a bigger pipe.

 

[Racecarl]

I am building a 24X30 and will run 3 'zones' of 1/2" pex. Placing the pex on one foot centers will result in 3 zones with 238 feet in each one. I will be running my zones the 30' length of the shop with no curve at the ends less than a 2' radius. The tubes at the ends will either overlap a little or run pretty close together for a foot or two, but the middle should have pretty uniform distribution.

 

[Cartw1]

I am satisfied that 1/2 " will be fine. My cousin heats his 44x70' shop with 5 300' loops of 1/2 inch and does just fine.Some write ups on line recommend that the 3/4 and 1" pex can actually be less efficient ...what I am more interested in is the insulation material underneath...what are you guys using, how are you tying it in, and what about wire mesh...over pex or under?

 

[stevemcwilliams]

The mesh goes on top of the insulation I would use 2 inch high density blue board place 6"x6" 10 guage wire mesh and then use plastic zip ties to hold the pex pipe in place. I had done many that way and it seems to be the most cost effective. 300 feet runs of 1/2 inch tubing is a little long but will work. I think the calculations of line lose dictates runs closer to 200 feet. Depends on how many turn backs you have (bends)

You will like that heat.

Steve

 

[Kapt]

I used 2" DOW scoreboard with 1/2" rebar and 1/2" pex zip tied to the rebar. My garage is 24X26 and I run 2 loops and it works fine.

 

[Cartw1]

great , thanks for the replies fellas....KAPT, looks like you have done some insulating along your foundation walls as well......how far down the wall have you gone with that? thanks for the pic

 

[jopickens]

My shop is 40x64 with a 6" + concrete floor. Four ~400' loops of 3/4" pex on 20" spacing. I only wish now that I had used 5 loops with closer spacing and possibly slightly shorter length loops. Obviously this is my first in-floor heat rodeo. Only saving grace is a gas well on my property - free gas.
Hopefully get it hooked up this fall... have been using a couple 100,000btu unit heaters temporarily last couple years. I have everything to hook up the radiant heat minus the pump (need to do some research on which model fits my scenario). I have several boiler/heater options... Doing this low-buck of course. One of the free options is a like new 300,000btu pool heater. Anyone heard of using a natural gas pool heater for in-floor radiant heat??? I know there is more to it than meets the eye... but we're simply putting heat into the water, circulating it through the floor - allowing that heat to transfer into the slab... repeat over and over? Of course at this point I've got no choice but to give it a shot...

Josh

 

[jrz]

I have seen infloor systems using small (40 Gallon) gas water heaters.

 

[Cartw1]

mine will use a "tankless electric water heater" about the size of an encyclopedia hanging from the wall.....ever heard of K.I.S.S (keep it simple smartguy
thanks for the pics JOPICKENS..but I only wish I had a gas well on my property!

 

[Kapt]

The insulation extends only about 6" down the foundation walls. Having to do it again, I probably would have gone down a little more. A lot of people recommend insulating the outside of the foundation walls.

Here is a picture of my tankless electric setup. Works great.

 

[jopickens]

Hey Kapt that looks great! I guess I could emulate what you did with an instant/tankless natural gas hot water heater. What size pump is that?

Josh

 

[Cartw1]

ya Kapt...that is sweet...exactly what I will do...only I will likely have 3 loops. Very very well done. yours looks really nice

 

[e-tek]

Sweet shop Mr Pickens!

 

[dhubz]

anyone used spray foam on the floor instead of the foam board. The guy I was talking to mentioned using water blown. I realise cost is the biggest issue, but I can get a good deal on it. I've googled it but can't find any sites that have info on spray foam on the floor, either 2lb close cell, or water blown. Any help is appriciated, I have limited time to jump on this offer.

thanks

 

[CBR9Seadoo]

This is great. I am getting ready to build a 24' x 40' addition on my shop and plan in floor heat as well. I am putting Dow Formular 250 2" thick below my slab and lining my foundation with Formular 150 2" to keep the heat from radiating out.

My question? Does anyone know of any freeware software to help design my loop layout?

Thanks,
Tim

 

[Possum]

Do a google search for LoopCAD.

 

[nate379]

You'll be fine with 1/2". My garage, 24x26 is heated with 1/2" Pex. 3 loops.

 

[ixlr8]

Keep the loops about 1 ft apart, limit the loop length to 250ft max per loop, if running 1/2" PEX and you should be fine. You can run longer lengths if you use larger diameter tubing... if you use smaller diameter tubing, loops will have to be shorter. Have you done heat loss calculations so you know how hot the water will need to be to provide the needed BTU's?

 

[klutz]

Cartw1
I have researched radient heating as well, and with Ontario winters, I have learned that using 2" insulation down the inside of your walls is critical. Trick is to rip the top edge (of the insulation) on a 45 degree angle, snap a chalkline where your floor will be, and place the long side of the 45 to the chalkline... and run the insulation down the wall a minimum of 2 feet.
And if Pex is used in more than 300 foot lenghts, you'll need a pump. -go 1/2"-

 

[babzog]

Cartw1
I have researched radient heating as well, and with Ontario winters, I have learned that using 2" insulation down the inside of your walls is critical. Trick is to rip the top edge (of the insulation) on a 45 degree angle, snap a chalkline where your floor will be, and place the long side of the 45 to the chalkline... and run the insulation down the wall a minimum of 2 feet.
And if Pex is used in more than 300 foot lenghts, you'll need a pump. -go 1/2"-

So you have the foam insulation pretty much at the top of the slap at the slab/wall junction? Why should the insulation be carried up that high?

 

[klutz]

yeah, thats how my contactor explained it, but I may go about 3" below the level of the floor. I'm not building til spring, so I should find out the details before then. Maybe some ideas from the pros would help.

 

[rburke65]

On This Old House I saw them using the "Plasti-Fab" underlayment with the Pex as you described.....in a $ BIG BUCK $ house in Mass. Those guys were "talking it up". Looked like a nice product to me, but I have never used it. Good lick.

 

[tdkkart]

So you have the foam insulation pretty much at the top of the slap at the slab/wall junction? Why should the insulation be carried up that high?

The whole idea of the insulation is to isolate the slab from the cold ground and air, so you want everything insulated except the surface that you want to the heat to radiate from.
The heat radiates from all surfaces of the slab, top, bottom and sides, however you will only benefit from the top side, so you want to minimize radiation in all other directions as much as possible.

I'm just finishing up a 30 x 40 pole building that was built by the previous owner and then left without interior finishing.
First order of business was to dig a 24" deep trench around the interior of thebuilding, inside of the poles. In this trench I installed 2" foam board vertically, making the top edge at the level of the finished concrete. The foam board actually acts as the cement forms above ground level and inside the posts. Yes, I ended up with a 2" pink border on the outside edge of the concrete, which is taken care of in the next step.

In the last fw weeks I've insulated the walls, R19 fiberglass, and then a layer of 1/2" foam board over the whole works, floor to ceiling. Around the bottom of the walls I installed a treated 2x6" as a base board. The 1/2" foam board combined with the 2x6 covered the previously mentioned 2" pink stripe at the edge of the floor. The walls and ceiling were then sheeted with white pole building siding.

My slab is now completely isolated on all sides from the outside world down to a depth of approx. 20" below ground.

 

[babzog]

Hey tdkart,

Thanks for sharing that. I'd seen other guys here form up their slabs in that fashion too and wondered about if/how any exposed foam was concealed, but never saw a good finished pic that showed what was done. I guess, a small skim layer of concrete on top of the foam wouldn't hurt much, but I like your notion of simply hiding it with wall.