pex and concrete

[coolidge]

Building a garage this summer, how far apart should the tubing be in the concrete? 6" 12" I suppose i would be using half inch tubing and of course insulation and a vapor barrier. Hopefully i can fit a 28 x 40 in the location i would like, it will be sprayfoamed all the way around.

Thanks

 

[Hydronics]

It is based upon heat loss of the building. Basically -how many l.f. of tubing at a given temp are required to overcome your heat loss at design temp. Keep in mind that each loop has a maximum length- about 250'. Beyond this the water temp is nearing the slab temp and you're just creating headloss.

 

[heaterman]

Standard answer; "It depends"

Typically though a spacing of 6" for the first 3 feet in from a perimeter wall and then 12" spacing for the interior loops will get you close. If the structure is very low btu/sq ft heat loss, I have left some parts of the floor (strategically chosen) with no tube in order to be able to provide areas that have a "warm" feel to them. Sometimes the anticipation of a warm floor does not materialize because it just doesn't need that much heat flux coming up from the floor to maintain 70* air temp in the room. For example, we just fired up a system in a 2000 sq ft slab and it heats the building with 86-90* water at outdoor temps all the way down to 10*. Floor surface temp is running about 71-73* and the building temp is 68 from the floor up to the 22' peak. That floor will never feel "warm" because surface temps will rarely if ever hit 80*. Your skin temp is 85*.

Steps to a good answer for your question

1. Do a heat loss calc to find out what the btu/sq ft requirement is.
2. Consider the use of the building and decide if you want warm areas or if you want to just let the whole floor run the same.
3. Tube accordingly.

That being said.......for a garage that size run all your loops at 12" o.c. 4 loops @250' in length should do anything you need done in a garage.

 

[in hot water]

I'd consider 6" On center. The more tube the lower the fluid temperature required. 6" spacing allows you to run radiant with solar thermal in most areas. You only have one chance to tube a slab, for the extra $$ on a small to medium size shop I would "pack it in"

This graph shows how the tube spacing changes the floor output (btu/ sq. ft.)

hr

 

[djblech]

My plumber always said to use the same LF of pex as Sq Ft of the slab. I usually put it closer around the perimeter where the greatest heat loss will occur. If 1 ft footing I stack 2 runs up and down. The center can be spaced wider as it will hold heat longer. I did my brothers 40 x 80 x 12 and it heats almost to easily.
Doug

 

[jebatty]

Sometimes the anticipation of a warm floor does not materialize because it just doesn’t need that much heat flux coming up from the floor to maintain 70* air temp in the room.

Ditto. I have 6" oc for the first 3 feet and 12" oc for balance, 32 x 48 slab, 14' sidewalls, insulated with R19-6" fiberglass in walls and R39+ in ceiling. 2" foam under the entire slab, 2" edge perimeter, and 2" down 30" around the perimeter. This being a shop, I set the in-floor sensor at 61F, 1F differential, and left it there all winter. Supply water at 100F+/-. Very comfortable inside working temperature, draft free.

Floor sensor: constant 61F (1F differential)
Outdoor/Indoor air temperature:
+ 20F / + 58F
+ 10F / + 57F
0F / + 57F
– 10F / + 55F
- 20F / + 50F )
- 25F / + 50F ) in this range about 2 weeks during the winter
– 30F / + 47F )

 

[ChiefChicken]

Just remember to take lots of reference pictures if you think you might ever want to install something like a floor lift.

 

[711mhw]

Building a garage this summer, how far apart should the tubing be in the concrete? 6" 12" I suppose i would be using half inch tubing and of course insulation and a vapor barrier. Hopefully i can fit a 28 x 40 in the location i would like, it will be sprayfoamed all the way around.

Thanks

In my shop (in Maine also) my spacing was 18". I had a company called Northeast Radiant in Gardiner (ME) do my design work and have been very happy with there services and they can supply all the related parts as well. They will want to do heat loss calcs. as others have stated.