How much PEX do I need?

[chadman]

I am going to be installing PEX in the floor of my new garage and I have a few questions. Garage will be approx. 1000 square ft. with R-14 walls and R-29 ceilings. One 16ft. and one 10ft. door both R-11. There will be 2" of XPS insulation under the slab. My questions are:

1) 1/2" or 3/4" PEX?
2) how many feet of PEX do I need?
3) how long per loop?

 

[walrus]

I am going to be installing PEX in the floor of my new garage and I have a few questions. Garage will be approx. 1000 square ft. with R-14 walls and R-29 ceilings. One 16ft. and one 10ft. door both R-11. There will be 2" of XPS insulation under the slab. My questions are:

1) 1/2" or 3/4" PEX?
2) how many feet of PEX do I need?
3) how long per loop?

I;m sure someone will protest but the rule of thumb is 1 ft of pex for every sq ft of slab, 1/2 pex no more than 300 ft in a loop.

Where are you located, might make quite a difference?

 

[chadman]

Thanks for the reply. I am in notheast Ohio between Sandusky and Cleveland.

 

[Dragster Racer]

I would agree with Walrus from what I have read, and what we did in our home. If anything, you could go a little more than 1/sq since you have a little less insulation than a home and quicker recovery would be nice. Just set your tubes less than the suggested 1' apart. There isn't a lot of science to it. It's pretty forgiving.

 

[Rob_b]

Thanks for the reply. I am in notheast Ohio between Sandusky and Cleveland.

Chad, I saw on a show we have here north of the border that the contractor installing the in floor heating used a styrofoam that had disks where the pex would be routed through and be lower than the tile or whatever other flooring was used. He used this stuff as a thermal break so your not heating below the surface and all the heat travels upwards where its needed. It wasn't very thick but very effective and required zero clamps to hold the pex piping. It held it by friction. Also if you use a manifold, it may make it more even heating but I assume you were going to use it anyways. Good luck

 

[GearBeer]

There's no substitute for laying out your tubing pattern to figure out how much you need. I made a spreadsheet to guesstimate this and came within 1' of what we used.

I made every other column and row thin and used colors to fill them to denote the routing. In the wide columns I inserted the distance center-to-center of each pair of adjacent tubes.

 

[baugie]

Hey Chadman:

I'm due north of you on the other side of Lake Erie.
1/2" pex will do....make sure it is the oxygen barrier type. To calculate how much pex you need........use this formula....square footage of the floor + 20% = amount of linear feet of pex needed......divide that number by the amount of feet per roll and that's how many rolls you will need. I just finished my garage and the formula was quite accurate.
NOTE: do not have in splices in the concrete. My loops were 250 ft long.

 

[walrus]

You want to keep each loop within 10% in length also

 

[chadman]

Thanks for the info. What spacing are you all using?

 

[baugie]

first two outside loops 6" apart. then you can go from 8" to 12" as you get closer to the center.