1/2" or 3/4" pex radiant floor tubing?

[matouse3]

I am going to build a 32x40 garage, slab with radiant heat. The layout and floor plan can be found here:
http://garagejournal.com/forum/showthread.php?t=138758

My question is whether I should run 1/2" or 3/4" pex and if it matters. I was originally planning on 1/2" but have found some conflicting information. My layout calls for about 1250ft of 1/2", for the 1280' floor space, which seems correct.

My other question is whether I should run antifreeze in the system? Badger has already commented that it will take more energy to run, and in another post of his, he prefers 3/4" for antifreeze, which is another reason I am questioning my 1/2" choice. I am assuming that 3/4" is preferred since you would have shorter runs.

Any and all comments are appreciated. Thanks!

[Randy in Maine]

I opted to run 1000 feet of 1/2" in my 40'x 28' garage.

[chickenhauler]

I've run both, and honestly, I can't tell the difference in performance. 1000 +/- feet of 3/4" in the main part of the house, then I used 1/2" when I did the master bath. Mine is in the house though, no antifreeze.

[Jackfre]

I'd run 1/2". Just keep your loop lengths around 250'. You don't say where you are. If you are way north then glycol is ok, but I'd try it without it. I'd rather have a low temp warning alarm on the system than add anti-freeze. You have to maintain antifreeze and it increases the fluid viscosity, which requires more pump hp

[matouse3]

Thanks guys. I am in mid-Michigan. We get some pretty cold spells here (not this year), but I plan to sock the insulation to the building to help with that.

[Novicaine]

One 1/2" loop (max 250') can transfer about 1-2 gpm MAX to the floor. 1 gpm can transfer about 10 Kbtu/hr. So your 5 loops will be able to pump about 5-10 gpm or about 50k-100k into the floor. But you'll need a decent circulator pump to move that much gpm (see below). If you went with 3/4" (or even 5/8") that'd reduce the circulator load and make it easier to pump more BTUs.

A 250' loop of 1/2" pex at 2GPM will need a pump to overcome 42' of head.
A 250' loop of 1/2" pex at 1GPM will need a pump to overcome 12' of head.
A 250' loop of 5/8" pex at 2GPM will need a pump to overcome 16' of head.

So, IMO, 1/2" will do the job, but it is on the edge of it's limits. You have more to "room to play" with 5/8".

I have 5 loops of 300' 1/2 pex and my circulator (Grunfos 15-58, less than $100) is only moving about 3.25 GPM (at roughly 24' of head), and I was targetting higher. My loops are too long, granted. But I would have had more room for error had I used 5/8. I am going to try a larger circulator someday, see if I can get my GPH up a little more, but it's going to be tough in the 1/2".


References:
http://www.taco-hvac.com/uploads/Fil...irculators.pdf

[hercules633]

NOVACAINE- what size is your radiant floor pad? roughly 1500? 32x48? thanks

[Novicaine]

Originally Posted by hercules633

NOVACAINE- what size is your radiant floor pad? roughly 1500? 32x48? thanks

33x48, and I am running 50% antifreeze, well, not car antifreeze, but the stuff for in-floor heating.

[hercules633]

NOVACAINE- thanks, I am looking at the same size 32x48 and want to do the radiant. so it looks like you would have went with the 5/8s if you had a do over on your system? got any pics of your garage and system installed? and a rough estimate of the cost to do the complete radiant system?

[Novicaine]

Originally Posted by hercules633

NOVACAINE- thanks, I am looking at the same size 32x48 and want to do the radiant. so it looks like you would have went with the 5/8s if you had a do over on your system? got any pics of your garage and system installed? and a rough estimate of the cost to do the complete radiant system?

5/8" would have been smarter. And definitely keep loops under 250', and my pex was spaced every 16", 12" would be better. Again, a miscalculation on my part. So in a perfect world, you'd want 7 loops of 250-ish 5/8" pex. But 5 300' loops of 1/2" do work also. I keep the shop around 60 degrees, and in central Illinois our winters have been mild.

The other thing I'd recommend: Pour the slab before building the shop! (Or ask your builder about it) I didn't know you could do that until afterwards. That would have made so much better: No poles rotting in ground, no boards showing on the lower sides of building, no gravel backfil around the building. Digging the footings for overhead doors after shop was up was a royal pain. Leave an area un-poured though where services come in to building for future expansion.


Here's some pics of mine going up and the tubes:

https://picasaweb.google.com/1078259.../New33x48Shop#

Here's a link to a post with pics of my system:

http://www.garagejournal.com/forum/s...ad.php?t=85050

As far as cost ... I forget... boiler was $1200? Pex I forget. The manifolds and copper and pump, air strainer, etc, maybe another $1000 - $1500. I only use 48K btu of my 120K btu boiler, so I could have went smaller there.

[BadgerBoilerMN]

To clear up some confusion.

You could use 3/8" PEX if you wanted a bigger manifold.

We rarely use 3/4" PEX for smaller shops or garages. It is not about performance, so much as, time and material.

We use 1/2", 5/8 and 3/4" PEX for snow melting (all with outputs about 3 times the heat load of the average building here in Minneapolis) but for most garage/shop buildings under 10,000 sq.ft., 1/2" is the standard. The length of tubing is dependent on the design flow and specify gravity of the heat transfer fluid.

For example: 250' for 5/8" (rarely needed or used) is shorter than most applications would need requiring more loops and consequently a bigger - more expensive - manifold.

There is no radiant floor heating application in the "Lower 48" that requires a true 50/50 mix of propylene glycol anti-freeze, save a commercial snow melting system in the coldest of climates.

We design radiant floor heating systems and provide all the specifications including a CAD drawing...no WAG involved.

[coachschaefer]

How has your radiant worked out? I am building a 30x40 garage and not sure what I should install. 1/2" or 7/8". I am also unsure of the amount of loops,etc? Any help would be great!

Mike

[Highbeam]

1/2" tube is the standard which makes anything else odd.

[kvom]

I used 3/4" 3 loop, but 1/2" 4-loop would have been easier. The 3/4 was quite hard to uncoil and needed 2 people to prevent it kinking. I tried to lay it myself solo and got a kink right away. Once kinked that section of tube is toast.

[wedge40]

Originally Posted by kvom

I used 3/4" 3 loop, but 1/2" 4-loop would have been easier. The 3/4 was quite hard to uncoil and needed 2 people to prevent it kinking. I tried to lay it myself solo and got a kink right away. Once kinked that section of tube is toast.

I'd slide a small piece pvc conduit over the kink. Just a my :2cents:

Wedge

[matouse3]

Kinks in pex a tubing:

https://www.youtube.com/watch?v=lgWIbDLn4Kg