Welcome to the The Garage Journal Board forums.

You are currently viewing our boards as a guest which gives you limited access to view most discussions and access our other features. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join our community today!

If you have any problems with the registration process or your account login, please contact contact us.

Go Back   The Garage Journal Board > The Garage > Heating and A/C

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Search this Thread Display Modes
Old 02-21-2012, 01:22 PM   #1
matouse3
Senior Member
 
matouse3's Avatar
 
Join Date: Feb 2012
Location: Mid-Michigan
Posts: 286
Default 1/2" or 3/4" pex radiant floor tubing?

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!
matouse3 is offline   Reply With Quote
Old 02-21-2012, 08:59 PM   #2
Randy in Maine
Senior Member
 
Join Date: Nov 2010
Location: The Beach
Posts: 575
Default Re: 1/2" or 3/4" pex radiant floor tubing?

I opted to run 1000 feet of 1/2" in my 40'x 28' garage.
Randy in Maine is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 02-21-2012, 09:27 PM   #3
chickenhauler
Senior Member
 
chickenhauler's Avatar
 
Join Date: May 2011
Location: Pennsylvania
Posts: 436
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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.
chickenhauler is offline   Reply With Quote
Old 02-21-2012, 10:03 PM   #4
Jackfre
Senior Member
 
Join Date: Dec 2010
Location: N CA
Posts: 895
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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
Jackfre is offline   Reply With Quote
Old 02-22-2012, 07:31 AM   #5
matouse3
Senior Member
 
matouse3's Avatar
 
Join Date: Feb 2012
Location: Mid-Michigan
Posts: 286
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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.
matouse3 is offline   Reply With Quote
Old 02-22-2012, 01:41 PM   #6
Novicaine
Member
 
Join Date: Oct 2010
Location: Central Illinois
Posts: 50
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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
Novicaine is offline   Reply With Quote
Old 02-22-2012, 07:38 PM   #7
hercules633
Junior Member
 
Join Date: Jan 2012
Posts: 16
Default Re: 1/2" or 3/4" pex radiant floor tubing?

NOVACAINE- what size is your radiant floor pad? roughly 1500? 32x48? thanks
hercules633 is offline   Reply With Quote
Old 02-23-2012, 01:26 PM   #8
Novicaine
Member
 
Join Date: Oct 2010
Location: Central Illinois
Posts: 50
Default Re: 1/2" or 3/4" pex radiant floor tubing?

Quote:
Originally Posted by hercules633 View Post
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.

Last edited by Novicaine; 02-23-2012 at 01:28 PM.
Novicaine is offline   Reply With Quote
Old 02-23-2012, 03:10 PM   #9
hercules633
Junior Member
 
Join Date: Jan 2012
Posts: 16
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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?
hercules633 is offline   Reply With Quote
Old 02-24-2012, 01:16 PM   #10
Novicaine
Member
 
Join Date: Oct 2010
Location: Central Illinois
Posts: 50
Default Re: 1/2" or 3/4" pex radiant floor tubing?

Quote:
Originally Posted by hercules633 View Post
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.
Novicaine is offline   Reply With Quote
Old 03-13-2012, 01:37 PM   #11
BadgerBoilerMN
Senior Member
 
BadgerBoilerMN's Avatar
 
Join Date: Aug 2011
Location: Minneapolis
Posts: 507
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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.
BadgerBoilerMN is offline   Reply With Quote
Old 11-05-2012, 07:43 PM   #12
coachschaefer
Junior Member
 
Join Date: Jul 2012
Posts: 2
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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
coachschaefer is offline   Reply With Quote
Old 11-06-2012, 11:23 AM   #13
Highbeam
Senior Member
 
Join Date: Feb 2011
Location: South Puget Sound
Posts: 1,817
Default Re: 1/2" or 3/4" pex radiant floor tubing?

1/2" tube is the standard which makes anything else odd.
Highbeam is offline   Reply With Quote
Old 11-07-2012, 10:10 AM   #14
kvom
Senior Member
 
Join Date: Feb 2008
Location: Cumming, GA
Posts: 817
Default Re: 1/2" or 3/4" pex radiant floor tubing?

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.
__________________
'02 F350 PSD - tow pig
'97 Jeep TJ offroad buggy
'00 Jeep TJ street legal crawler
'08 Kia Sprint5 - for getting around
'12 Chrysler 200 - wife's grocery getter
kvom is offline   Reply With Quote
Old 11-08-2012, 05:58 AM   #15
wedge40
Senior Member
 
Join Date: Oct 2009
Location: Bloomington, IN
Posts: 330
Default Re: 1/2" or 3/4" pex radiant floor tubing?

Quote:
Originally Posted by kvom View Post
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
wedge40 is offline   Reply With Quote
Old 11-08-2012, 07:40 AM   #16
matouse3
Senior Member
 
matouse3's Avatar
 
Join Date: Feb 2012
Location: Mid-Michigan
Posts: 286
Default Re: 1/2" or 3/4" pex radiant floor tubing?

Kinks in pex a tubing:

https://www.youtube.com/watch?v=lgWIbDLn4Kg
matouse3 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 04:48 AM.