Spacing @ 12" for Snowmelt using 3/4" Hepex OK?

Temblor

Hi installing Snow melt in North Seattle area using 3/4" Uponor Hepex.

9x24 (216 sq ft) basement garage driveway (Medium grade with channel drain at bottom)

4" Concrete

Using 2" rigid insulation under and around perimeter. 

Manual timer system.

I have a 230' of 3/4" existing material I am hoping to use. So I am considering putting the heat exchanger near garage (which is about 35' from boiler)

So I will have to insulate the 35' run?

My main question is:

Would this be a sufficient amount of pipe? Can I use 12" spacing  O.C.?

Thanks in advance!

Zman

Good plan

I don't see a problem with the tubing size, length or layout. Yes, I would insulate the supply and return lines to the exchanger. As always be sure the tubing does not end up on the bottom of the slab and route your tubes so the drain won't freeze.

Mark Eatherton

Yes, but....

Snowmelt is typically done at 9" OC to keep BTU/Sq Ft density high (150 btuh/Sq ft here in Denver). All of this is dictated by the local climatic conditions. Uponor has all the parameters necessary to determine spacing, flow, temperatures etc.



12" OC will provide snowmelt, but you can expect some striping to occur, which is no big deal.



As for length, at 12" OC, you'd calculate the amount of tubing required by multiplying the active area times 1.15. The .15 accounts for the tubing consumed in the bends.



So, in your case, 216 Sq Ft times 1.15 = 248 linear feet of active, in slab tube. This means you are going to have to determine what area doesn't get melted. Pick that are that will naturally see sunshine.



Go light on the glycol. but no less than 30% for corrosion inhibition. And yes, insulate all lines (it is the code here in CO)



ME

Henry

Design

Uponor will do the design for you IF, you are a contractor.

RobG

snowmelt layout

My preferred method of a snowmelt layout is to go concentric on the supply at 18" and then eccentric on the return from the center of the loop making the system 9" on center overall. I can't remember the name of the design layout but it alternates the supply and return every 9". It has always worked well for me and I have never had striping issues. It also makes the only true 180 degree bend in the center of the layout, and with 3/4" pex, the bigger it is, the more difficult it is to bend. 

Rob

Mark Eatherton

Reverse return counter flow???

I think that is the method you are talking about Rob, and as long as you have plenty of tubing, it works well. But if you have a limited amount, as Temblor has, you might run out of tubing before you get back to the manifold box.



I've always ran my tubing in a serpentine manner, and I've never had any issues with striping or non melt areas, but I also maintain tubes at 9" OC, and strive for a 15 degree delta T.



ME

Zman

All good info

But I am still good with Temblor's plan given that it is an occasional use residential job in Seattle. He is obviously doing it on a budget otherwise we would be talking tekmar controls and idle temps.

NYplumber

Two loops

The single loop should work, however, being that this is a small pad and a timer system, you should consider two shorter loops on 9" centers to get the instant feedback that most homeowners with timers expect. With the two loops you also have the option to melt additional walking space.