Hydronic driveway advice

Skender823

Hello I could use some advice. The first owner of my house put in the start of a hydronic heated driveway system. The garage has a manifold with 4 loops for a driveway that is about 240 sq feet. I have pressure tested the system so I know that it holds pressure but the system is missing circulator pumps and an expansion tank. I am going to describe the setup and then include some photos:
There is a 50 gal Powerflex power vent water heater. The water heater is about 6 feet from the heat exchanger, two copper pipes come off of the side of the water heater run up to the ceiling and then over to the heat exchanger so close to 12 feet of 1/2 inch copper pipe. After the heat exchanger there are a red and blue pex pipe that run to a wall 12 feet away then into the garage where they are wrapped in some foam insulation and travel along the garage wall to a 4 zone manifold. So I've been trying to do the math and calculate gpm and head loss, my work shows a gpm of 7.2 on the manifold side with a head loss of about 10 but I really don't know if that is right. I'm also not sure how to figure out gpm and head loss for the water heater loop, and I have no idea how to figure out how big of an expansion tank I need. I can get some grundfus alpha1 15-55fr for $90 each and I think that will give me what I need but I'm not sure.

GroundUp

The Powerflex is only about 45,000 BTU output which is about enough for 225 square feet of good snowmelt. It looks to me like it's currently serving the DHW function in your house, so freezing at the HX is a distinct possibility and you'll have no domestic hot water whenever the snowmelt is running. Unless you know the loop lengths, there is no way to calculate head loss on the manifold side but 7.2 GPM is most likely pretty high regardless.

This is not a good idea. If you want the snowmelt, get yourself a dedicated heat source.

hot_rod

When the snowmelt is on, I doubt you will get any hot water for the house. It's fairly small for both loads. it could be in melt mode for hours. Or days

As groundup suggested, you need a separate dedicated heater for the snowmelt.

Skender823

Thanks guys like I said the set up was there before so I assumed it would be set up at correctly.

hot_rod

The good news is it looks like plenty of tube is installed. As far as heater sizing, it really comes down to how quickly you want to melt? Like an engine selection in a truck, what's the load.

Basic snowmelts can run 100 BTU/ sq. ft. I've seen some slow performing ones work at 75 BTU/ sq. ft.

Critical applications like helipads on hospitals may have 200 BTU or more/ sq. ft.

So your heater would work okay, it just would not give you domestic hot water when locked into melt mode.