Help with heated driveway set up

Skender823

Hello I have read through a few of the posts on hydronic systems and done my own but am still a little lost and looking for 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.

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.

I actually posted this on the Terry plumbing site a while ago and someone directed me here. Someone suggested my hot water tank is not big/powerful enough for this job. I've been trying to do some research to find out if there is some kind of closed system hotwater heater I could hook up to the heat exchanger but I'm not sure if that's a thing or if it would work. I will take any advice.

Jamie Hall

Domestic hot water heaters, such as the one you have, are wonderful — for domestic hot water. They are not intended to provide heat for a building, never mind a snow melting system. Wrong tool for the job.

It takes a lot of heat to power a snow melting system, and someone else will chime in here with how to calculate how much. Then you need a power vented boiler — there are many good makes out there — to provide the heat. From there figuring the pumps and plumbing is pretty simple.

hot_rod

240 sq ft x 100 btu/ sq ft would need 24,000 btu/hr. A common water heater would cover that

A heat exchanger would isolate the loops so you don’t need so much glycol

What size are the loops? Diameter and length?

Skender823

@ Jamie Hall might be a stupid question is there a differance between a boiler and a hot water tank? The one I have is power vented and has extra inlets and outlets.

@ hot_rod all I know are the loops are made of pex probably an inch in dia, and there is a heat exchanger on the wall. I don't have much info beyond that.

ratio

See if you can read any printing on the side of the pipes. That and some pics of what you've got will be a good start.

hot_rod

Got some pictures? 3/4" pex is 7/8" outside, that would be good for snowmelt. Is the water heater in a place when it will not freeze? It will have plain water in it.

With a heat exchanger, you will have two pressurized systems. So two pumps, two air seps, two expansion tanks, two sets of valves, relief, fill, etc.

So after pricing all the components, it could be cheaper to just connect the tank and glycol everything?

Especially if the tank or any piping is in a area where it could freeze. Leaving the garage door open, by mistake is a common freeze call.

A pic of the two options

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Skender823

@hot_rod thanks it is set up like your top picture. In the first picture you can see the red and blue pex tubing coming from the garage on either side of the air vent. The next few are of the hot water heater and then one of the heat exchanger on the wall. The manifold is in the garage I'm guessing that would be where it is refilled too. The last picture is just a closer picture of the pex coming in from the garage. Bases on your drawing I'm missing two pumps and two expansion tanks and need to check if the manifold has a relief valve on it, if not I'll need that too. Any advice on the set up so far, I didn't set it up in the first place so it looks right to me from what I've researched but I don't know what I don't know. I never even thought of the driveway side of the system needing a relief valve.

hot_rod

the hw tank is just for the snowmelt, correct? It is not supply water to the home?

Looks like it has additional side connections, you only need to use two. The top one behind the relief valve, and the bottom one where the ball valve is. Why the capped tee off the drain port, the yellow valve? Are you running some radiant heat also?

That snowmelt will take all the heat that 40,000 tank can provide. So you would not have any extra when it is in snowmelt.

You can also build a glycol fill tank with a #30 expansion tank to maintain pressure in the glycol loop as air comes out

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Skender823

It looks like the original setup was to use one water heater for home and snow melt maybe thats why it was never finished he realized it wouldn't work. I have no idea what the capped off pipe is for. So for a second water heater for just the snow melt what would u suggest?

Jamie Hall

A real boiler. Sized for the job — 100 BTUh per square foot perhaps. Not a water heater.

hot_rod

240 sq ft of snowmelt at 125 btu/ sq ft = 30,000 btu/hr.

I think you have this WH, a 45,000 btu/hr input

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At 80% efficiency you get 36,000, so plenty of power for that size snowmelt.

125 btu/ sq ft is the line between class 1 and class 2 snowmelt, plenty for residential systems in most areas.

How many days a year will you be melting? I'd be inclined to use the WH for the melt, since you own it, get a small boiler which gets more hours per year for the heat and DHW.i

A drum of 40% glycol may cost 6- 800 bucks. Or use the plate HX you have and maybe 8- 10 gallons of glycol. But you need two pumps, expansion tanks, air seps, etc. So the cost may work out about the same to glycol the tank and system or build the HX interface.

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