Heat trap or swing check

hiker88 · Oct 4, 2012

I recently re-plumbed my oil furnace to incorporate my Froling. Previously, I had a taco pump that was connected directly to the boiler on the return side. So, if you were in my basement in front of the oil furnace, the lines from my heating zones came down through the ceiling, into a manifold up around the first floor joists and then ran about 5 feet or so down in 1" copper pipe, turned 90 degrees, through the circulator pump, and into the boiler.

I now have an alpha pump that is on the supply side of the boiler. I removed the old pump on the return side and just replaced it with a straight piece of pipe with flanges.

I've noticed that the long stretch of copper pipe on the return side of the boiler gets pretty hot (120-130f maybe or more) even when there is no call for heat. I've put my hand quite a ways up the pipe and it is very warm. Since the zone valves aren't open (and haven't been for days) when I noticed this, I figure hot water must be "backing up" out of the boiler and into the return pipe. I don't know if it has always been this way and I just noticed it - or if by relocating the pump I've caused this to happen (maybe it had a backlow preventer?).

I'll be taking the oil furnace off line in a couple days to incorporate the dhw coil in my storage tank into the house supply, so that would be a good time to fix this issue (if it is an issue).

I'd appreciate your thoughts about the right way to fix this if it needs fixing. If I missed a solution, please let me know.

p.s. When I say heat trap, I'm thinking of doing something similar that I did on my storage tank - a u shaped design w\pipe.

Thanks!

BHetrick10 · Oct 4, 2012

Let me get this out of the way first.

I am not a boiler professional.

I have seen similar situations at domestic water heaters. There isn't check valves and such on them. Some plumbers will put a heat trap on them. What I have noticed is that if hot water hasn't been ran for a while and there is a check valve from the city at the meter this will happen. Solution is an expansion tank.

I hope you have one in your system. Maybe its water logged and HWB the boiler will have the most head. Hence the pump at the return. If you have radiant it will have more head than your boiler.

Reread second sentence...

hiker88 · Oct 4, 2012

The expansion tank doesn't seem to be waterlogged; it has a good ring to it when I tap it and doesn't seem heavy enough to have any significant amount of water in it. Here is a schematic of my system - I actually have two expansion tanks.

RobC · Oct 4, 2012

Once you get your Froling running for the winter do you leave your OB online also ?
Mine has the potential for auto back up but I manually switch electrical supply off and close supply and return ball valves almost completely. I leave valves open a crack to keep pressure up and get a little flow through OB.
Another solution would be to insulate pipes.
I guess I would try to keep it simple with out check valves if possible.
There is a spring loaded check valve. You might want to look at them. Look at instructions for checks. I recall some can't be installed vertically etc.... Swing checks won't work facing down, swing will just hang open....
Do a search on checks, HR wrote in discussing this topic....
Heat trap. That will work if it's only thermal heat. They prevent heat from rising up the pipe. If there is any sort of back pressure from changing circulators or " ghost flow" the heat trap won't work.

R Mannino · Oct 4, 2012

Does your Alpha have the flow check installed in it? Pictures of the boiler would be a little more helpful.

Bob Rohr · Oct 4, 2012

R Mannino said:
Does your Alpha have the flow check installed in it? Pictures of the boiler would be a little more helpful.

It is possible for thermosiphoning to occur in piping systems. Lower density, hot water rises, the cooler water drops. This is how a thermosiphon solar system operates. It is hard to predict when thermosiphoning, aka ghost flow will occur or how much flow. Certain piping arrangements seem to encourage it, like piping that rises straight up off a primary/ secondary loop. Sometimes a circulator with an internal spring check will be enough to prevent it.

It is possible to have two direction flow up the return piping, even with a check on the supply side. Hotter water travels up the center of the pipe, cooler water drops down the side. In some cases it is necessary to install a check on both supply and return piping. A basic swing check is not the best choice, they can chatter if insufficient flow is passing thru them to keep the gate open. variable speed pumps will not get along well with swing checks. they were really designed for pressure systems, like your well or sump pump

Either a spring check designed for hydronic applications with a soft seat, or a weighted flow check designed for hydronic applications. The spring checks seem to be the way the industry is going. They are available in the pump body, or in the isolation valve/ flange, or buy them as a separate component.

Mother nature hates an imbalance and will always allow hot to go to cold, it is the basic principle of thermodynamics. The greater the temperature difference the more potential for heat transfer.

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Heat trap or swing check

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