I have an oil fired boiler in the basement. I have recently installed a coal fired boiler in a garage and used insulated underground piping to tap it into my existing system. Everything seems to work fine, except I am getting unwanted heat in some rooms even though the thermostats are not calling for heat (hydronic convection). The rooms will be up to 10 degrees higher than the thermostat is set for. I have flow check valves on all the lines. The heat is radiating up the return lines of my system. I plumbed my coal lines into the system and basically it is set up like a hotel hot water recirculating system where the pump is always running. This keeps the oil boiler temp up so it does not fire. How do I keep the heat from radiating up the return lines and making rooms hotter than they need to be?
hydronic convection
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Former Farmer
Minister of Fire
Zone valves controlled by thermostat.
They used to use large size piping and relied upon convection to circulate the water to the radiators. No circulating pumps.
They used to use large size piping and relied upon convection to circulate the water to the radiators. No circulating pumps.
velvetfoot
Minister of Fire
Are you sure it's coming in on the zone returns? There should be some check valves in there, no?
I have heat going up the supply zones, past the zone pumps and check valves if the boiler pump speed is set pretty high, when it should be going to the buffer tank; it seems to go away when at lower speed. I guess if I would've had zone valve instead of pumps it wouldn't happen.
I have heat going up the supply zones, past the zone pumps and check valves if the boiler pump speed is set pretty high, when it should be going to the buffer tank; it seems to go away when at lower speed. I guess if I would've had zone valve instead of pumps it wouldn't happen.
ewdudley
Minister of Fire
I have a peculiar situation where there is a common return pipe for two circuits and have seen return water from a more distant circuit rise up the return pipe of a closer radiator, then through a common supply pipe of another radiator on the same closer circuit, and then back down to the common return pipe of both circuits. And it is possible for hot water to rise up one side of a vertical return pipe, then through the a radiator, and then back down the other side of the vertical return pipe.
But it seems like if any of these peculiar things was going on you would have seen it before the the new boiler was tied in. It sounds more like the recirculating pump is tied in such that there is enough pressure on your flo-cheks to cause some unwanted parallel flow. Can you do a schematic sketch of the situation?
Yes, I'm sure the heat was coming in from the return zones. The supply side was cool to the touch. Return side was HOT. Here is a hand-drawn schematic of how my system is set up. I do have a Taco FlowCheck valve on the upstairs HWBB line with a Taco 007 pump, a Taco 007IFC pump on the rear downstairs line and the front downstairs line. A Taco FlowCheck valve on the hot water tank with a Taco 007 pump, and a Taco 007 on the coal lines. Im wondering if I put my coal line closest to the oil boiler instead of last in line, will it help? All the HWBB lines are 3/4" except the coal line, which is 1 1/4". Also, the coal line is approx 35' in basement and 155' underground, so im looking at 190' each way. That is why im doing the recirculation method, otherwise it would take quite a while for the hot water to reach inside, right? Is there a smarter way to run it? Would it be better to set coal line pump to only circulate when heat is called for? And if I do it that way, will my coal stoker boiler stay running or will it burn out without heat being called for?
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ewdudley
Minister of Fire
I'm scratching my head trying to see a way to complete a circuit through the upstairs. If there were more than one return connecton from the upstairs onto the return manifold then there would be a parallel circuit backwards up one return and then forwards back down the other, but that's not in the schematic.
One way to cure it would be to tee in the supply from the coal boiler into the supply line of the existing boiler and then tee the two returns together as well. Then maybe put an aquastat on the return line leaving the existing boiler that would activate the coal boiler pump.
The coal boiler controls are normally set up to run a minimum feed rate and if the boiler gets a little hot it will activate its circulator and will also provide a contact closure that can be used to dump heat somewhere.
One way to cure it would be to tee in the supply from the coal boiler into the supply line of the existing boiler and then tee the two returns together as well. Then maybe put an aquastat on the return line leaving the existing boiler that would activate the coal boiler pump.
The coal boiler controls are normally set up to run a minimum feed rate and if the boiler gets a little hot it will activate its circulator and will also provide a contact closure that can be used to dump heat somewhere.
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The coal circulator pump is NOT hooked to the "brain box" but is wired through a flip switch so it is always on.
ewdudley
Minister of Fire
Thanks for the second diagram, it's clearer but doesn't contradict the earlier sketch and description.
I can't explain why you're getting heat going up the return lines unless it's a case of hot water going up one side of the pipe and cool water falling falling back down the other side of the same pipe, but with baseboard that seems pretty far-fetched.
One thing you could try would be to take the 007 that is circulating from the coal boiler and turn it around to circulate the opposite direction, and then wire it to run when there is a call for heat or when you need to heat up the oil boiler to keep it from running.
I can't explain why you're getting heat going up the return lines unless it's a case of hot water going up one side of the pipe and cool water falling falling back down the other side of the same pipe, but with baseboard that seems pretty far-fetched.
One thing you could try would be to take the 007 that is circulating from the coal boiler and turn it around to circulate the opposite direction, and then wire it to run when there is a call for heat or when you need to heat up the oil boiler to keep it from running.
That is an idea. However, my "brain box" is only a 4 slot unit. I would have to replace with a 5 slot unit (or 6 in case I want to expand more). If I did that, would I just jump all my thermostat wires to the coal pump so it would turn on only when any of the other pumps call for heat?
ewdudley
Minister of Fire
And -- as I tried to sneak in as an edit to the previous post -- whenever the return side temperature of the oil boiler is low, so the coil boiler can back-fill the oil boiler to keep it hot enough not to run. You'd just need an aquastat on the return line coming out of the bottom of the oil boiler and OR that together with the combined call-for-heat signals from the four zones.
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velvetfoot
Minister of Fire
I'm not one of those previously mentioned geniuses, but if it was bothering you that much, how about a spring loaded check valve in A, B, C, and D? They're not that expensive.
so.....to sum it up.....if I purchased a Taco 6 unit zone control, I would reverse the coal lines for supply and return, then just jump the thermostat wire from pumps 1-4 to the coal thermostat wire so that when any of the zones call for heat, it will energize the coal pump as well? But if I did that, there would not be the hot coal supplied heat going thru the oil boiler. (however, I did remove the oil boiler jumper wire so it will not fire at all so it's not a big deal). This would by-pass the oil boiler completely, which is ok since I took the jumper wire out and it won't fire anyways. If I hook all the thermostat wires to the coal pump, would they backfeed a signal to the other pumps to start?
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ewdudley
Minister of Fire
What is your "brain-box", an SR504? And, BTW, what is the coal boiler and what controls does it have?
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It's a 504 zone control. The coal boiler is an Alternative Heating model with a hopper on top that gravity feeds. There are no pumps or overheat zones on it, other than the pump in the basement that is always circulating throughout the system. I think I will try the spring loaded check valves on my return lines and see how that goes. Prob the cheapest start. If it doesn't work, I guess I'll continue on with the other solutions mentioned by you guys. Somethings gotta work.
I installed the spring loaded check valves on the return lines. All problems fixed now. Thanks for everyones advice. I sincerely appreciate it.
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