Hydronic baseboard zone question ...

fsteyer · Feb 3, 2006

Hi -
on one of my jobs I noticed that on a 3 zone hydronic system with individual circ pumps all zones stay warm when shut off by the stat. Even if only one pump is on all zones seem to be fed. When I look at the setup I only see shutoff valves at the pumps but no check valves. Is the lack of check valves making the hot water circulate even without the circ pump(s) on?
While I'm at it one more question please ... is it a code requirement that all electrical feeding circ pumps burners, etc are BX cable?

Thanks ...

Plumber1 · Feb 3, 2006

Hot water rises and cold water falls. Systems like you describe used to have a flow control valve on the feed , or top outlet of the boiler. They can be manually opened to stay open and if not manually opened the flow control valve acted as a check valve. It was weighted enough to stay closed and not allow the gravity circulation. But would open when the circulater began to run. So you must be getting gravity circulation .

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Cpeters · Feb 4, 2006

I was thinking of replacing my boiler

I was going to replace my boiler. I have two zones with two flow controls.
Are the worth the extra cost? I was told that if you manually open them they can heat the house via gravity. With the electronic ignitions the idea of heating your house if the power goes out is lost. How necessary are they? Thanks.

fsteyer · Feb 4, 2006

thanks on the gravity feed issue. If I understand it correctly, then a flow check valve wouldn't solve anything because gravity feed could work in either direction, no? The only part stopping it is a zone valve or am I wrong?

Thanks

Bob NH · Feb 4, 2006

"on one of my jobs I noticed that on a 3 zone hydronic system with individual circ pumps all zones stay warm when shut off by the stat. Even if only one pump is on all zones seem to be fed. When I look at the setup I only see shutoff valves at the pumps but no check valves. Is the lack of check valves making the hot water circulate even without the circ pump(s) on?"

If there are no check valves (sometimes there is a check valve in the pump), then when the pump of one circuit is pumping it will cause some reverse flow in the other circuits, bypassing the boiler heat exchanger. The reverse flow is usually small because the flow resistance of the circuit is greater than the flow resistance of the boiler heat exchanger. However, the diminished flow through the heat exchanger reduces the capacity of the heat exchanger and reduces the ability of the system to deliver heat to the intended zone.

hj · Feb 4, 2006

pump

A pump pushes, or pulls, water through its connected circuit, then through the boiler, in continuous loop. There is nothing that can induce its flow through and adjacent loot, since both sides of that loop are at the same potential pressure. Unless the pump has a high resistance between it and the boiler, and there is also a major resistance between the boiler and the feed manifold, which would indicate a faulty installation.

Bob NH · Feb 4, 2006

"There is nothing that can induce its flow through and adjacent loop, since both sides of that loop are at the same potential pressure."

Draw a picture of three loops, each with a pump, without check valves, with one end of each loop manifolded to the return of the boiler and the other end of each loop manifolded to the outlet of the boiler. It doesn't matter if the pumps are at the outlet or the return of the boiler.

When a pump is running there is always a small pressure drop through the boiler, probably too small to measure with typical gauges. That pressure drop creates a pressure differential for each of the non-pumping loops, and that is what causes backflow in those loops.

When one pump is running, the non-pumping loops each constitute a bypass circuit around the boiler. The flow through the boiler is in the intended direction and the flow through the non-pumping circuits is in the reverse direction.

fsteyer · Feb 4, 2006

thanks .. so how do you stop that flow? a zone valve?

Bob NH · Feb 4, 2006

Since you have a pump in each loop, you need only a check valve to stop the reverse flow. Check the model number of the pump to see if it has a check valve. Some do.

Use a swing check because the head supplied by a circulator pump is very low.

Plumber1 · Feb 4, 2006

zones

Seems to me that your zone valves that are off, would not allow the water to circulate gravity or allow flow when only zone is calling for heat.
Do the thermostats operate the zone valves and when they are opened it calls for the pump to run?

fsteyer · Feb 5, 2006

thanks - ... there are no zone valves right now, only 3 circ pumps. Even with all pumps off I get flow through the upstairs loop.
Could you please explain to me why a (one directional) check valve would stop gravity feed since it seems that gravity feed would then just reverse its direction of flow ( with the direction of the check valve) and still exist. Or am I wrong here?
A zone valve paralleled on the stat with the circ pump would do the trick though, or am I wrong?

Thanks again guys

Jimmym · Feb 6, 2006

fsteyer said:
Hi -
on one of my jobs I noticed that on a 3 zone hydronic system with individual circ pumps all zones stay warm when shut off by the stat. Even if only one pump is on all zones seem to be fed. When I look at the setup I only see shutoff valves at the pumps but no check valves. Is the lack of check valves making the hot water circulate even without the circ pump(s) on?
While I'm at it one more question please ... is it a code requirement that all electrical feeding circ pumps burners, etc are BX cable?

Thanks ...

Is the system a primay/secondary loop configuration? (1 boiler circ pump, plus one pump dor each zone). Or is it just 3 zones pumped into the boiler without a primary loop?

You need a flow check (not swing check) at both connections of the zone loop to the primary loop. There's (possibly) convective flow through the loop itself if you have no checks. Also, if you have only one check, convective flow inside the pipe without the check.
Check out www.pmmag.com. They have TONS of hydronic information. Specifically John Siegenthaler. This guy is a hydronic god.

Plumber1 · Feb 6, 2006

heat

I'm no heating expert, and Ive seen a lot of systems, but yours is not one.
Who did the engineering on that system? Never heard of thermostats just starting circulators with no flow control and no zone valves. What fore , just to save a couple a bucks on an important part of the house?

With your set-up, seems like a flow control valve would solve the gravity circulation.

Hydronic baseboard zone question ...

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