Heat leaking from one zone to another

[mathfogie]

In a forced hot water heating system, how much heat should leak from one zone to
another? I live in a two story house in New England. When built, it had one zone
for each floor. There is a fireplace in the family room, and doors make it convenient
to isolate the family room and kitchen from the rest of the first floor. Since we
have a fire in the fireplace most evenings during the winter we had long considered
making the first floor two zones, for a total of three zones. A recent kitchen
remodeling project required some other plumbing changes, so we decided to add the
extra zone. When the entire remodeling project was done, we noticed the radiators
were hot in the first floor rooms of the no-fireplace zone, even when the thermostat
for that zone was turned off. Investigation revealed that the electrical contractor
had wired all the thermostats together; when any one called for heat, it caused all
three to call for heat. This problem was fixed, but the experience made me check the
system frequently for other problems. I found the no-fireplace zone radiators were
occasionally warm, even with the thermostat off. This happens most often early in
the morning. All zones are turned down overnight.

I don't know if this is normal or a result of the installation of the extra zone.
I don't recall ever feeling the radiators before.

Here is the configuration, in case it helps. The house is about 35 years old.
About 25 years ago I replaced the builder special by a Peerless boiler and
Beckett burner. Closest to the boiler is the pump for the no-fireplace zone.
It was installed with the replacement boiler & burner. Next is the pump for the
second floor zone. It is the original, huge, Red baron. Next is the new pump for
the kitchen and family room with the fireplace. All are properly on the return
side and the flow arrows all point down. All the thermostats are on the correct
side of the doors that divide the first floor into two zones, and now they are
connected to only the correct pump relay.

I can provide more detailed information if that would help.

Is this normal? If not, is it worth fixing? How?

Thanks much.

[Dana]

If the pumps do not have internal check valves or there are no check valves in series to block reverse flow, the pressure difference generated by a single pump pumping will cause a reverse flow on the other loop. The amount of that reverse flow depends on the capacity of the pump that's operating, and the pumping head of the in-active zones, and the drag of the inactive pumps. Since that reverse flow is injecting return water from the active zone into that radiation, it'll be warm, but not hot.

In some cases even with check valves there is enough convective force to get some flow, which is a function of the geometry & temp at he manifold.

BTW: An open hearth fireplace runs at about 7% efficiency. Tight glass doors and better damper & draft controls can roughly double that, but both produce gia-normous sooty-particulate output. An EPA-rated fireplace insert with a nice glass door for viewing can hit north of 75% efficiency (with or without a noisy blower for distributing the heat and boosting peak output). If you're heating even partially with wood, it's far better in terms of total fuel use and your local air quality (including your homes interior air quality) to use a wood-stove or wood burning insert. Burning wood in an open hearth is at least as expensive as heating with oil, but burning wood in an insert or woodstove is quite a bit cheaper, even at $300/cord (typical central MA pricing for decent split seasoned hardwood, delivered.)

[BadgerBoilerMN]

Ben Franklin knew this some time ago...

http://inventors.about.com/od/fstart...n_invent_2.htm

[mathfogie]

Thanks for the explanation. I had seen the check valves but did not realize what they were. If I thought about them at all I probably thought they were for reducing pressure or flow. The zone that heat is leaking into has a Taco 007F3R circulator. The Taco web site seems to have IFC as part of the model number for the pumps with an internal check valve, so I suppose the 007F3R does not have an internal check valve. I think I have found the problem. Just after the expansion tank, the supply side line splits.
The portion that goes to the second floor has a Taco 219 check valve. The remaining line goes through another Taco check valve and then splits for the two zones on the main floor. The new circulator is a Grundfos type 15-58 with a check valve. The Grundfos can pull water through the Taco and cause the warm radiator without the water going through a check valve. The Taco can't pull water through the Grundfos because of its internal valve, so I don't get hot dining room and warm kitchen radiators. I can even understand why the plumber might have done it. There is enough room to do it right, but not much room.

Now to figure out if it is worth the hassle and probable expense to get it fixed. If I end up doing it myself, replacing the circulator that does not have an internal check valve by an IFC circulator seems like the easiest job. That would even give me a spare for when the second floor circulator dies.

Thanks very much for resolving this mystery.