How low does your boiler temp drop when a zone is calling?

Hi, I was just wondering what is the lowest your boiler water temp drops to when a large zone kicks on? I know mine drops to between 140-150* this seems kinda low to me but this is my first season of burning coal. I have a tankless water heater in series with my boiler with a digital readout on it and when my garage zone kicks on it drops down to 47* F and the tankless kicks on to help bring the temp back up. This kind of defeats the purpose of doing away with the propane tankless water heater. Any feed back would be great

Does the boiler drop by 47 degrees or does it drop TO 47 degrees F?

Sounds like you need a bypass.

Someone w/ more experience will be along to get you up to speed.

Oops! I see RobR got you...you're in good hands.

Rob R. wrote:Does the boiler drop by 47 degrees or does it drop TO 47 degrees F?

It drops to 47 degrees F. I think it's Ferinheight not Celsius. it's the metric measurement. It reads 85 when the boiler is up to temp

47*C =117 degrees F, 87*C = 188* F, so your losing about 71Degrees Farenhiet with a larger zone(load) demand. The 47*C thats what it maintains while zone( load) is on, no lower?

wilder11354 wrote:47*C =117 degrees F, 87*C = 188* F, so your losing about 71Degrees Farenhiet with a larger zone(load) demand. The 47*C thats what it maintains while zone( load) is on, no lower?

It may drop lower if the tankless heater didn't kick on. I know one of the problems is that the 1200sq ft garage zone only kicks on 1-2 times a day so when it does call the temp of the water has dropped to 50* or lower. I don't know how to correct this prob. Any thoughts?

Ive seen mine drop down to 120 130, my operating temp is set at 160, all depends on current temp of water in the unit and how long circulator runs for

Did you turn down the mixing valve like we suggested before?

McGiever offered a very good answer. A bypass.

I installed an aquastat that shuts off my zone circulator when my boilers internal temperature falls to 145 degrees F. (63 C.) and does not permit it to start back up again until the boiler is recovering and has hit or exceeded 155 degrees F. (68 C.).

I also have a "differential pressure bypass valve" installed that functions somewhat as McGiever's solution intends, though not exactly (as that is not its primary function or intent).

Yes I followed the advice and I've got it turned down to about 116*. It still radiates heat from the slab for hours and I'm not sure what to do next.

lsayre wrote:McGiever offered a very good answer. A bypass.

I installed an aquastat that shuts off my zone circulator when my boilers internal temperature falls to 145 degrees F. (63 C.) and does not permit it to start back up again until the boiler is recovering and has hit or exceeded 155 degrees F. (68 C.).

I also have a "differential pressure bypass valve" installed that functions somewhat as McGiever's solution intends, though not exactly (as that is not its primary function or intent).

Thanks Isayre. That's a good idea. Does the aquastat cause the circ pump to constantly kick on and off? It seems like as soon as the cold return water came in it would kick the zone back off? I'm just trying to figure it all out not questioning your suggestion.

Coal boilers are not sports cars. They are more like freight trains. They take time to speed up and slow down.

It is very common to have the boiler temperature drop on startup of a large zone, especially if that zone is a cold one like a garage.

If your boiler has the typical honeywell aquastat, if the water temperature drops below the low setting, the pump will shut off until the boiler water temperature catches up. This will create even more load on any boiler in series. (depending on piping and pumping).

Better get that tankless set up in parallel with the coal boiler. Manually change it over or add controls for automatic change over.

EDit - Oops, forgot this is in the AHS forum. They do different things with their controls.

steamup wrote:Coal boilers are not sports cars. They are more like freight trains. They take time to speed up and slow down.

It is very common to have the boiler temperature drop on startup of a large zone, especially if that zone is a cold one like a garage.

If your boiler has the typical honeywell aquastat, if the water temperature drops below the low setting, the pump will shut off until the boiler water temperature catches up. This will create even more load on any boiler in series. (depending on piping and pumping).

Better get that tankless set up in parallel with the coal boiler. Manually change it over or add controls for automatic change over.

EDit - Oops, forgot this is in the AHS forum. They do different things with their controls.

Thanks for the info Steam Up. I've got so much to learn.

chevymatt wrote:Thanks Isayre. That's a good idea. Does the aquastat cause the circ pump to constantly kick on and off? It seems like as soon as the cold return water came in it would kick the zone back off? I'm just trying to figure it all out not questioning your suggestion.

I've only noticed the circulator stop due to my boiler being at 145 degrees a scant few times. It mainly seems to happen when the boiler fan has not come on for many hours and the boiler is therefore "sleepy" (for lack of better terminology here). or just as for your case, if my cold garage zone loop has a heat call, or lastly if I have multiple of my zones all begin their call for heat at just about the exact same time. By the time the boiler has recovered to 155 it is on an upward "freight train" roll and still rapidly gaining heat (the fan is still running) so I have never seen it kick right back out again when the pump is restarted. Plus by that time the cold water is pretty much out of the offending zone loop (having been replaced by at least 145 degree water), and when the pump comes back on its probably still at least 120 degrees within the loop so there is not a second dip in temperature that can bring it back down to 145 degrees over and over again.

My boiler fan comes on at 170 degrees F. and turns off at 180 degrees F.

chevymatt wrote:Yes I followed the advice and I've got it turned down to about 116*. It still radiates heat from the slab for hours and I'm not sure what to do next.

Does the garage call for heat come from a standard 24 volt wall thermostat?

If so, where is it physically located in the garage?...not on an outside wall?

The slab is obviously being over saturated w/ heat, since it radiates for hours.
This over saturation is also causing the long time period between heat cycles and therefore is causes the big temp. drop when all cold water in that loop is sent back to the boiler.

The placement of the t'stat will determine how the system will respond for both the ON call and the OFF call for heat in any space.

Maybe someone else w/ more radiant experience could recommend a "slab thermostat"