Coal boiler zoning, thermostat control

Coal boiler zoning, thermostat control

PostBy: crmoores On: Sat Sep 02, 2006 9:19 pm

This is a 2-part question, please, appreciate any help you can provide -

I had a Keystoker K6 installed late last winter, and it is wired into my 3 existing zone thermostats rather than on a separate thermostat. This allows for optimum zone heat control, as with a regular gas boiler. The problem is the gas boiler still wants to keep the water to the temperature on the gas boiler aquastat. This isn't a savings, obviously. I turned the BTU's down to 150 on the gas boiler aquastat and it still wanted to fire, not sure why. This is an old gas boiler.

Question 1 -
The gas boiler has a "main" gas line and a separate gas line to the pilot.
So I'm wondering as the season approaches if I can simply turn off this main gas line to the gas boiler (as I do in the summer) to keep the gas boiler from wanting to heat the water and take advantage of having the 3 zone heat control?

Question 2 -
I know it is typical to have the coal boiler on a separate thermostat that is set slightly higher than the gas boiler thermostat so if the coal fire goes out the gas boiler will come on.
How often do coal boilers go out or shut down? If there's a power loss the gas boiler will be out of commission as well, won't it?
Is the current installation using the existing zone thermostats ill-advised for any other reasons? I don't plan on leaving the coal boiler on when away from home for more than a day or two, and will turn on the gas boiler in those cases.

Thank you for your comments and your help. This will be my first year using coal and this site has already been invaluable. I know I will learn much more here as the season begins.
Ron :lol:

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PostBy: JK Hampshire On: Thu Jan 25, 2007 11:12 pm


I am running the same boiler for 3 years now and am very pleased, it has halved my winter heating costs.

You want this connected to run with all your existing thermostats and zones just like the gas boiler and aparently that is how it is connected now, that is good.

What you need to do to correct your problem of the gas boiler firing is this, install an additional aquastat on the Keystoker to the tapping on the flue end near the top (near the domestic hot water coil you will find a threaded tap with a plug in it), this thermostat needs to OPEN ON THE TEMPERATURE RISE, then you need to run a thermostat wire from this to the aquastat or firing circuit on the gas boiler, disconnect one wire on the gas boiler and wire nut it to one wire from the new aquastat, then connect the other wire from the new aquastat to where you disconnected the wire on the gas boiler. Basically you are adding a switch to the firing circuit of the gas boiler.

Once you have the aquastat installed and wired to the firing cirucit of the gas boiler, set the new aquastat for 130 to 140 degrees F. What this will do is prevent the gas boiler from firing as long as the coal boiler is hot but will let everything function just like the gas boiler alone did before. If the coal boiler goes out for any reason it will cool down to below 130 or 140 causing the aquastat to CLOSE the circuit to the gas boiler allowing it to fire normally.

I originally had a HS Tarm wood boiler on my system and tryed setting the gas boiler aquastat lower to keep it from firing, it did work to a point but when the wood was out and the gas finally fired it was to cold and the system woouldnt heat the house properly, thats when I installed the aquastat as described above and then did the same thing for the Keystoker. Mine works like a charm and I dont use any gas till I have to shut the coal off inlate spring for the summer.

If you have any other questions drop me an e-mail, if you want I will give you my phone number.


JK Hampshire

coal boiler zoning...

PostBy: keyman512us On: Mon Feb 05, 2007 7:31 am

I was reading your post. The question I have for you is what type of aquastat? Single or triple acting aquastat? Turning the temperature setting down on the aquastat is not the answer. You have to understand how an aquastat trully works. If it is a triple acting aquastat once the thermostat calls for heat, it is going to fire unless the system temperature is above the high limit setting. Does the aquastat have a "ZC" or "ZR" terminal. Does your main boiler have a T-T terminal configuration on the ignition control? You have a few options...but need to know a little more info. Depending on what controls you already have, you could add a simple "inhibit" circuit to the system with a relay and a thermostat for under $100 (depending on how mechanically inclined you are). If interested contact me for more info.