Circulator question

I'm hooking up a coal boiler and oil boiler in series. I was thinking about having a circulator running between the two of them to keep both boilers up to temp. The aquastat on the oil unit will have a low limit setting of around 125. This should keep the unit from ever kicking on because the low limit on the coal unit will be at 140. It should also kick the oil on if there is a fire out in the coal unit.
Is there a way to hook this circulator up to come on when the oil unit temp drops to 140 without using it's aquastat? My first thought was to use a timer on the pump to run it intermittently but I'd like to make the system more efficient by only turning on that pump when it needs to be on. Any suggestions?

billw wrote:I'm hooking up a coal boiler and oil boiler in series. I was thinking about having a circulator running between the two of them to keep both boilers up to temp. The aquastat on the oil unit will have a low limit setting of around 125. This should keep the unit from ever kicking on because the low limit on the coal unit will be at 140. It should also kick the oil on if there is a fire out in the coal unit.
Is there a way to hook this circulator up to come on when the oil unit temp drops to 140 without using it's aquastat? My first thought was to use a timer on the pump to run it intermittently but I'd like to make the system more efficient by only turning on that pump when it needs to be on. Any suggestions?

Your concerns are typical. However if your coal boiler is sized and operated properly, you don't need to worry about the oil boiler coming on if the coal fire goes out or drops below a certain temperature. Your coal boiler will kick ass and take names. No need for the oil. I'd just run the circulator constantly to keep the oil boiler up to temperature.

I'm not sure what you mean. You could attach another aquastat to a pipe, such as a L6006, that would start up or shut down a circulator.

If you only circulate from your coal boiler to an oil boiler you wouldn't have a problem like I did. My wood fire would go out over night. I'd start the fire again and 140 degree water would go from the wood boiler to the oil boiler......no problem at all. However, when the baseboard loop circulator would start, it would bring alot of cool water to the oil boiler and cause it to run for about 5 minutes. My goal was to not use oil at all, so I ended up installing a manual switch to disable the oil burner and yet allow all the other oil boiler controls to work. It works great. I used about 1/2 gallon of oil all last winter.

i have a keystoker kaa-2 plumbed in series with my oil burner and i dont have a circulator between the two units. i dont really think it is two nessacary to have a circulator between the two. you should not have too much of a temp differential. also hot water would convect to a cooler area. my coal runs about 160 for the summer and my oil burner temp is like 145-150 only about a 10 degree diffrence. so if i was you i would save on the elecrtic and not run a circulator 24-7. if you are so worried about loosing heat you can install an electric flue damper.

If you want to use the coal boiler in the summer for domestic hot water heat, you can use its domestic coil. If you don't want to do that, you can use an L6000C strap-on aquastat, mounted to your coil's hot water outlet on the oil boiler, which would start up a Taco 007 and circulate the coal boiler with the oil boiler. Unless you have an on/off switch to the oil burner motor, it may start up when the cool water slug hits the oil boiler's aquastat probe. This won't accomplish your plan of having the oil boiler kick in during an outfire at the coal boiler. You should have a L6006C at the coal boiler, mounted to it's outlet pipe, so you don't keep feeding coal during an outfire.

You can accomplish almost anything you want with a reverse-acting aquastat. Also known as a B aquastat. The L6006 will solve all your problems.

As far as electric usage, the Taco 007 is a great circulator, and it's the only one you need. It uses .71 amp. Doing the math, if the circulator ran 24/7, you would use 2000 watts a day X your kw rate; about 20 cents a day for PPL customers.

I'm probably making more of this than is necessary. The reason I'm thinking about keeping the idle oil burner water up to temp all the time is because my DHW coil is in it. I could put one in the EFM but I'm cheap, why buy what I already own. The second aquastat in the oil burner that controls the circulating pump sounds like a good, easy solution.

I have the same setup as you. No coil in the wood boiler and using the coil in the oil burner. A 6006 will work for you.