boiler internal circulation

[mark123]

My wood oil combo (benjamin CC500) has 2 domestic coils about midway up of the water jacket. There is an external circ pump that circulates the boiler water between top and bottom. The manual says to set the pump to come on at 170. The problem is if the fire is going out, I run out of domestic hot water in little time, even though there is plenty of hot water in the jacket above the coils. I tried setting this pump down to 110 so basically the water remains uniform in temp throughout the boiler and I get much more domestic hot water. Is there a down side to doing this?

 

[Gooserider]

My wood oil combo (benjamin CC500) has 2 domestic coils about midway up of the water jacket. There is an external circ pump that circulates the boiler water between top and bottom.

I'm confused :-S does the pump circulate water between the two DHW coils, or does it circulate water through the boiler water jacket, as in a return water protection setup?

The manual says to set the pump to come on at 170. The problem is if the fire is going out, I run out of domestic hot water in little time, even though there is plenty of hot water in the jacket above the coils. I tried setting this pump down to 110 so basically the water remains uniform in temp throughout the boiler and I get much more domestic hot water. Is there a down side to doing this?

Assuming it's in the boiler water jacket, I'm not sure I'd set as low as 110 for the turn on temp, as it would seem to me like this might cause the boiler to take a lot longer to warm up, which might cause corrosion issues. However I don't see a big problem in having it turn on at a higher temperature, say 150 or so. The other thing that might be worth looking at is the differential temperature - or when the pump turns OFF. I can see why they might not want to turn the pump on until 170, and it sounds like your issue is more that it turns off sooner than you'd like. If you can get a control with a big enough differential, it should be possible to have the pump turn on at 170 as the boiler is heating, and then stay on until it cools back down to 110.

Another approach might be to look at getting a hot water storage tank and a mixing valve into the circuit - charge the tank to boiler max when you have a fire, and then live off the tank, mixing down appropriately, and then you don't have to worry about what the boiler is doing...

Gooserider

 

[mark123]

I also should have mentioned that the other bonus to having it set so low is that I get usable hot water much faster from start-up. If I light the boiler from room temp. I can take a shower after 15 min. If I have it set at 170 I have to wait much longer. I use the boiler all summer long for just this purpose. Wake up and light boiler with a few sticks of dry spruce, 15-20 minutes we take showers and then off to work. Same thing in the evening for laundry, dishes.... I didn't burn any oil last year because of this.