condensation problem

[Wade]

does this sound reasonable? Starting heating up my 3000 gallon boiler, after 6 hours temp had risen from well water temp 6'C to about 40'C. Shut it down for the night,came back next morning fired again. After 1 hour I started to get moisture out of my secondary chamber. Shut it down, and after some inspection I found that my Heat exchanger in the tank had enough water in the bottom of it, it was able to run out of the stove. After a moment of despair and sitting in a snowbank, its cold up here now,getting to -13'C . I drained all 3000 gallons of water from the tank,can you say lake, and climbed into the tank for an inspection. Could not find any problem, checked some gaskets and tightened some bolts.Could not find the leak. Put everything back together and filled her up again. Fired the boiler again and after the same amount of time, water from the front of the stove! I was about to push the unit into the bush with my dads cat, wasn't feeling happy at this moment, when he brought up the pipe plugs. He wanted to do a compression test on the heat exchanger. It held at 40 psi for a couple hours so it wasn't the heat exchanger.
So i came to the conclusion it had to be condensation. We drilled a hole in the bottom of the secondary chamber and any water that came in, drained out. We fired again and water started to drip out at a fairly good rate. The exhaust was still clear, no sign of anything. Then at about hour 10 steam started to pour out of the exhaust. Shut her down again, thinking that the water had reached the flame path, not good. Everything was normal though. Temp of tank had reached 70'C. Fired it for the rest of the day, and shut it down for night. In the morning we did a complete inspection, and the heat exchanger was almost dry.
So my conclusion is that until the water in the tank reached a certain temp the water vapor in the exhaust never made it out.Once the steam started exiting the chimney everything worked.
Does this sound reasonable, or will i be making another skating rink for the kids with 3000 gallons of hot water!!

 

[Eric Johnson]

What kind of boiler is it?

 

[Wade]

Homemade job, we call the Gale Force. I designed it for all the guys around here that don't want to mess with switches and fancy tech but still want to save on wood. Performs very well except for the heat exchanger may be taking off too much of the heat, hence the condensation.

 

[DaveBP]

Wade, do you have any means of assuring a minimum temperature on the water returning to the boiler. Most, I think, are using some sort of thermostatic mixing valve on the return line. The lowest rated ones I know of start to open at 140F. Is your water coming into the boiler at least that high?

 

[Wade]

No, do not know what the temp is. We turned on the 2500 sqf slab with in-floor heat. When the water returns from there to the boiler its lucky to be just above freezing, until the slab heats up.After that the slab calls for little heat and returning temps are quit high.
Another thought, my heat exchanger is on the bottom of the tank. The tank is 7' tall by 12' long, there is quite a temp difference.The top could be 90'C and the bottom with the return line down to 40'C. Could this be a problem and is there a way to overcome this layering effect?

 

[slowzuki]

What's happening for you is normal. You don't see steam early on because you are condensing all the water out. Best you can do is keep draining the water. Once the tank is up to temp you shouldn't have as much trouble. If you let the tank get down really cold again you'll get that mess of water again.