Barometric damper for shared flue?

At the advice of others in my posting about my EFM WCB-24 hand fired coal boiler with the leaking tankless hot water coil gasket leaking (which is now temporarily fixed) it sounds like it would be a good idea to install a barometric damper on my flue pipe to help control a more steady slow burn. As of now, if it's over 50 deg outside even with the draft control on the front of the ash door closed all the way the water will bounce between 195-205 all day while the aquastat occasionally kicks the circulation pump on to dump heat. Eventually the house will end up in the 80s without the thermostat ever calling for heat.

The gaskets around the load and ash doors look good so I don't think there are any leaks. There is a dayton blower on the front of the unit for a forced over-fire draft to get a wood fire started, but there is an adjustable metal damper that blocks 95% of the blower opening when its closed all the way.

So it sounds like the draft might just be too strong and is pulling too much fresh air in which is causing my sauna-like conditions in the house.

The chimney is shared between an old Columbia steel oil boiler and the WCB-24. I've attached a picture of the piping arrangement. Where would the best place to but the damper be? I know the best practice to to put on directly after each fuel source, but I don't think I have the room for that.

I've also attached a picture of what the flame looks like after the damper has been automatically closed for about 15 minutes once the water comes up to temp. It will eventually come down quite a bit more than this but still hot enough to constantly heat the water....

Any advice?

If you have no air leaks in the doors then try to turn down the high/low setting (150/160)for the boiler,that should stop the water from dumping and have plenty of boiler temp. By the way what is your boiler pressure looking like?
does the over fire blower turn on, if so turn it off.

Boiler pressure is about 16 lbs right now with everything up to temp.

So you're suggesting I turn down the draft control from 180 deg (there is no hysteresis adjustment) to about 150 degrees? Right now its set to just start opening the draft when the water dips under 180, but when it's up to 200 degrees like it was doing on Thursday when it was warm outside, the draft control shuts completely, so I'm not sure what lowering the control any further would do since the only difference will be even more slack in the lift chain.

The blower is shut off but I noticed the little cover to control the draft through it is really loose and I can feel quite a bit of air being sucked around it so I just temporary screwed a metal cover over it to completely block it off. I'm wondering if that had something to do with it...

It seems to be behaving much nicer today but with this cold wind my thermostat has been calling for heat more often.

I'll follow up later to report how completely blocking off that blow helped.

Thanks for all the tips!

W3DRK wrote:Right now its set to just start opening the draft when the water dips under 180, but when it's up to 200 degrees

I have mine set at 150/low and 160/high after the air draft shuts down the boiler temps continues to increase to 170 degrees and if theres more heat,it will stay in the boiler and not heating your house to 80 degrees.
I will let Rob explain how to adjust the aquastat,since he is far more experienced than me.

How hot was the boiler when you took that picture from the front?

(It looks like the flap held by the chain is open, if that is the case your thermostatic draft control is out of calibration)

I'd be tempted to remove that blower entirely and just use the manual control...when setup correctly they are very accurate.

As for the baro, that horizontal section of pipe before it joins the oil boiler piping looks like a good spot. There may have been a baro in that tee before the EFM was added.

Ok I understand what you guys are saying now.

I dumped the heat to get the water down to 160 and adjusted the draft control to have the draft closed with barely any slack in the chain at that temperature. Lets see how it does. Should I keep the aqua-stat for the dump zone at 200 degrees or lower it? Seems to me like 200 should be fine and gives me lots of headroom.

Rob, in that picture the water was still cold so the draft control had the door wide open. Once it came up to temp it closed like it should.

One of the benefits of keeping the boiler cooler is the domestic hot water won't be so dangerously hot!

I'll sit tight on the barometric damper for now and see if if lowering the boiler temperature helps with the runaway water temps.

Thanks!!

Baro damper would definitely help lower coal usage. Also, you really do need one on your oil boiler - a stripped flame and subsequent puffback from an oil burner puts coal backpuffs to shame - you don't want to have that happen, especially on a high GPH unit like that one likely is. In addition you REALLY lower the efficiency of an oil unit without a baro.

W3DRK wrote:One of the benefits of keeping the boiler cooler is the domestic hot water won't be so dangerously hot!

I would get a mixing valve on that DHW line right away to temper it down to about 130 degrees before someone gets scalded.

If your oil boiler was correctly installed, it would have had a baro on it. I suspect, as previously mentioned, that there was a baro on the tee in the flue pipe.

You only need one baro, it will maintain roughly the same draft to both boilers. I'd remove the ell entering the chimney thimble and replace it with a tee, and install the baro in the tee. Adjust the baro for about .05" or so. Either buy a manometer or hire someone who has one and set it on a fairly mild day with one of the boilers heated up.

*Disclaimer: I spent 20 odd winters working on oil and gas burners. It is not up to code and each appliance should have its own chimney flue.*

Having said that, find the stack draft specs for your coal burner, and if it is greater than .05", set the baro for that.

I've been thru some interesting situations with draft and dampers. I'll post it when I have time to write it out.

Ops