Carlin gas conversion on Weil cast iron boiler - draft too high

weekendguy

I have a Weil McLain WGO-6 boiler that was converted 7 years ago to propane with a Carlin EZ-GAS burner. I decided to check the draft the other day when it was really cold since the tall chimney (40' from the breech) has caused draft issues in the past (while on oil). The specs call for -.02 and I can't get any lower than 0 holding the damper wide open. The flue is 7" round. Combustion air comes from outside. It seems to me that I need to either increase damper flow to satisfy the chimney without pulling so hard through the boiler, or restrict the draft somewhat between the boiler and the damper. If I am on the right track, would it make sense to upgrade the 7" Field MG1 to 8". It's mounted in bullhead tee which is only 7" all around. so I think I would need to replace the flue pipe from the damper to the chimney with the larger size. Something like: boiler-> 7" pipe-> 7-to-8-reducer-> new 8" bullhead tee-> 8" pipe to the chimney. Does this make sense or is there a better approach?

icesailor

Some of we soot sucking guys, when presented with the problem of the draft being too high in the stack/chimney, have found that the addition of a second damper fills the need.

weekendguy

@icesailor - thank you for that suggestion - but I don't think I can fit another damper on the short run of pipe that is not behind copper runs. If I got an 8" Field damper with a collar, can I fit that collar to the 7" pipe or is the radius too far off?

Steamhead

We routinely use a barometric one size larger than the smoke pipe when connecting to an older chimney that was designed for a coal-fired boiler. These chimneys can pull so much draft when it gets extremely cold that they overwhelm a normal barometric.

Post a pic of your installation- let's see what you have.

weekendguy

Now I'm confused. Stand by for pictures.

weekendguy

Here are three pics from different angles - sorry about the cellphone quality. Yes, @Hatterasguy, I stand corrected. I have insufficient draft. Reading the gauge backwards. The next time the boiler kicks on I will check again - maybe I can tweak the weights and be done!

weekendguy

Thank you. Looks like some success here, . See pic of gauge - this is reading -.02, correct? That zero to the left had me confused. Also, the damper has weights inside the door and has the chain and washer arrangement on the right side (see pic). I backed off the upper-inner weight and that got me to -.01, then had to add 2 washers to get to -.02. Is this right? Seems unnecessary to have two different ways to balance the damper unless I am misunderstanding its design.

weekendguy

@Hatterasguy, and others - thank you very much. I'm in good shape for now. It's 35F outside but in a few days it will be in the low teens and I'll give it one more look. I see now that the upper weight was added to this MG1 - possibly to induce more draft. Best to all.

Larry_52

You need to measure over fire pressure. You should adjust based on over fire, if you boiler fireside is clean. You do not adjust the weight on the controller you add or remove weights from the chain weight. You are missing the screw in the chain weight arm for horizontal or vertical position. Make sure that sheet metal screw in the flue does not interfere with swing. Make sure the damper is level.

Hard to tell by pics but I think you are also missing the angled inserts that the swing gate rests on.

BobC

Watch out for that sheet metal screw, I had to grind mine down by a good 1/8".

Bob

weekendguy

Thank you for your comments. Damper is level - I actually removed the screw and replaced it with a rivet some time ago because it was scraping the gate. I'll give it another look.

icesailor

Your question was posted as if the problem was excessive draft and how to correct it.


If the inside weight is properly set, you MUST tighten the square head stove nut against the back of the damper to keep the adjustment. otherwise, the weight can fall out and be lost. There's more to adjusting a Field MC damper than what you have done. You need to adjust the inside weight too. The first photo you shoe with the draft gauge showing zero and the probe out of the flue pipe shows draft because the gate is open. If you have a 40' chimney that was used for an oil flue, it might have issues. That's why it should have had a liner when the fuel was switched from oil to gas.

Its often a harder problem with draft over the fire. Significant positive draft over a fire is a bigger issue. You have to look at what the burner and boiler manufacturers spec out, and in a conversion, decide how to apply it. Not simple.

captainco

On gas barometric you never adjust the weight on the damper. This could cause the damper to to swing open and stay there. That center weight is adjusted to a sensitivity of .005".

icesailor

The nut still needs to be tight when you are done.

Either way, adjusting gas or oil boilers for proper combustion efficiencies isn't something you can read on the Internets or watch on the Youse Tubes.

Its like if that damper was a "RC" for oil. Is that a horizontal (less than 45 degrees from the vertical) or a vertical flue? (More than 45 degrees from the Horizontal) It makes a difference on which side of center the weight goes and it is marked on the damper gate.

Larry_52

@icesailor.

The mg field control damper is a double swing and the point that some are trying to make is it is set from the factory to be balanced in level position. To adjust the damper you add weights to the chain. In fact it is written right on the sticker that is right by the damper weights. So hopefully that lock nut is right where the weight used to be and you can put the weight back where it is supposed to be

Larry_52

weekendguy said:

Thank you for your comments. Damper is level - I actually removed the screw and replaced it with a rivet some time ago because it was scraping the gate. I'll give it another look.

The screw that is missing is on the lever arm that the chain pulls on. It is a two position screw you put the screw in the hole that is meant for mounting position. Suggest you go to the website for field control and read the installation manual of the mg series damper.

icesailor

In the photo, there is a bolt through the inside weight. There is a square head nut that is supposed to lock it in place. The nut is loose in the photo. It shouldn't be loose.

I also consider that people shouldn't be futzing with gas burner combustion settings that aren't properly trained or qualified to do so.

IMO, there are instances of people coming here with issues that are asking for help with that are far beyond the ability of an Internet web site to resolve without sliding down a slippery slope to danger. This is one of them.

A lot of us who are well experienced with oil burning equipment deal with this issue on a regular basis. You can't explain experience. How we got around a problem like this requires experience. People are coming here with ideas that just go against common sense. They got them somewhere. Help out with some of these fallacies and you promote them by giving them legitimacy. You have a draft problem, MAYBE. What do you do?

Tell the customer they need a new 40' chimney?

Or, you use your experience and skill to make the proper adjustments to make the appliance as efficient as possible. Using the skills and the tools you have learned and developed over time.

Without seeing all the I/O for the equipment, that draft may be as close as you will ever get on a day with no wind. Come back on a day when it is blowing 10 to 15 and gusting to 22. See what the draft is. And falls into the acceptable range of adjustments.
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When I think of bad draft, I think of the burner coming on, the boiler starts shaking, and if the draft control isn't properly screwed in, the shaking blows the damper out of the stack and my CO alarm will go off in a few.

weekendguy

Thank you for your comments. As was mentioned a few posts ago, I actually had too low overfire draft (my error originally saying too high) which has been corrected by adjusting the swing gate weights. Also, the weight on inside/top of the gate was not originally part of the unit - it was added for extra weight. I have not touched the weight on outside/front of the gate. @captainco I will see if I can get the same balance by removing the added front weight and adjusting the chain weights - I spoke to the installer last night who recalled having a problem getting enough draft when installing and that's probably why that weight was added. I appreciate all the comments. I'll write another post if I have any further questions.

Larry_52

Ok now this makes sense. The weight on the inside of the flue is original and goes where the outside weight is ( looking at pics). The weight is set to perfectly balance the damper as mentioned above. Remove the outside weight and balance the damper with the removed inside weight moved to where the removed outside is. Again the damper needs to be perfectly level. If you cannot attain proper draft with weights on chain then just add another damper, although I don't think you will need to go there. If you open the damper all the way what do you read in the flue?

Larry_52

What size damper is this? I would ask the installer exactly what he did with the weights to make sure what was where.

icesailor

I'd buy a new untouched and never screwed up damper. No one will ever get it back to what the factory started it with.

Its cheaper to get a new damper and install it than to have someone continuously futz with it to get the old one right. And maybe never get it right.

weekendguy

Actually I was able to remove the extra added weight which restored the damper to its original design and I balanced the damper with the chain and washers. I watched it for about 30 minutes of running and it averaged just under -.02. The damper is otherwise fine and is only a few years old. So the draft problem is solved - thank you all for your helpful ideas!