excessive chimney draft

Unknown

I am curious is this a gas or oil system? Is the boiler a designed oil or gas boiler? If it is a gas boiler there are some things I would suggest other than what has been posted here. If it has been converted to gas from coal or oil then I would suggest some different things. It is possible to control chimney draft in a number of different ways. Using stack dampers ( I assume you are talking about a barometric damper) can get you in trouble with some gas systems. It is also required to have a double swing barometric on gas equipment. If they are talking about a vent damper and it is a conversion burner then you can not use a vent damper on conversions. Post some more information and I will help you out. It is also important to know what the overfire draft is. One last question was this draft measured with the burner running at least 15 minutes? If it was on a cold chimney with no heat in the chimney that could be normal until the equipment fires and fills the chimney with products of combustion. THERMISTER is a thermostatic resister that changes resistance when temperature changes, what is it doing and what kind of control is it operating with? Or are we talking about some kind of fusible link designed to open on excessive temperature????? REALLY NEED MORE INFO!!!

[Deleted User]

ran across a steam boiler that had a chimney

draft of -.08''wc. What would cause excessive draft. would no cap on a masonry chimney do that? there is also something called a thermistor in the flue, whats that?

Dave_4

could be the height of the chimney causing excessive draft(nm)

Alan R. Mercurio

Gerry, Is there a barometric draft regulator installed? If yes you may want to confirm that it is sized properly and the hole in the flue pipe is completely cut out. This high draft condition could be caused by what's known as currential draft. Heck on a cold day it can even be caused by thermal draft if the barometric is not sized and adjusted correctly. I'm curious did you get an over fire draft? If so what was that?

There have been cases where more than on barometric needs to be installed.

Your friend in the industry,
Alan R. Mercurio

Steamhead

The Dead Men designed them like that

to pull combustion air thru the bed of coal in the original boiler. This takes a lot more effort than that needed for oil or gas. The now-excessive draft can pull all the heat out of the boiler during the off-cycle, forcing it to start from scratch on the next call for heat and resulting in excessive fuel consumption. This is especially true of atmospheric gas boilers.

The solution on a gas boiler is to install a stack damper. Both Noel Murdough of Slant/Fin and Glenn Stanton of Burnham agree that this is a good retrofit on their older gas boilers. As far as I know, no one is making stack dampers for oil boilers, so on an oil boiler you could use a burner with an inlet damper. It would be a good idea to check with the boiler and burner makers though, as I did with Noel and Glenn.

If the draft is excessive during operation, a larger draft regulator or hood may help. Again, it would be well to check with the boiler and draft equipment makers before doing this.

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[Deleted User]

no alan, there is not a barometric

installed..think that would help? its pulling so much i was thinking it may just suck the door open fully. never thought about possibly using two, tho. think that a barometric would slow things down a bit?

Alan R. Mercurio

Absolutely, as long as the system was not designed as a forced draft system then one should be installed. You'll see a difference once it's installed and at that point you may not need the second one that I was talking about. Those are extreme cases.

Good luck and please let us know how this turns out.

Your friend in the industry,
Alan R. Mercurio
www.oiltechtalk.com

Alan R. Mercurio

Dead Men Designs

Steamhead, Honestly I had never heard that but it makes perfect sense. I try my darndest to learn something new each day. Today you helped me accomplish that. Thanks man.

Your friend in the industry,
Alan R. Mercurio

Steamhead

I learn a lot here too

and am glad to give something back.

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John@Reliable

X-Draft

Jerry, Field controls has a great book (FREE) all about draft & thier products.Has drawings for proper set-ups and using more than one reg. Hope this helps

[Deleted User]

i just picked up a copy of the booklet

at a trade show last week and hadn't had a chance to look at it yet. so i dug it up, from amongs't the fifty other books. yes great diagrams. thank you much. it should help alot. ive used barometrics before, but always to get more draft from weak chimneys, which has always worked for me, but i never realized it would aid in controling high draft chimneys. well i never ran into a high draft chimney till now. what would i do without you guys? thanks

Paul Bock

I agree

Here in Portland where some of the older buildings have chimneys five or six stories tall, and were built for steam, it's not unusual to install barametric's even on pressure fired boilers.

Paul

Unknown

So Whats the Thermister For???

?????????

What control is wired to it????

Steve

Alan R. Mercurio

Steve, I would think it was installed with one or two concerns (or both) in mind. One would be the potential for the chimney to become plugged which would of course increase the temperature at the thermistor shutting the system down. The other may have been knowing excessive draft was present and flue temps could reach rather high temps that could potentially be dangerous therefore again the thermistor would shut the burner off.

My feeling would be this should be wired through the load side of the primary control (the orange wire in most cases) then back to the burner. just like a power venter or motorized flue damper.

Your friend in the industry,
Alan R. Mercurio

Mad Dog

ACTUALLY. Alan I hadn't until a few years ago.....

when the brilliant Jim Davis of National Comfort Institute showed us that in a seminar on CO....Mad Dog

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jim bannister

excessive draft

If this is an oil fired boiler, you should be more concerned with the over fire draft than the breech draft. Some boilers need a high breech draft to obtain the proper over fire draft. If you do feel the need to reduce the draft, a barametric is the way to go. For proper procedure with an oil fired appliance, let the unit warm up 10 to 15 minutes, check the oem's specs for over-fire draft and adjust accordingly.