Vent damper

neurosteam

Hello experts,

Do I need to add a flue damper to my residential Weil McLain steam boiler to improve effieceincy and operation.

ChrisJ

neurosteam said:

Hello experts,

Do I need to add a flue damper to my residential Weil McLain steam boiler to improve effieceincy and operation.

What kind?
Oil? Gas?

HVACNUT

> @ChrisJ said:
> (Quote)
> What kind?
> Oil? Gas?

Barometric?
Mechanical?

neurosteam

The boiler is fueled with gas.

neurosteam

I am not sure if I need a damper or not and what kind mechanical or not.
It was recommended by local non steam contractor.

ChrisJ

neurosteam said:

I am not sure if I need a damper or not and what kind mechanical or not.
It was recommended by local non steam contractor.

I assume the appliance has a drafthood? Or was it converted from oil to gas?

Can you post some pictures?
How's the chimney situation? Approx height, diameter, location etc.

neurosteam

Chimney right behind the boiler. Picture attached.

neilc

it took me a moment to realize your picture was sideways,
I got scared,

if you're looking to eake out additional efficiency, then yes, a powered vent damper will stop some draw and cooling of the boiler, and the basement.
don't let them sell you a barometric damper, not your application.

Efficiency wise,
your guy has tuned the burner already ?
and you trust him / her ?

neurosteam

My guy is not an expert unfortunately. He tries and I try by increasing my knowledge through reading thanks to this forum. Tuning the burner? The burners get cleaned that’s it. He does not tune it.

HVACNUT

You wouldn't save much by adding a mechanical flue damper. There is the large dilution air box at the back. Open underneath.

neilc

HVACNUT said:

You wouldn't save much by adding a mechanical flue damper. There is the large dilution air box at the back. Open underneath.

I almost hit the disagree button , , ,
sure, there is a large dilution box there,
and to close off that continuous draft, when the boiler isn't firing, does help keep the boiler that little bit warmer, along with not continuously drawing air out of the basement,
the boiler heat sits in the basement.
I'm a building envelope Nazi,
close all the holes.
I'm pretty sure any new boiler, or furnace, that is still atmospheric, come with the stack damper, to increase or provide this efficiency.

and yeah, the gas burner needs to be tuned just like any other burner,
OP, you should find a tech for this.

nicholas bonham-carter

Where does the combustion air come from in the basement?—NBC

neurosteam

Basement combustion Air? Can you clarify more please.

mikeg2015

Only problem is the dampers aren’t cheap. Savings is probably 3% at most. And much of the saved heat goes into the basement which only indirectly heats the occupied parts of the house.

That being said, even in summer I’ve witnessed a pretty strong draft when the sun hits the exposed part of the chimney. Which oddly would increase reverse stack effect where hot humid air leaks in from up high and cool conditioned air leaks out through the basement. It’s one of the reasons basement are so cool in summer. All the cool air is falling and leaks out the sill plate.

As far as I’m aware, All atmospheric boilers have the flue damper after the draft hood so there some heat rolling out after shutdown.

ChrisJ

mikeg2015 said:

Only problem is the dampers aren’t cheap. Savings is probably 3% at most. And much of the saved heat goes into the basement which only indirectly heats the occupied parts of the house.



That being said, even in summer I’ve witnessed a pretty strong draft when the sun hits the exposed part of the chimney. Which oddly would increase reverse stack effect where hot humid air leaks in from up high and cool conditioned air leaks out through the basement. It’s one of the reasons basement are so cool in summer. All the cool air is falling and leaks out the sill plate.



As far as I’m aware, All atmospheric boilers have the flue damper after the draft hood so there some heat rolling out after shutdown.

What about the fact the chimney stops sucking heat out of the basement in between cycles?

I'm betting most of the heat lost into a basement ends up in the livingspace as well.

Motorapido

I have smart home temperature/humidity sensors throughout my house, including the main basement and boiler room. I saw a significant temperature increase in my basement and shorter time-to-produce-steam when I replaced my formerly broken automatic damper (meaning that the damper was always open before I replaced it) on my atmospheric draft gas fired steam boiler. Sure, it adds a control mechanism that will eventually fail, but it's keeping the rush of cold chimney air out of my basement and allowing my boiler to produce steam faster. I vote for you to add the damper. I fully insulated my wet returns, too, both to decrease the production of carbonic acid as the condensate cools and also to retain the condensate heat so the boiler can produce steam faster. Cheap investment in efficiency.

mikeg2015

My roughy math says it saves around $50 per year for natural gas. 40f average temp rise, 50cfm, $1/therm, 85% boiler duty cycle.

PMJ

This one isn't sort of maybe or even close.

Get the damper. Easily worth every penny.

That wide open flue exhausts air you already paid to heat every minute your burner is off.

Even if you supply outside combustion air that isn't the biggest thing. Time to steam from burner start is dramatically affected by this and as far as I can tell completely overlooked around here. The cooling effect on that boiler between cycles will add minutes to the time to steam on every firing. These minutes of burn time that don't need to be there add up. Outside combustion air without the damper will make this even worse as it would cool the boiler even faster without a damper.

Think about it. These are all minutes you are firing the burner and not making steam. You are replacing heat that went up the flue in order to get the boiler back warm enough to make steam again. That is one loss that doesn't need to happen at all.

Time to steam is a really big deal with regard to efficiency. Those who don't appreciate that won't appreciate what vacuum can do either which drops time to steam down a lot further yet.

Hap_Hazzard

My boiler didn't have a vent damper, and it worked that way for years, but I added one, and my basement stays a lot warmer between cycles now.

Originally, none of the piping in my basement had insulation, so the basement would get really hot when the boiler was on, but the hot air could go up the chimney with very little trouble, and the temperature swings were pretty extreme. Now, with the pipes insulated and the vent damper installed, it's warm all the time.

Jamie Hall

Vent dampers probably aren't a bad idea. Will they save the cost of investment? Hard to say.

One thought, though, which certainly doesn't apply to everyone: the mean time between failures on a vent damper has been, in my experience, much shorter than any other control or device, at least on the systems I've been exposed to -- and they fail closed. This not an issue when the structure is occupied and there is someone qualified to go and manually open the damper when it fails. When it is a structure where this isn't the case, however, it would be wise to have a remote alarm capability to tell the responsible person that the heat is off.

Just based on experience -- and your mileage may vary -- I currently care for 3 historic properties, and have for a number of years. In that time I've had one total failure of a burner control (welded contacts on a relay) and no failures on any other device -- except an average of 3 failures per structure per year on vent dampers (which have all been removed for that reason).

PMJ

Jamie Hall said:

Vent dampers probably aren't a bad idea. Will they save the cost of investment? Hard to say.

One thought, though, which certainly doesn't apply to everyone: the mean time between failures on a vent damper has been, in my experience, much shorter than any other control or device, at least on the systems I've been exposed to -- and they fail closed. This not an issue when the structure is occupied and there is someone qualified to go and manually open the damper when it fails. When it is a structure where this isn't the case, however, it would be wise to have a remote alarm capability to tell the responsible person that the heat is off.

Just based on experience -- and your mileage may vary -- I currently care for 3 historic properties, and have for a number of years. In that time I've had one total failure of a burner control (welded contacts on a relay) and no failures on any other device -- except an average of 3 failures per structure per year on vent dampers (which have all been removed for that reason).

Agreed, your mileage may vary.

One tip - install them as far from the boiler as possible. I installed mine 23 years ago on a 10 inch flue. Still haven't had issue #1 with it and I run many more cycles than most.

And as far as investment return the conventional wisdom will be that this is a marginal call. I think it is a clear winner on efficiency and mostly because of the time to steam issue. It is not just the already heated air leaving that you have to account for. It is the additional heat concentrated in the boiler that leaving air picked up on the way out. Straight up dead loss that is because it didn't need to happen at all. There will be additional minutes every burn to make up for it.

ChrisJ

PMJ said:

Jamie Hall said:

Vent dampers probably aren't a bad idea. Will they save the cost of investment? Hard to say.

One thought, though, which certainly doesn't apply to everyone: the mean time between failures on a vent damper has been, in my experience, much shorter than any other control or device, at least on the systems I've been exposed to -- and they fail closed. This not an issue when the structure is occupied and there is someone qualified to go and manually open the damper when it fails. When it is a structure where this isn't the case, however, it would be wise to have a remote alarm capability to tell the responsible person that the heat is off.

Just based on experience -- and your mileage may vary -- I currently care for 3 historic properties, and have for a number of years. In that time I've had one total failure of a burner control (welded contacts on a relay) and no failures on any other device -- except an average of 3 failures per structure per year on vent dampers (which have all been removed for that reason).

Agreed, your mileage may vary.

One tip - install them as far from the boiler as possible. I installed mine 23 years ago on a 10 inch flue. Still haven't had issue #1 with it and I run many more cycles than most.

And as far as investment return the conventional wisdom will be that this is a marginal call. I think it is a clear winner on efficiency and mostly because of the time to steam issue. It is not just the already heated air leaving that you have to account for. It is the additional heat concentrated in the boiler that leaving air picked up on the way out. Straight up dead loss that is because it didn't need to happen at all. There will be additional minutes every burn to make up for it.

The manufacturers like to set them up to slowly bake the motor/gear box directly over a drafthood for some reason.

Mine is mounted up away from the boiler now but I had to modify and extend the cable.

Hap_Hazzard

PMJ said:

One tip - install them as far from the boiler as possible.

ChrisJ said:

The manufacturers like to set them up to slowly bake the motor/gear box directly over a drafthood for some reason.

DOH!

I didn't even think of that. When I installed mine I just did it the way they showed in all the pictures, not even thinking that it could just as easily have been mounted at the top of the pipe as the bottom, or thinking about how heat might damage the motor. What a dork I am.

PMJ

Hap_Hazzard said:

PMJ said:

One tip - install them as far from the boiler as possible.

ChrisJ said:

The manufacturers like to set them up to slowly bake the motor/gear box directly over a drafthood for some reason.

DOH!

I didn't even think of that. When I installed mine I just did it the way they showed in all the pictures, not even thinking that it could just as easily have been mounted at the top of the pipe as the bottom, or thinking about how heat might damage the motor. What a dork I am.

I have nearly a 10 foot run to the chimney. Flue runs through a thin wall first so the damper is actually in different room than the boiler. Maybe why it has lasted so long.

Hap_Hazzard

I can't move mine that far away, but I can probably raise it a couple of feet--even more if I put it on the horizontal section. Is there any reason that wouldn't work? I've never seen one in that position, but I'm having a hard time convincing myself it wouldn't work.

PMJ

Hap_Hazzard said:

I can't move mine that far away, but I can probably raise it a couple of feet--even more if I put it on the horizontal section. Is there any reason that wouldn't work? I've never seen one in that position, but I'm having a hard time convincing myself it wouldn't work.

Will be fine. Mine is in that long run which might be 15 degrees off horizontal.