Where to install damper on stove pipe

[macgyverman]

TL;dr : Is there any reason you can't install a damper directly on the stove outlet?

Hi all,

As per my other thread, I was having trouble getting heat out of a Drolet Escape 1800. I've since purchased an exhaust damper and it has increased the heat output considerably.

My original setup looks a bit like this. That is, an adjustable length coming right out of the stove and up to a 90 degree elbow.

The stove pipe manufacturer's own instructions state :

Note: Plan the fixed and adjustable measurements that you will require in advance. Adjustable or slip sections of connector should always be installed above a damper.

This meant I had 2 options:
- Replace the brand new adjustable pipe coming out of the stove with a fixed length, damper, and shorter adjustable length.
- Install the damper directly on the stove

I wrote to the manufacturer to confirm that it was acceptable to install the damper right on the stove outlet, and then connect the stove pipe. Not getting a reply, I went ahead with that install and it's been working fine.

I just got a reply back stating : The damper must not be installed directly on the stove. You may install it above your adjustable length.

So they are contradicting their own install manual....

Anyone have knowledge if there is anything wrong with putting it directly on the stove? Installing it above the adjustable length would put it out of reach for my wife.

 

[kennyp2339]

You dont want any portion of a damper going below the stoves flue collar and entering the upper baffle area of the firebox, there are flue collar adapter w/ built in damper that install onto the stoves flue collar, just remember that the handle will be much hotter then if the damper was installed 12-18" above the flue collar.

 

[macgyverman]

You dont want any portion of a damper going below the stoves flue collar and entering the upper baffle area of the firebox, there are flue collar adapter w/ built in damper that install onto the stoves flue collar, just remember that the handle will be much hotter then if the damper was installed 12-18" above the flue collar.

Thanks for the answer!

The damper itself doesn't protrude more than 1/2" beyond its body when it's fully open. Since the stove adapter is about 2", the damper doesn't go into the stove body at all.

In that case, would there be a problem? I am having a hard time understanding why you couldn't install the damper directly on the stove. It might get a bit hotter, but it can't be much worse than 12" up from the body. The handle doesn't appear to get too hot to adjust as things are.

 

[stoveliker]

I think the reason lies in the fact that a damper alters the gas flow pattern. It creates additional turbulence. If you do that near the stove, you may end up with undesirable outcomes - e.g. significantly decreased flow even when the damper is fully open due to e.g. an favorably placed vortex. Remember that stoves are engineered with gas flow as one of the main issues.

Nevertheless, do the experiment, keep an eye on things, and let us know. It could work fine.

 

[macgyverman]

I think the reason lies in the fact that a damper alters the gas flow pattern. It creates additional turbulence. If you do that near the stove, you may end up with undesirable outcomes - e.g. significantly decreased flow even when the damper is fully open due to e.g. an favorably placed vortex. Remember that stoves are engineered with gas flow as one of the main issues.

Nevertheless, do the experiment, keep an eye on things, and let us know. It could work fine.

That's a good point.

As of yet, I've only had positive outcomes from having the damper in this location. My wood consumption is down and my heat output is up. The flue temp is also much more reasonable. It peaks at 1100, but usually hangs around 900F, even with the stove on full open and a full load.

I'm also getting a better burn up, although I'm finding a lot more dead coals than I'd like in the morning.

 

[stoveliker]

More heat from less wood is a great result.

I find 900 F in the flue still quite high. People rarely run stoves fully open (unless a stove is undersized for the space, or e.g. it's "polar vortex cold" outside). So are you able to run your stove at e.g. 1/4 open and satisfy your heating needs? And what are the flue temps then?

Reaching 900 F for a short time is not an issue. But if you still need to run more than half open all the time: I do know of folks having/needing two dampers in their flue. Kenny above is one of them. Not sure how that would impact the turbulence thing, and what the best practice is with respect to their separation - but it's worth keeping in mind that it can be done.
(I did read the other thread, at least for a while, but forgot the height of your stack. I do vaguely remember a lot of other possible causes for "not enough heat" were mentioned there.)

As with any change to your system, keep an eye on your flue stack and cap/screen - a damper will (as you've seen) decrease temps. That could affect the speed of build-up in your pipes. I would normally advise to run a brush thru the pipes a bit more often so you can see what this change is doing to the pipes. Though at 900 F I would surmise (... nice guarantee, eh?...) that's not an issue yet.

 

[EbS-P]

This is where I installed mine. I did some thought if I wanted key in the front or side. Decided side was best for air flow but meant adding a damper control through a surround was more important.

It may not be ideal location but it works. More turbulence may mean more smoke roll out if the damper is left closed but I don’t see burn characteristics changing that much as the baffle / air deflector opening probably has the most effect on flow inside the firebox.

I do think there is secondary/primary air ratio that they shoot for with these fixed secondary air stoves. I don’t think and this is a guess that it is with air full open. To me anything over 50% is start up territory.

 

[macgyverman]

More heat from less wood is a great result.

I find 900 F in the flue still quite high. People rarely run stoves fully open (unless a stove is undersized for the space, or e.g. it's "polar vortex cold" outside). So are you able to run your stove at e.g. 1/4 open and satisfy your heating needs? And what are the flue temps then?

Reaching 900 F for a short time is not an issue. But if you still need to run more than half open all the time: I do know of folks having/needing two dampers in their flue. Kenny above is one of them. Not sure how that would impact the turbulence thing, and what the best practice is with respect to their separation - but it's worth keeping in mind that it can be done.
(I did read the other thread, at least for a while, but forgot the height of your stack. I do vaguely remember a lot of other possible causes for "not enough heat" were mentioned there.)

As with any change to your system, keep an eye on your flue stack and cap/screen - a damper will (as you've seen) decrease temps. That could affect the speed of build-up in your pipes. I would normally advise to run a brush thru the pipes a bit more often so you can see what this change is doing to the pipes. Though at 900 F I would surmise (... nice guarantee, eh?...) that's not an issue yet.

I guess I would need more of a baseline with the system before the damper. I'll go up and have a look at the chimney at the end of the season. Given the temps, I can't imagine I'll get much fowling.

I agree with both you you that I probably shouldn't be running it on full open, but I'm having a hell of a time getting the stove up past 500F surface temp without that. This has been the only way to get the house "uncomfortably hot", and even then, it only happened once. I usually need to run the stove near full open to raise the house temp. Anything less and it stays stable or the furnace has to kick on if it's really cold out.

The stove may be undersized, but if it is, it can't be by much. It's rated at 2000 sqft for my climate zone. I'm not sure how they calculate sq ft based on stories, but the entire floorspace of the house is 2400 sq ft counting the basement. I have a hard time believing it's undersized given that it's nearly the biggest unit they make and our house is quite small for a detached home. Most run at 3000 sq ft + if you count everything.

 

[macgyverman]

This is where I installed mine. I did some thought if I wanted key in the front or side. Decided side was best for air flow but meant adding a damper control through a surround was more important.

It may not be ideal location but it works. More turbulence may mean more smoke roll out if the damper is left closed but I don’t see burn characteristics changing that much as the baffle / air deflector opening probably has the most effect on flow inside the firebox.

I do think there is secondary/primary air ratio that they shoot for with these fixed secondary air stoves. I don’t think and this is a guess that it is with air full open. To me anything over 50% is start up territory.

So you installed yours straight on the stove?

The chimney manufacturer finally got back to me, and apparently the issue with putting it on the stove has to do with possibly damaging the stove. They suggested I contact SBI. I've reached out and am awaiting a reply.

 

[begreen]

Some damper assemblies, like the DuraVent DVL are built into the appliance adapter, right off the stove. Yes, this placement may affect the stove operation. I am testing one this season on our stove and it is a mixed bag. Even wide open there is a notable decrease in the draft and a greater tendency for the stove to spill a little smoke. That said, flue temps at peak burn have dropped notably too.

 

[EbS-P]

I have an insert and an appliance adapter connects the insert to the flex liner. Hole is probably 1.5” blow the top of the adapter and centered in the amount of liner that sticks into the adapter. The cast damper just barely protrudes into the stove when it’s open.

 

[macgyverman]

I have an insert and an appliance adapter connects the insert to the flex liner. Hole is probably 1.5” blow the top of the adapter and centered in the amount of liner that sticks into the adapter. The cast damper just barely protrudes into the stove when it’s open.

That's pretty much exactly what I have. I didn't get why the damper position would cause and issue. Seemed odd that the company said not to do that.

I'll wait on SBI and see what their take on it is.

 

[macgyverman]

FYI : SBI got back to me. They have confirmed that the damper can be installed directly on the stove output.