Are Dampers Legal?

[BKVP]

As an active participant in these forums, I often see references to the use of dampers. I receive PM's and emails from consumers every once in a while asking if they should install a damper. I don't respond to those inquiries.

As a manufacturer, we follow the Federal Register (law) as it pertains to the proper installation of our appliances. When the subject of dampers comes up, I tend to not respond for the above reason.

When a manufacturer tests a wood heater, they are required to test it as they will manufacture the product. Any modifications to air intake or exhaust that would enable the appliance to operate at a lower burn rate than as it was tested are illegal. So forgive me, but I am not trying to be evasive on such inquiries or posts, just sticking to the letter of the law.

Here is the actual wording from the 2015 NSPS. Yes, it's awkwardly written, but the intent is clear...with multiple follow-up conversations.

 

[stoveliker]

On the other hand, you specify an exhaust system in feet rather than the more appropriate draft quantity (underpressure).

If a chimney provides more draft than you tested with, and there is an appliance that decreases it to what you (mfg) need it to be, then the draft is not artificially lowered. Instead the artificial (because of the "100 ft tall chimney") high draft is put into specs for the stove ...

 

[showrguy]

Written by some Govt. agency, so clear as mud, right ??
I installed 2 key dampers in my 35’ stack (and somedays could use a third) for my King..
My argument would be.. I’m not trying to alter the low burn rate at all, I’m trying to achieve those draft specs !!

 

[MR. GLO]

Some stoves can not run safely or "clean" burn without a damper. The draft is too strong, especially during strong winds. Some manuals indicate setting the draft to a specific range. So I dont see that as "altering" or operating the stove illegally since it will burn better and cleaner, but using the damper to bank it below the manual draft settings, then I guess it would be altering the stove. Jotul manual indicates using a butterfly damper to set the draft. I would never install a stove without a damper. Its a good safety for flue temps. When the manufacture tests the stoves I would assume they set the draft to pass the epa test.

If the intent was clear the language would say, "No dampers allowed".

Be great to see more videos on using a damper properly. I haven't seen many.

 

[ABMax24]

What a frustrating interpretation of the law. In Canada at least, I can put a 40ft vertical stack (unless the manufacturer specifies a lower max height) on a stove designed, built and tested on a 15ft stack and be completely legal. Anyone using any kind of logic or having experience with such a stove knows that overdraft is a certainty and the stove is not operating anywhere close to the way it is designed or tested. Yet when a damper is installed on such a stove to bring draft to within the designed and tested specs and it quickly steps outside the rules.

Every hardware store around here sells key dampers or pre-built dampers in sections of double wall pipe. I don't see that changing anytime soon regardless of perceived or actual legality.

 

[stoveliker]

My point was that if dampers are not legal in BKs eyes, then advising a customer to install at any other stack height than 15' is not either - because it changes the exhaust system from that of the test.

This is all because the requirements are in feet (stack height) rather than the better draft measurement.

 

[jetsam]

So many things around wood stoves could be quantified and expressed clearly, but we choose not to.

Do manufacturers know what a manometer is? Yes. Do they want to get into trying to explain that to customers, half of which proudly refuse to read the instructions in the first place? Nope.

"Creosote condenses at 250°F; keep the coldest part of your flue above that." is an important concept for any wood burner to understand, and it's even pretty simple. How many wood burners do you know that can explain it to you? How many can tell you how they test to see if it's working on their installs, and what steps they can take if it's not working well?

The list goes on.

 

[stoveliker]

Sure, but if they don't do that, then there is no rational reason to outlaw dampers. And for BK to let slip many "against the letter of the law" things through, but not dampers.
It's just not consistent.
Numbers are.

I get why this won't happen. But the inconsistency does not make sense to me.

 

[BKVP]

What a frustrating interpretation of the law. In Canada at least, I can put a 40ft vertical stack (unless the manufacturer specifies a lower max height) on a stove designed, built and tested on a 15ft stack and be completely legal. Anyone using any kind of logic or having experience with such a stove knows that overdraft is a certainty and the stove is not operating anywhere close to the way it is designed or tested. Yet when a damper is installed on such a stove to bring draft to within the designed and tested specs and it quickly steps outside the rules.

Every hardware store around here sells key dampers or pre-built dampers in sections of double wall pipe. I don't see that changing anytime soon regardless of perceived or actual legality.

In at least a few instances, retailers have reported to me EPA contacted them to find out how many dampers they sell. It has been a few years (3-5) since I have heard about these inquiries.....maybe they read your post!!

 

[ABMax24]

In at least a few instances, retailers have reported to me EPA contacted them to find out how many dampers they sell. It has been a few years (3-5) since I have heard about these inquiries.....maybe they read your post!!

That's interesting, they're looking to know how many dampers are sold, but seem unwilling to look beyond as to the reasons why they are needed in the first place.

Our retailers are outside EPA jurisdiction thankfully, as am I.

 

[Highbeam]

I wonder how hard it would be to engineer a stove to internally and automatically regulate the draft with some sort of internal damper. Would folks install key dampers if they weren't needed? It's just another thing to adjust and clean around.

I for one dislike this new 15' tall chimney requirement that is so common with new stoves. It's way too tall for many single story homes but too short for two story homes. Chimney height is very install specific and largely out of our control.

 

[bholler]

I wonder how hard it would be to engineer a stove to internally and automatically regulate the draft with some sort of internal damper. Would folks install key dampers if they weren't needed? It's just another thing to adjust and clean around.

I for one dislike this new 15' tall chimney requirement that is so common with new stoves. It's way too tall for many single story homes but too short for two story homes. Chimney height is very install specific and largely out of our control.

Yes you are right about the 15' thing but honestly it splits the difference. It would obviously be much better if we had a way to adjust the stove to make it work over a wider range of draft. But I honestly think 15' is a better option because it means a standard 2 story install isn't that far beyond spec. And a standard 1 story isn't far under.

 

[stoveliker]

But "that far" is not "as tested" - which was the argument to (not respond or) not advice dampers...

A system with auto draft regulation should be possible given that most draft is measured mechanically (as is the bimetal thermostat in the BKs). Therefore getting an unpowered control, based on such mechanical input should not be out of the realm of possibilities.

 

[jetsam]

Yes you are right about the 15' thing but honestly it splits the difference. It would obviously be much better if we had a way to adjust the stove to make it work over a wider range of draft. But I honestly think 15' is a better option because it means a standard 2 story install isn't that far beyond spec. And a standard 1 story isn't far under.

Maybe someone could come up with some kind of device that could be inserted into the flue to restrict flow if draft got too high.

 

[Highbeam]

But "that far" is not "as tested" - which was the argument to (not respond or) not advice dampers...

A system with auto draft regulation should be possible given that most draft is measured mechanically (as is the bimetal thermostat in the BKs). Therefore getting an unpowered control, based on such mechanical input should not be out of the realm of possibilities.

Also, as we know, the 15’ ideal stack behaves much differently at 60 degreesF than at -35 degrees.

The wood furnace guys get to use barometric dampers.

 

[stoveliker]

Of course. That difference would be reflected in the physical measurement, and thus compensated for.

I don't claim to have insight in the business feasibility aspect, tho.

Barometric dampers would cool down my stack too much.

 

[Highbeam]

Has there ever been a barometric damper that worked mechanically? That is, without admitting room air into the flue? I’m imaging by use of a variable flue restriction.

 

[ABMax24]

It's doable, but reliability will be difficult as getting it to actuate on such low differential pressures when combined with the creosote from the stove trying to block/plug things off will be a challenge.

I think a traditional damper operated by a big bimetallic coil might be the best. The hotter the flue the more the damper closes, which makes sense as draft increases with temperature. It would also help regulate the burn in a stove, if the stove cools off the damper opens allowing more air to the fire hopefully eliminating smoldering.

 

[NorMi]

There's no reason all chimney draft variation can't be accounted for on the intake air controls side, but the system would need to be more precise and operate over a wider range than wood stoves are designed for today. You'd need a mass air flow sensor, or differential pressure sensor coupled with intake air temperature sensor and a robust throttle/air intake control damper. In the meantime they spec either a inches of WC draft allowable range (sensible-ish) or chimney height (silly). Not a big fan of baro's because of the flue gas cooling effect they have as mentioned, and you could automate a key damper to achieve the same broadband control effect, or (3) just design a better air controls system on the intake side.

 

[Highbeam]

There's no reason all chimney draft variation can't be accounted for on the intake air controls side, but the system would need to be more precise and operate over a wider range than wood stoves are designed for today. You'd need a mass air flow sensor, or differential pressure sensor coupled with intake air temperature sensor and a robust throttle/air intake control damper. In the meantime they spec either a inches of WC draft allowable range (sensible-ish) or chimney height (silly). Not a big fan of baro's because of the flue gas cooling effect they have as mentioned, and you could automate a key damper to achieve the same broadband control effect, or (3) just design a better air controls system on the intake side.

Woodstock has a bimetallic coil control of secondary air and PE uses a barometric control of secondary air. Of course BK runs all intake air through a thermostatically controlled throttle body.

You’re right, this could be taken care of on the intake side.

 

[john26]

Maybe stove manufactures could make a device like a damper built into the stove and tested on the stove with adjustments in 5' increments over the 15' or whatever the minimum chimney height is for that stove.

 

[shoot-straight]

my dealer raved the use about baro dampers on his stoves. he is no longer in business.

 

[mellow]

I thought with all the replies this was a topic about dampers on Inserts 😆

 

[jetsam]

There's no reason all chimney draft variation can't be accounted for on the intake air controls side, but the system would need to be more precise and operate over a wider range than wood stoves are designed for today. You'd need a mass air flow sensor, or differential pressure sensor coupled with intake air temperature sensor and a robust throttle/air intake control damper. In the meantime they spec either a inches of WC draft allowable range (sensible-ish) or chimney height (silly). Not a big fan of baro's because of the flue gas cooling effect they have as mentioned, and you could automate a key damper to achieve the same broadband control effect, or (3) just design a better air controls system on the intake side.

And when you increase the range of operation so it's wide enough to work in the real world, you can no longer get your EPA certification because the stove turns down too low for the test setup.

So you design your low range to work with the test setup, and then the guy with the new stove on the 30 foot stack shows up here to complain that his stove is uncontrollable.

And even if you went the opposite way- to devil with epa testing and you're going to be a black market underground stove company selling illegal stoves that work under a wide range of conditions- you'll then get the guys with 10 foot stacks and 4 90s going out complaining that your stove is a creosote machine.

So while I wish regulation allowed for a lot more range of control on stoves, the end users will screw it up no matter what regulations we do or don't implement.

Wood burning safely takes a certain amount of understanding and practice, and I doubt that a high percentage of wood stove owners have what I'd consider a basic minimum of knowledge there.

I'm sure barometric dampers are absolutely fine for some people (specifically those who feel like running a brush through their flue once a week), but it's not something to tell the general public to add to their setup.

 

[john26]

"The Series B device is driven by a predictable increase in chimney updraft at the beginning of Stage 2 due to the rise in exhaust temperature when the gasified resins ignite. The increased updraft draws a balanced pivot plate open, uncovering an intake opening to provide the "boost air" needed to ensure complete combustion of the volatile gases. Unlike the original EBT device, which delivers the boost air to the primary fire, the new device feeds the extra air to the secondary flames only. The operator retains control of the burn rate of the primary fire, and longer burn times are easier to achieve." courtesy of Tom Oyen

I understand the 2nd generation EBT works allowing more air or full air into the secondary at the beginning of stage 2 then restricting airflow to prolong the coaling stage and extend overall burn time. I don't see how this could prevent over fire during the secondary stage. Most of us with tall chimneys need to reduce daft during that part of the fire. The only way I see this being able to work is if it closed the primary air at the same time, but I am not sure would prevent an over fire, that would increase fire box temps?
On a Lopi freedom I tried decreasing primary and secondary air I mostly had I ended up with less complete combustion, lots of soot on glass. The only thing that helped slow the burn and lower stove top temps during the second stage was closing a flu damper.