Controlling air on a CFM FW240007

[Stihl025]

I just bought (from Lowes) and finally installed a Century 1000 (CFM FW240007) into our basement. I tied it into a 6" stainless chimney liner that runs 23' through the middle of the house and crests at the peak of the roof. I have absolutely no problem with draft. Couldn't ask for better. The problem is that I am having problems controlling the air to the stove. The damper control at its highest works very well, but when I damper down, there seems to be very little change. It appears that it is getting air from somewhere else other than air control on the front. At first I thought it was the door gasket because there was that tiny little gap where the two ends meet, but rhen I realized that the air was coming from below. After using a butane lighter to locate the draft, the air is coming from around the edges of the masonry ash pan cover inside the firebox.

Does anyone use that opening to remove ashes? I don't use mine, nor do I plan to. I have always removed ashes with a shovel and bucket. Is it acceptable to use stove cement, or firebrick mortar to seal that opening?

I am sure that I am not getting the lowest setting out of my air control beacuse of that draft. Any suggestions?

 

[webbie]

Aha, you must read and maybe even hear about the Florida Bungelow Syndrome...

This is the article that was met with deafening silence by the stove makers - in fact, by the entire industry. But here it is:
https://www.hearth.com/econtent/index.php/wiki/why_stoves_overfire_from_too_much_draft/

If you want to listen to my latest Podcast with John Gulland (the author), and hear him explain it in his own words, check it out at:
https://www.hearth.com/podcast/podcast.xml

 

[Stihl025]

I read the article and a lot of good info. Should I try to seal that ash pan "brick" or just put in a damper? Not sure if anyone else has tried anything similar.

 

[EatenByLimestone]

When ash fills in around the plug your problem will end. The next one you will find will be fire and smoke escaping around the back of the stove and avoiding the secondaries.

I added a few firebricks on top of the gaps and it insulates and directs the smoke better. Laying a brick over the air tube will help that heat up faster too.

Matt

 

[Chettt]

That brick fits in its space only one way. Put the square in the other 3 ways and air will leak in until ash builds up in the groove. On mine, the metal pull up ring has to be north/south with more brick on the right side of the ring. After 4 fires you'll find the right seating position.

 

[Stihl025]

That brick fits in its space only one way. Put the square in the other 3 ways and air will leak in until ash builds up in the groove. On mine, the metal pull up ring has to be north/south with more brick on the right side of the ring. After 4 fires you'll find the right seating position.

I have tried the other three positions, came up with the north / south position as well as being the "best". But, no matter what, I found that they all let air into the firebox. Pull out your ash pan during a burn and hold a match up to the bottom of the brick and watch what happens.
Today, I used a high heat fireplace morter to seal the seat of the ash pan brick. See, even when ash would acculate in the grooves, my chimney draft was so strong, it would act like a blast furnace under that particular brick, no matter what the position of the brick. I had virtually no control over the damper. I just fired up my stove after a few hours of "dry" time, and the difference is amazing. I have complete control of the damper now. I highly recommend sealing the ash pan brick if you have this particular model of the Century.
Now, don't get me wrong, I was in Home Depot neb nosing around, and compared the ash pan lids / caps (whatever you call them) of a few different stoves. The Englander models use a very thick piece if steel. It looks as if it would seal under its own weight. Maybe something to think about later down the road. Have welder, cut off saw, and steel.....

 

[tradergordo]

I'll be honest, the first thing I thought of when I just read the TITLE of this thread was 'not the florida bungalow thing again', but in this case, I'd be willing to bet money that is NOT the problem. You need to fix the leaks first. But an important question no one asked - what is your flue/chimney like - how tall? what if any bends? inside or outside (where does it exit the house)? single wall or double? 6" or 8" or masonry w/ or w/o liner?

PA is a milder climate compared to most people with the florida bungalow problem. A damper or intake air restrictor is a TERRIBLE solution for a leaky stove problem.

Aha, you must read and maybe even hear about the Florida Bungelow Syndrome...

This is the article that was met with deafening silence by the stove makers - in fact, by the entire industry. But here it is:
https://www.hearth.com/econtent/index.php/wiki/why_stoves_overfire_from_too_much_draft/

If you want to listen to my latest Podcast with John Gulland (the author), and hear him explain it in his own words, check it out at:
https://www.hearth.com/podcast/podcast.xml

 

[Stihl025]

You need to fix the leaks first. But an important question no one asked - what is your flue/chimney like - how tall? what if any bends? inside or outside (where does it exit the house)? single wall or double? 6" or 8" or masonry w/ or w/o liner?

PA is a milder climate compared to most people with the florida bungalow problem. A damper or intake air restrictor is a TERRIBLE solution for a leaky stove problem.

I completely agree and I think that I have accomplished that with the sealing of the ash pan cover. My chimney is a 6" stainless flex inside a 6" (6 1/2") clay chimney. It stands 23' tall from the thimble to the top of the clay. Runs through the middle of the house and extends 3 1/2 feet above the peak (protrudes through the roof at the peak, so it is at the highest point of the roof). I have awesome draft. No question about that.

 

[stoveguy2esw]

ok i read the article, the biggest reason the industry shies away from commenting on it is simple. no 2 chimneys are the same , the 'florida bungalo" or whatever its called would be a worst case scenario as i see it, but if a stove is to work in it it must be engineered to do so, now , that leaves the manufacturer with "do i build a lot of "florida stoves" and have them burn like a forge in maine?" or "do i build a stove that works well in maine , and have to eat all the units i sell in florida?" a stove to be a realistic appliance for any national supplier must be capible of working in marginal conditions , but in my opinion , "marginal" conditions also include overdrafting chimneys as well as underdrafting ones. margins work both ways. from a manufacturers standpoint also the unit must be able to pass the stringent testing required for Ul listing and EPA certification. these tests will not allow adjustments for opening and closing past the norm for "marginal" flue setups. if they did , they wouldnt be as safe simply because if a consumer (who likely will not have a degree in thermal engineering) who wants to extend his burn time in a marginal flue setup and lowers his stack temps too far, could very easily set in motion the classic buildup for a flue fire. ie low stack temps building creosote , followed by a hot fire to ignite it. designing a stove to perform in a sick chimney , and still expect it to be able to handle an overactive chimney isnt exactly easy either especially when it must pass testing in every aspect. therefore chimneys should be designed to provide a draft overpressure that falls within a reasonable range. this doesnt happen. if you dont believe me , take a drive and look at the chimneys poking up from the houses in your area. the difference is staggering. designing a stove line that will work in sick chimneys as well as hyperactive ones,AND still meet EPA criteria is a pipe dream it simply isnt going to happen with the criteria that must be met these days. so , the adjustment has to be the chimney , not the stove. add a damper if the flue is too active, or apply the proper cross sectional code and proper flue height in relation to the roof if the flue isnt up to standard. but dont bash the manufacturers who are building to the standards they are required to build to.

 

[tradergordo]

Not quite sure we are all on the same page. The problem Gulland is talking about is how because of current EPA testing procedure and test guidelines, the manufacturers can't build stoves that can restrict intake air under strong draft conditions (which never exist in EPA test labs). Gulland offered several suggestions, but wasn't talking about normal customer accessible type controls. It can be a serious problem to have stoves overfiring in extremely cold climates or certain situations with excellent drafting chimneys (I kind of like Gulland's comment in the interview with Craig that there is no such thing as an overdrafting chimney). Flue dampers have drawbacks, but its one solution. No one was ever talking about engineering stoves to burn well in Florida. I don't quite like the phrase "Florida Bungalow" because its misleading - but it refers to a single story type house (i.e. the short stacks used in EPA testing, and may also allude to the lack of testing in very low temp environments).

ok i read the article, the biggest reason the industry shies away from commenting on it is simple. no 2 chimneys are the same , the 'florida bungalo" or whatever its called would be a worst case scenario as i see it, but if a stove is to work in it it must be engineered to do so, now , that leaves the manufacturer with "do i build a lot of "florida stoves" and have them burn like a forge in maine?" or "do i build a stove that works well in maine , and have to eat all the units i sell in florida?" a stove to be a realistic appliance for any national supplier must be capible of working in marginal conditions , but in my opinion , "marginal" conditions also include overdrafting chimneys as well as underdrafting ones. margins work both ways. from a manufacturers standpoint also the unit must be able to pass the stringent testing required for Ul listing and EPA certification. these tests will not allow adjustments for opening and closing past the norm for "marginal" flue setups. if they did , they wouldnt be as safe simply because if a consumer (who likely will not have a degree in thermal engineering) who wants to extend his burn time in a marginal flue setup and lowers his stack temps too far, could very easily set in motion the classic buildup for a flue fire. ie low stack temps building creosote , followed by a hot fire to ignite it. designing a stove to perform in a sick chimney , and still expect it to be able to handle an overactive chimney isnt exactly easy either especially when it must pass testing in every aspect. therefore chimneys should be designed to provide a draft overpressure that falls within a reasonable range. this doesnt happen. if you dont believe me , take a drive and look at the chimneys poking up from the houses in your area. the difference is staggering. designing a stove line that will work in sick chimneys as well as hyperactive ones,AND still meet EPA criteria is a pipe dream it simply isnt going to happen with the criteria that must be met these days. so , the adjustment has to be the chimney , not the stove. add a damper if the flue is too active, or apply the proper cross sectional code and proper flue height in relation to the roof if the flue isnt up to standard. but dont bash the manufacturers who are building to the standards they are required to build to.

 

[stoveguy2esw]

well , i might have went off half cocked a bit , but there are a few things that do need to be pointed out. first , not all single story chimneys are weak , i have a 15 ft chimney in my home that works perfectly. i have also seen 25 ft chimneys which meet the standard 10-3-2 rule that do not pull as well due to the structure being tight. all that said though , should the overdrafting chimney be taken into consideration , it would be nice , but how would that protect the homeowner who has a sluggish one from unwittingly dialing his stove back too far and dropping his flue temps into the creosote zone? the standard for testing is set up the way it is to ensure that a unit cannot be easily "underfired" creating an unsafe condition that cannot be otherwise controlled, i agree that an overdraw is not a great situation , but an overdampered situation can be just as bad if not worse. my biggest reason for the tirade that i launchedinto was over the apparant non response to the issue by the manufacturers. i know we do work to make our units as flexible as allowed by the standards that we have to work under, and im right proud of the product we supply. i may have been a bit hard about it , but it wasnt malicious, it just hit me the wrong way.

 

[Chell]

I'm really glad you asked this question. We just bought the same model to replace an old Hearth Mate, and it seemed like the older stove had better air control. Adjusting down seemed to have no effect at all. Go figure. We'll see how this new one burns for a while, and seal the ash pan opening (under brick) at least a bit if overfiring becomes a problem. The manual for the Century says no damper is necessary, and to either remove any existing one or to make sure it's open. Now I'm glad we didn't remove the stove pipe damper.

 

[Chettt]

Interesting topic. I have the stand alone 2000 sq/ft model and the stone seals perfectly. I do know what you guys are talking about when it didn't seat properly, it looked like a gas leak shooting out of the bottom. I like the ash drawer system and I would contact the company for maybe a replacement brick that fits better.

 

[tradergordo]

The problem is not a 15 foot chimney that doesn't work, if anything, the stoves are almost built for that. The problem is a 30 foot chimney in Connecticut, or a 20 foot chimney in Maine, causing stoves that cannot be turned down enough to burn out of control, possibly glow red, or maybe just have a 4 hour burn when it should be 8. Gulland's point was that the manufacturers DO have their hands tied - but no one is talking about the fact that their hands are currently tied or what to do about it. This can lead to problems when a manufacturer or dealer just assumes a stove is defective or has leaks if in fact the problem is that the stove isn't built to handle the strong draft that is present in a particular installation. I don't know if you got all the way down to the bottom of the article, but suggestions were:

1) The EPA and the committee responsible for the CSA B415 standard (which has the same problems) should acknowledge that when stoves are optimized to operate under test conditions, they do not perform as intended when connected to tall chimneys and in cold climates.

2) When designing new stoves or reworking existing models, manufacturers should develop air controls with a means of adjustment to deal with this problem. Such adjustments should not be readily accessible to the stove user.

3) Stove manufacturers and regulators responsible for wood stove emissions should consider it acceptable for a WETT certified technician (and the U.S. equivalent) to make air control adjustments when they encounter short burn times with stoves connected to tall, straight venting systems.

well , i might have went off half cocked a bit , but there are a few things that do need to be pointed out. first , not all single story chimneys are weak , i have a 15 ft chimney in my home that works perfectly. i have also seen 25 ft chimneys which meet the standard 10-3-2 rule that do not pull as well due to the structure being tight. all that said though , should the overdrafting chimney be taken into consideration , it would be nice , but how would that protect the homeowner who has a sluggish one from unwittingly dialing his stove back too far and dropping his flue temps into the creosote zone? the standard for testing is set up the way it is to ensure that a unit cannot be easily "underfired" creating an unsafe condition that cannot be otherwise controlled, i agree that an overdraw is not a great situation , but an overdampered situation can be just as bad if not worse. my biggest reason for the tirade that i launchedinto was over the apparant non response to the issue by the manufacturers. i know we do work to make our units as flexible as allowed by the standards that we have to work under, and im right proud of the product we supply. i may have been a bit hard about it , but it wasnt malicious, it just hit me the wrong way.