Worst-Case Depressurization Test

[kmachn]

We've been burning wood ~4 winters in our fireplace, and last year installed an EPA wood stove in our basement. We love it. We have become more energy concious and recently had an energy auditor evaluate our home (BPI certified). It was helpful, but he is REALLY annoying me about our wood stove. He is very concerned about the potential for CO poisoning and wants to come back to do a worst-case depressurization test. He says he has some independent studies which show some negative outcomes and the risks, which he will send to me. I have no intentions of getting rid of our stove, but would really like some factual arguments (perhaps some data) to make a strong case for why I should keep it. I know there is lots of experience and likely some anecdotal stories which are great support for me, but none that will justify my case with him. I've read several posts on hearth.com about CO risk and poisoning, and of course have detectors installed.

Any studies/information (perhaps even some science on the draft/burning process & CO production) that could help me speak more intelligently? Thanks

 

[oilstinks]

dont see how if the stove isnt dumping the exhaust inside the house

 

[kmachn]

You're exactly right! I haven't had any issues, but then again, I can't recall a time when we've had all of our exhaust fans, clothes drier, kitchen range hood, etc. going at the same time. His argument is that under the "right conditions" (nearing end of burn cycle so reduced draft, strong wind outside, exhaust fans going, etc.) then it could really cause some issues. It looks like the EPA stoves really reduce this. We also have a long chimney from the basement (I think it is ~24 ft) so I would think that would reduce the risk. And, if the control is set low (which is what I have done after the secondaries kick in) then I would think the risk would be lower? Am I right in understanding that?

At any rate, any quantifiable data? If I had a manometer I would just do the worst-case depressurization and relieve my concerns, but still wanting to be prepared.

 

[oilstinks]

I guess anything is possible but not likely i wouldnt think. Just keep some CO detectors and keep the batteries changed. We got some CO detectors at our fire dept we can use. your local dept probably has them too .firefighterjake might can add more on that. If you can get them to come over try that worst case senario an see what you get. Give them a call and ask the worst thing they can do is say no but if you called me i would come over for a small donation to dept since we are volunteer.

 

[Rob From Wisconsin]

Sounds like to me he wants "job security"......

 

[begreen]

If you subject a house with a woodstove to enough negative pressure eventually you probably reverse draft, especially during mild weather. Is this a common issue for your home and lifestyle? If you are concerned, by all means take actions to mitigate these concerns like CO detectors and an outside air connection for the stove. However, you do need to exercise a bit of common sense here. If the possibility of achieving this level of negative pressurization in real world circumstances in negligible, then perhaps the CO monitors is sufficient.

 

[kmachn]

LOL Well, he's not charging me for the second visit. I think he is really trying to find every little detail he can to put in his report and make recommendations. I know that part of the BPI audit includes testing for the safety of gas appliances, so he is trained on that. We do not have any, our home is all electric. But, since wood stoves do work by combustion, I think he feels an obligation to test and be sure. I'm not inclined to argue with the test, who knows...maybe I'll learn something about it. Nonetheless, we have had fires going in both our upstairs fireplace and basement EPA stove without any backdraft issues. I can't say for sure that this has happened while my wife was running the clothes dryer, range hood, bathroom exhaust vents, etc, but there really seems to be adequate air infiltration to support these things.

I'm not opposed to installing a device to add combustion air, (either into the stove or into the whole house) if it is necessary, I just want to intelligently make the point that these things are more safe than he gives them (little) credit for.

oilstinks - I will try the fire department to see if they can give me a little test. You're right, it never hurts to ask!

 

[begreen]

Sounds good. You are collecting data and are taking a level-headed approach toward decision making. From what you've described, negative draft doesn't sound like an issue, but good to have a careful attitude.

How has the Cumberland Gap been working out for you?

 

[kmachn]

BeGreen - I think you touched on a point that is getting at what I would like to know. You mentioned that the likelihood of a "reverse draft" is increased in more mild weather. So, does colder weather improve draft, reducing the likelihood of a backdraft? Likewise, would the longer chimney improve this? Again, just trying to learn all of the different factors so I can make a stronger case (and perhaps, become more comfortable in my own understanding).

I don't think my lifestyle factors would support all of these things happening at the same time, but we have 4 small children (ages 4 months to 5 years) and as they grow older and become more independent, it does increase the likelihood of multiple appliances/fans pulling air from the home. I still doubt it is enough over the 3800 sq ft (both main floor and basement) to cause a negative pressure, but it is good to be thorough and in some cases, conservative.

 

[kmachn]

I really like the Cumberland Gap. I have to say I am not the most knowledgable about the different stoves, but we have a local seller who used to know my dad pretty well, so I chose to go with them and they only carry the QuadraFire line. I realized last year that a stove top thermometer really didn't work because of an air gap between the firebox and stove top, so I used an IR gun last year and purchased a Condar flu thermometer for this year. I watch the fire, but am finding I lack the experience to always know when it is hot enough. By nature, I am a "quantify it" kind of guy...I always like to compare objective numbers, to a fault. So, I am hoping that having the flu thermometer will help me better understand when the fire is going good enough to start cutting down the air...use both tools (thermometer and watching the fire) to get a better understanding.

 

[begreen]

Cold weather definitely improves draft and reduces the possibility of backdraft. A taller chimney will usually, (but not always) have stronger draft. Here are a couple good articles on the topic:

http://www.woodheat.org/locating-chimney.html
http://www.gulland.ca/florida_bungalow_syndrome.htm

 

[kmachn]

Thanks BeGreen, that definitely does help to better understand what is going on. The Florida Bungalow Syndrome...I knew the stoves were tested at ~15-18 ft chimney length, but I had no idea it was at 80 degrees F outside ambient. The second link had a table for estimating pressure differences (in Pa) depending on chimney length and temperature differences of ambient air and average chimney temp. Assuming 40 degrees F (more moderate weather), what would be a good avg flu temperature to use? I'm conservatively guessing 400F, no idea what the top of the chimney could be but I'm thinking the bottom (right at the firebox) is at least 800F-900F, correct?

Does anyone know how an EPA stove would compare to other combustion appliances for a worst case depressurization test? I found a chart that gives some "recommended levels" in terms of kPa, but not sure if a high number or low number is better. My understanding is that if you create negative pressure in the house, then having a higher number (more positive pressure) in the house is better (meaning less depressurization)? The chart listed an "air-tight" stove (which I assume means the new EPA models) as -10Pa was considered safe. Most others were higher numbers, including a fireplace of -3Pa. So, if my home is >-10Pa (closer to zero), the EPA stove would be considered lower risk, correct? Also, based on the table in the second (Florida Bungalow) link, I'm guessing the pressure differences would be about 44Pa (400 degress temp. difference & 25 ft chimney length) or higher. So, as long as my home is >44Pa, I shouldn't have to worry about reverse draft? Would that be another way of looking at it?

Another question about CO and chimney draft. When it gets to the end stages of burning (coaling?), less heat is produced and therefore increases the risk of reverse draft, right? During this stage of burning, is there more, less or the same amount of CO created? I think I learned that there were less air-polluting gases at this stage, but not sure if that holds true for CO.

That's a lot, thanks to anyone wise enough to help pull this all together.

 

[MasterMech]

Wouldn't installing an outside air kit put the kabosh on this issue once and for all? If all the combustion air intakes are ducted outside and the stove gaskets are good, then negative pressure in the home would be a non-issue. If memory serves, gas furnaces have a well sealed intake duct that is routed outside, correct? Isn't this the same concept?

Tell your inspector to put that in his firebox and smoke it.

 

[Backwoods Savage]

I have to agree with BeGreen all the way.

No quantifying data but I can tell you that I've been around wood heat almost my whole lifetime and I'm several years past retirement. I've also known probably hundreds of folks who burn wood for heat and a few burn coal. Yet I can say that I have never heard of any issues with CO. Nor have I ever read of any issues. Shoot, hearth.com is the first place I've ever heard about folks putting in co monitors when heating with wood. We have fire alarms but had never even thought about a co monitor.

I doubt there would be much data on CO issues just because of it not being such an issue as some feel it is. Is it a good idea to have the monitors? Yes.

 

[Jags]

The Cumberland is OAK capable. If a problem of negative pressure is found or can be realistically created, there is your solution. "Realistic" is the X factor in this. If the dude is using a large fan to depressurize the house and it starts peeling the wall paper off of your walls, its probably NOT a real life test.

NEXT!

 

[Todd]

Is your fireplace flue on the same chimney as your basement stove, side by side? If so he may be worried about the basment stove exhaust reversing back down the fireplace flue. Many have come to this forum with this problem including me.

 

[kmachn]

Thanks for the feedback. I know he will not be using a large fan to depressurize the house, just the existing fans in the house. That would include the kitchen range hood, 3 bathroom exhaust fans and the clothes dryer. This makes it "realistic" for my home, but it is considered "worst-case" and in my opinion not "realistic" because the likleihood of all of these going at the same time is highly unlikely. As my children get older, however, I suppose it is possible that the clothes dryer could be running while my wife is cooking and 3 of the other 5 of us could be in each of the 3 bathrooms with the fans on. Although, I would think that if that many people are home and awake, the stove would be actively burning (hot) and would have a better draft, therefore would be less likely for reverse draft. So, again, I wouldn't even consider that "realistic". I'm really hoping the numbers are well within limits so he can see by his own test it is perfectly safe without any additional intervention. I would prefer not to add an OAK if I do not need to, but I have contacted our local dealer to find out some more details (i.e. cost, ease of installation in basement, etc.). Any special considerations with installing an OAK, or just connect outside air to connection on stove? Since it is surrounded by concrete walls, any problem with the outside combustion air coming from above the stove (if it's opening is at the rim joist) and dropping down into the stove? Are there any undisputable disadvantages to an outside air combustion kit? I realize enough from perusing hearth.com that there is a lot of debate and I don't want to get going down that road, just wondering if there is an agreeable disadvantage (i.e., cold air entering and cooling stove and therefore living space when not in use).

Yes, the two chimney stacks are next to each other but are staggered 18" apart, vertically. I do not remember how far apart they are from each other horizontally, but they are not butting up side-by-side. There is at least 12", but I'm thinking it may be closer to 18". Nonetheless, experience last winter we did not have ANY backdraft issues from either the wood stove or fireplace regardless of the combination of their use (i.e., wood stove only burning, fireplace only burning, both burning, etc.).

 

[Jags]

I wouldn't put too much into this, unless the dude comes back with problems. He may walk away satisfied and then you are on your way.

 

[jimbom]

1. For peace of mind, you might consider running your own little test. Get your stove to the point of hot coals when it is warm outside. Put your CO monitor near the stove. Turn on all the fans and dryer. If no alarm, light a punk and see if the stove is exhausting at any seam or opening. Repeat at any firing rate the inspector predicts a problem might arise.

2. Regardless, assume worst case and keep the CO monitors tested and in good working order.

3. Sleep soundly.

Not to many of us from Missouri on this forum. Which I find interesting since we are surrounded by thousands of acres of excellent firewood. I guess natural gas is so cheap and wood stoves are so expensive that most don't think about wood.

 

[tfdchief]

Others have covered this pretty well and I agree. I just want to add one more thing. This "worst case...." is capable of creating CO problems with more than wood stoves. I see it frequently with gas water heaters and furnaces......to many exhaust fans on before the appliance comes on, i. e. a cold flue, and the fans start getting there air from the flue, creating a down draft...appliance turns on....CO detectors go off. This is usually associated with poorly vented appliances but not always. Sometimes conditions are just right. Just saying, this problem could occur in any house. Modern homes are very tight and sometimes that has to be remedied with make up air. Also why CO detectors are so important.

 

[kmachn]

JimboM - I agree, surprising how few wood burners there are in my area. In fact, I have ~3 full chords of firewood and routinely get comments on the "large" amount. I smile with pride, because I plan to grow that number each year! We do not have NG where I live, I would have to use propane. Personally, I feel like "free" heat from a renewable source is better than propane.

tfdchief - I get it, any combustion appliance could create problems. I don't know why he has such an issue with wood stoves, although he did make a comment that a gas furnace (I'm assuming water heater, etc. also) are designed to shut-off if there is a draft problem. I'm not real familiar with how they work, so I don't know if he is correct or if I understood him correctly. But, it seems to me that even a "fail-safe" can become damaged and lead to problems from a gas-venting appliance. From what I have read here on hearth.com, this is actually more common than the wood stoves.

 

[kmachn]

OK, so I've gotten a few things.

1) I'll try a couple of tests this week, including firing up the stove (we're going to be sweating bullets that evening) and doing a worst-case scenario and measuring the CO output, if any.

2) Try to get a manometer from a friend and do a "pre-test" before he comes back out. This should help tell me the pressure differential ahead of time so there are no surprises. Help put my mind at ease.

3) Find out the cost/installation procedure for an OAK designed for my Cumberland Gap.

It sounds like all of the testing is going to be WAY conservative, so even if I get results that are less than desirable, they are unlikely to be repeated under realistic circumstances. Even for those 1 in a million times that it may occur, that is what the CO detectors are for.

I'll report back with updates as I get things figured out. Thanks for the lessons

 

[3fordasho]

I've found one situation where it was easy to make the chimney reverse draft - leave the attic hatch open and try and start the stove. Lots of smoke out the stove's air intake. A case of where the house itself acted as a better chimney than the wood stove's chimney. I've never tried opening that hatch once the stove and chimney were up to temp, in that case I would suspect it would not reverse draft. One thing about a reverse drafting wood stove chimney, you know about it in a big hurry unless you're down to burning up the coals and the end of a burn.

 

[tfdchief]

I've found one situation where it was easy to make the chimney reverse draft - leave the attic hatch open and try and start the stove. Lots of smoke out the stove's air intake. A case of where the house itself acted as a better chimney than the wood stove's chimney. I've never tried opening that hatch once the stove and chimney were up to temp, in that case I would suspect it would not reverse draft. One thing about a reverse drafting wood stove chimney, you know about it in a big hurry unless you're down to burning up the coals and the end of a burn.

Yep, it is called the "stack effect" or "chimney effect". Your chimney becomes part of the inflow for the house that is now the chimney, so to speak.

 

[kmachn]

OK, so I've gotten a few things.

1) I'll try a couple of tests this week, including firing up the stove (we're going to be sweating bullets that evening) and doing a worst-case scenario and measuring the CO output, if any.

2) Try to get a manometer from a friend and do a "pre-test" before he comes back out. This should help tell me the pressure differential ahead of time so there are no surprises. Help put my mind at ease.

3) Find out the cost/installation procedure for an OAK designed for my Cumberland Gap.

It sounds like all of the testing is going to be WAY conservative, so even if I get results that are less than desirable, they are unlikely to be repeated under realistic circumstances. Even for those 1 in a million times that it may occur, that is what the CO detectors are for.

I'll report back with updates as I get things figured out. Thanks for the lessons

It's been about a month and a half but I wanted to wrap this up, and I came up with a follow-up question. I fired up the Cumberland Gap and have not had any CO output measured. My detector has a digital readout (although the manual doesn't say the minimum level of detection) and didn't show anything. Since then however, I have done quite a bit of air-sealing. My friend didn't come through with the manometer, so no dice on my own test. It is a moot point anyway, since I read more and decided to follow the advice of those above and purchase an OAK for my Cumberland Gap...which leads me to my follow-up question.

The OAK for the Cumberland Gap uses a 4-inch flex pipe. Since the stove is in my basement and it will run up the concrete wall to vent through the rim joist, I would like to try and hide it in the finished wall (which will be metal stud, unfaced fiberglass batts or rockwool insulation, covered with cement board and stone). Since the metal studs are ~3 5/8 inches, could I reduce to a 3 inch pipe to hide this inside the wall or would it be too restrictive? I could also pull the wall out from the concrete 1/2"-1" when I install, but would prefer not to do that. My dealer says that 3 inch would probably be OK, or I could "oval" the flex pipe within the stud bay, but thought it better to get another opinion.