Condensation on Wood Stove / Outside Air Piping

[Coyoterun]

I skimmed through your post as I'm watching the hockey game right now, but if I understand correctly you assumed that all heat you put into the house was due to infiltration your air changes per hour will be inflated as you are ignoring the large amount of heat lost due to conduction through wall/ceiling/windows/etc.

So your actual infiltration rate will actually be a fair bit lower than what you calculated.

Correct. The calculations ignore both conductive heat loss and solar heat gain. I have no way to estimate those numbers. I'm fairly confident that solar heat gain is less than conductive heat loss, so the net should still be negative. I just don't know how much.

Also, the 1.08 in the formula assumes density of air at 70*F. So the air in my case will be cooler, more dense, the actual number would be greater than 1.08. That number is in the denominator in the equation, so it also means the actual CFM would be lower.

I suspect the actual infiltration rate in my house is closer to 200 than it is to 300, but that's only a SWAG at this point. It does seem pertinent to the current discussion tho.

 

[electrathon]

Thank you to the smart math people here. It drives me crazy that so many on here somehow believe that it is normal for a house to leak 1600cfm all the time. And they tell other people it is true. At some point even if you can't do the math common sense tells you that you do not leak all of the air out every few minutes.

 

[snavematt]

just disconnect the OAK, cover the end coming from outside with insulation, plastic wrap and some tape. Run your stove and see how your draft is. My house is pretty tight, and I don't run an OAK on my Explorer 2, I have about 25-35 ft of stack and it runs just fine.

 

[St. Coemgen]

I find the discussion on air infiltration has gone off the track a bit.

Trying to bring it back:

Any house will of course leak air. Even a super sealed and efficient minergy home. That is, given enough pressure, leaks from somewhere, in the wall, or around a window gasket, or whatever, will move in/out air. Simply: No earth based home can be used as a sealed environment for space travel.

Fact.

But that will be cold air flowing directly in from outside.

Potential problem.

Meanwhile, a heat exchanger will move air into a home, efficiently, and economically so as to retain indoor heat, and also by doing so should remove most internal negative air pressure causing cold air leaks into the home from other sources, and thus overall make the home warmer, and more energy efficient.

But of course, that is all only relevant on one having a modern, well insulate AND sealed home. So it is all relative. For example, if you have an old farm house with 1890 windows (I actually lived in one of those), then a heat exchanger is a waste of time, money and effort. And your wood stove will burn fine. Because, if you add up all the cracks sq areas, it may just equal to being as if you simply opened a window. Might as well toss money out that same window then.

 

[mminor]

I've read through this thread a couple times and clearly you guys are intelligent and well versed on OAK's.

Can you please advise me?

I will be adding a Northstar zero clearance fireplace as a bump-out / alcove on the main floor of my existing house which was built in 1955 (architect's drawing attached). The ZC fireplace comes with and requires the outside air kit for combustion. I have the option and would very much like to get the combustion air from my my basement (inside air) as opposed to pulling ice cold air from outside (Long Island New York) and running into all the condensation issues others are experiencing - not to mention all the cold outside air that will leak into the house via the OAK when the fireplace is not being used.

Can I safely get my combustion air from my basement (inside air) instead of pulling cold outside air for combustion?

Thanks in advance for all your advice and insight - I really appreciate it.

Matt

 

[lsucet]

I will say NO. it is the same that use it without the OAK from the beginning. Why to go thru all that trouble to have the same results.
that is just my opinion but i am sure somebody else will tell you the same. you just getting the supply air from different room. what can be different from basement and fireplace room? temperature maybe? the purposes of the OAK is bring/supply independent air for combustion from out of duelling and there are more to it than just supply fresh air, is just that sometime if houses are not that tight and well insulated, is hard to notice any differences.

hope this help

 

[electrathon]

What your missing and assuming is that he says a MIN. for health is 66cfm. THAT'S A MIN. for health reasons.
Hes not saying an average house has 66 cfm leakage. Only a SUPER TIGHT very small house will ever see a leakage rate that small.

Did you miss his next sentence?
"most houses older than 20 years have natural leakage rates far higher than this in winter"

I had my late '70's tri level tested in 2010. It had a leakage rate of 1775cfm! 1775 cfm equates to 4.58ACH50 in my house!

Note from my test.

"Given the conditioned floor area, house volume and external surface area of the home, this is considered average in regards to air infiltration."

So my house with 1775 cfm leakage is average for its size and age.

here is some other notes from my test.

"newly built energy star certified homes in WI average around 1.50 to 2.50 ACH50."

If my home was at the average of a newly built energy star certified home built 7 years ago assuming 2 ACH50 it would equate to 775 cfm!

If I had 66cfm leakage that would equate to .17 ACH50.

The tightest most efficient house standards, Passive House, requires .6ACH50. More than 3 times the 66 cfm.

Forget 66 cfm, its not the real world for air leakage, 660 cfm is a closer average of the houses out there.


Another gem.

"old farm houses can be as leaky as 10ACH50 or more."

I had no significant air leakage at my wood stove.

In my average leaky 40 year old house the 25 cfm for the wood stove is 3% of the air leakage. Insignificant.

I had the test done to improve the energy efficiency of my home. I followed alot of the recommendations.
If your serious about the energy efficiency of your home start with a good energy assessment and follow the recommendations.

You'll know what your leakage is and how insignificant 25 cfm for a wood stove is.

Karl,

Do you really believe that when your doors and windows are all closed that you have to replace all of the air in your house every 8 minutes? The reason that they were able to get 1775 CFM of leakage is because they pressurized your house! It is a false number if your are looking for how much CFM your house leaks. It works if you are only looking for a location. You are completely mistaken if you think that every 8 minutes you have to reheat all of your air. At the number you believe your house leaks that is how often you would have to do it. If you left the huge test fan in your doorway and it blows cold air in all the time, I stand corrected. If the fan has been removed and you closed your door, then you are mistaken.

 

[electrathon]

I've read through this thread a couple times and clearly you guys are intelligent and well versed on OAK's.

Can I safely get my combustion air from my basement (inside air) instead of pulling cold outside air for combustion?

Thanks in advance for all your advice and insight - I really appreciate it.

Matt

I also can not think of an advantage of drawing out of the basement. The main reason for an OAK is to not depressurize the house, drawing unheated outside air in to your living area. It keeps your house warmer and your draft working better. Drawing from another room should have no affect, positive or negative that I can think of.

 

[cd36]

I talked to rsf, the company that made my fireplace, and they recommended extending the outside air kit duct and add some traps to it. The traps will help keep warm air on one side and cool air on the other when not in use (skeptical, but ill try it) . The extra length will also give more time for the air to warmup before entering the fireplace so it won't condense as much.

I think it's true if the air were just a bit warmer it would be fine. A couple days after I took that pic I posted above the temperature was up to a balmy - 18c and the ice had disappeared (also had a good fire going, so I'm sure it's heat combined with the warmer air outside helped)

Sent from my LG-H812 using Tapatalk

 

[electrathon]

I am not sure how well it works, but there have been a few threads about bringing the air inlet pipe way down and then back up.

 

[cjmoran]

just disconnect the OAK, cover the end coming from outside with insulation, plastic wrap and some tape. Run your stove and see how your draft is. My house is pretty tight, and I don't run an OAK on my Explorer 2, I have about 25-35 ft of stack and it runs just fine.

Thanks everyone for all your help. I plan on disconnecting the OAK and leaving it disconnected. Covering the other end as mentioned. If I ever decide to connect the OAK back up, I have that option, but I'll add a damper of some sort if I ever do that. I do not notice any additional draft due to having it disconnected (maybe it's so small that I never would myself notice it).

I didn't think I'd get so much activity on my original post. This is a great resource.

 

[cjmoran]

The Outside Air Myth exposed.
A good an informational read.

your house is 10 years old
did you have a blower door test done?
does your home have a ERV or HRV?
Do you have exhaust fans in bathrooms, kitchen and from a dryer that exhaust to the outside?
Most of these exhaust ducts are no where close to being sealed when not running, they are letting air into your house if needed.
Unless the builder was into very energy efficient homes I doubt your 10 year old home is very air tight.
If it has neither a ERV or a HRV then I doubt its on the very air tight side of things or one would of been installed.

There are conditions that a OAK is beneficial and or needed. but until your house is very air tight you won't need one.


http://www.woodheat.org/the-outdoor-air-myth-exposed.html

I had a blower test done about a year ago on my furnace. No issues. I do not have an ERV or HRV. Yes, I do have various exhaust fans. My home is not an 'energy efficient home'. I'm going to go without the OAK. Thanks for the advice.