Interesting discussion elsewhere on "Makeup Air" for woodstoves

[oldspark]

"When there are multiple appliances passively vented (including the wood stove), there will be winners and losers WRT flue reversal."
Why cant a passive system deliver enough make up air?

 

[LLigetfa]

"When there are multiple appliances passively vented (including the wood stove), there will be winners and losers WRT flue reversal."
Why cant a passive system deliver enough make up air?

I am talking about passive system that don't deliver any make-up air. They rely on the building to be leaky enough to provide the makeup air. The problem is that there are a lot of well intentioned DIY'ers with big calking guns and cans of sprayfoam desparately sealing up all points of cold air ingress to reduce their fuel bill.

Many modern homes have already addressed the issue of general make-up air and/or direct vent appliances that draw dedicated outside air. Even there some DIY'ers will seal off the make-up air duct because without the furnace running, it becomes a cold draft spilling out a cold return duct.

 

[oldspark]

I was refering to a "true passive system", one designed to bring in make up air, leaky windows is just that leaky windows.

 

[LLigetfa]

I was refering to a "true passive system", one designed to bring in make up air, leaky windows is just that leaky windows.

An example of a "true passive system" that vents through a vertical flue without the aid of ablower and provides its own makeup air is a woodstove with an OAK.

There are of course some direct vent appliances that exhaust directly out the side of a home and also draw outside air without the aid of a blower. I think they are generally called "direct vent". In some cases they can be adapted to vent vertically through a double flue. There are also appliances that direct vent with the aid of a blower and draw outside air.

There are also "power vent" appliances that consume indoor air and the purpose of the blower is to combat the NPP.

 

[oldspark]

You seem to be able to confuse me at will today, OAK hooked to a wood burner is not passive, passive would be air brought in the house and used by what ever needs it such as brough in from a vented attic. Or am I wrong in my thinking.

 

[LLigetfa]

Sorry, didn't mean to. Passive can have many meanings. Passive solar means without the aid of mechanical devices. Passive circuits in electronics could mean no gain or energy source. Passive ventilation is air moving naturally without the aid of a blower.

 

[madison]

Basically to qualify for an energy star home. the leakage can't exceed 6% of the Home square footage.

OK, 6% of a 1000 sq ft home is 60. Is the leakage rate then to be less than 60 ?? I'll seek Wiki for info and post below

But is that : ml, cubic ft, ?? and ?? per day, hr, min ?? For energy star compliance?

Thanks for the info BG and LL!

Wiki seems to suggest the measurement in various ways:
1. Airflow (m3/sec)
2. Another common metric is the air changes per hour at a specified building pressure

 

[HotCoals]

As I recall there is a screen on the bottom of my stove where the OAK hooks in and I KNOW there is one on the outside.

I calculated that my 1600 SF house has about 12,800 CF of air assuming 8 foot ceiling (a little more if you have some vaulted ceilings like I do). So if a stove consumes 10 CFM of air per minute, it would take about 10 hours to consume the air in a home. Or put another way, the air would have to seep back into the house to replace itself every 10 hours or so. Then you have the issue of if you ever open any doors.

In my opinion, the lack of scientific evidence or evidence based data is a major flaw of the article. It's all conjecture. There was also an assertion (at least it was interpretation), that because EPA certified stoves are more "efficient" they consume less air. I would submit they require they require roughly the same amount of air to combust the fuel, the difference is how much heat goes into the space it's heating, instead of up the chimney.

I think you are on the right track.

Heck a bathroom vent fan probably sucks out 3 or 4 times the amount of air compared to a wood stove..for sure a cat stove on low cruise.

Until someone can show me a vid ..some test where they got a stove without a oak to spill smoke out the intake..I call bull.
You can run all the dryers and exhaust vents all you want in the vid I speak of..I doubt you can do it.

I have had 3 bath vents on..range vent ..clothes dryer,while burning wood...all was fine.
2500sf house..fairly tight.
Maybe some super duper insulated house of 1,000sf..that would be like living in a thermos bottle...and would need a air handler..which kinda defeats the super duper insulation imo.

 

[SKIN052]

I live in a new home built to code, 3 years old and tight as a drum in my opinion (but lets be reasonable). Two baths, kitchen vent, HVAC, 2650 sq/f, etc. Stove was installed 2 years ago and I have yet to notice the stove is robbing air from from the house. Where does the idea originate that a OAK is a must in new homes?

 

[semipro]

As I recall there is a screen on the bottom of my stove where the OAK hooks in and I KNOW there is one on the outside.

I calculated that my 1600 SF house has about 12,800 CF of air assuming 8 foot ceiling (a little more if you have some vaulted ceilings like I do). So if a stove consumes 10 CFM of air per minute, it would take about 10 hours to consume the air in a home. Or put another way, the air would have to seep back into the house to replace itself every 10 hours or so. Then you have the issue of if you ever open any doors.

In my opinion, the lack of scientific evidence or evidence based data is a major flaw of the article. It's all conjecture. There was also an assertion (at least it was interpretation), that because EPA certified stoves are more "efficient" they consume less air. I would submit they require they require roughly the same amount of air to combust the fuel, the difference is how much heat goes into the space it's heating, instead of up the chimney.

I think you are on the right track.

Heck a bathroom vent fan probably sucks out 3 or 4 times the amount of air compared to a wood stove..for sure a cat stove on low cruise.

Until someone can show me a vid ..some test where they got a stove without a oak to spill smoke out the intake..I call bull.
You can run all the dryers and exhaust vents all you want in the vid I speak of..I doubt you can do it.

I have had 3 bath vents on..range vent ..clothes dryer,while burning wood...all was fine.
2500sf house..fairly tight.
Maybe some super duper insulated house of 1,000sf..that would be like living in a thermos bottle...and would need a air handler..which kinda defeats the super duper insulation imo.

The size of the house is irrelevant* other than it a larger house is likely to have more infiltration because it has more outer surface area, and hence potential infiltration leakage points. As another poster pointed out, the danger is not that the oxygen is consumed. The danger is back-drafting/draft reversal.

As I wrote previously, it all comes down to the path of least resistance. As we tighten up our houses for energy efficiency the risk increases that combustion appliances contaminate our living space with carbon monoxide.

I'd suggest that your house may not be as tight as you think it is. I thought our was relatively tight too until we had an energy assessment performed that included a blower door test.

Edit: * house size (volume) is relevant if you're looking at the effect of the introduction of carbon monoxide as it affects concentrations in the air.

 

[semipro]

Tom Oyen has a couple good articles on this topic. Like a flue damper, the need varies depending on the installation and the state. In WA, OAKs are required for all new home installations. As fuel prices go up and people demand better construction techniques for insulation and sealing, houses get tighter. If there is insufficient make-up air, an OAK becomes necessity for some installations.

(broken link removed to http://www.chimneysweeponline.com/hooa.htm)
(broken link removed to http://www.chimneysweeponline.com/hooa3.htm)

Thanks for posting. There's some good information with real life experiences with contamination of indoor air by combustion appliances in tight houses.

 

[SKIN052]

Semipro, I agree then, if you live in the ultimate bubble, an Oak is must. Not to be snide but your argument is fixated in the fact that a super tight home is the ultimate goal. If that is the case then yes, you may need extra air if you are utilizing a wood burning appliance.

 

[HotCoals]

My house is tight enough to keep me happy.
Of course I agree with you..the bigger the house the more chance of air leaks.
But also the bigger the house the more initial air it has..only makes sense.
I bet our door to the outside gets opened 10 times a day at least...and the slider right next to the stove maybe as much..cats want in and out..in and out..lol.

 

[SKIN052]

only 10? You clearly do not have kids.....I estimate, 40 times at least.

 

[HotCoals]

There is way more science as to why you most likely will never need a OAK...it's hard for my little mind to figure it out.
Some say fire can create oxygen even..dunno...some say when your chimney is drafting some outside air is coming down the flu to help burn the fire..I don't know about that either.

 

[HotCoals]

I live in a new home built to code, 3 years old and tight as a drum in my opinion (but lets be reasonable). Two baths, kitchen vent, HVAC, 2650 sq/f, etc. Stove was installed 2 years ago and I have yet to notice the stove is robbing air from from the house. Where does the idea originate that a OAK is a must in new homes?

Rumor is it started years ago because of smaller mobile homes.
I guess they thought they were really tight..lol.
Furnaces in mobile homes must draw their combustion air from outside also.
Hot water heaters also.

 

[semipro]

Semipro, I agree then, if you live in the ultimate bubble, an Oak is must. Not to be snide but your argument is fixated in the fact that a super tight home is the ultimate goal. If that is the case then yes, you may need extra air if you are utilizing a wood burning appliance.

Well maybe not super tight. I'm personally shooting for about 3 Air changes per hour (ACH) on our house. This is measured as a standard with a 50 pascal difference in pressure between the outside and inside. Of course the actual infiltration will vary depending upon wind and other factors.

At 3 ACH there is general professional agreement that no additional introduction of fresh air from outside (by HRV, ERV or otherwise) is required to stay healthy.

I guess my fear is that someone is going to crank up their monster downdraft range hood while the dryer and bathroom vents are running and someone's going to get CO poisoning.

If nothing else, if folks don't want to run an OAK I would urge them to definitely use a good CO detector.

 

[stircrazy]

Interesting topic.

personaly I am using my ash clean out in the fire place as a pasive intake but I am thinking of sealing it off.

I had an energy audit done on my house a year ago to be able to get rebates and such for a new furnace and door.

there system using the air bladder test has been used in canada for a long time. I did the same thing for my older house 16 years ago.

anyways it is measured in cu ft (or cu meters) of air flow as a specific presure differentual. so they basicly suck air out of the house to put the house in a slight vacum (there is a specific number they use here but I can't remember) then measure the air flow through the fan.
then after I did my upgrades they do it again and give you a befor and after, I also got a energystar sticker with the rating of my house, which surprisingly scored very well for a 40 year old house.

now my question is, code for my house required an outside air make up plumbed directly into the furnace cold air intake. so I basicly have a 4" tube stabed into the side of my cold air intake comming directly from outside with no restrictions. I upgraded my furnace and hot water heater to direct vent with there own outside air, so do I still need to use the ash cleanout in the fireplace or will the cold aire return make up be enough?

Steve

 

[SKIN052]

I agreed completely then. If you are after the ultimate in HVAC science, then a CO detector is a must. Your points are just. Mind you I lived in Winnipeg with Natural Gas for a year and a CO detector was a must by the insurance company and highly recommended by most everyone. I awoke one Sunday morning and the mid level detector went off. Got everyone out called the gas company and waited 30 minutes for them to show. Only to say, nothing wrong here, that happens some times. I asked if I had bought a chepo detector, nope was the answer, that just happens, live with it.......

Gotta go with common sense most of the time....

 

[HotCoals]

I gots a Canary!

 

[Treacherous]

7 more pages of debate from '06

https://www.hearth.com/talk/threads/2496/

 

[semipro]

Interesting topic.

personaly I am using my ash clean out in the fire place as a pasive intake but I am thinking of sealing it off.

I had an energy audit done on my house a year ago to be able to get rebates and such for a new furnace and door.

there system using the air bladder test has been used in canada for a long time. I did the same thing for my older house 16 years ago.

anyways it is measured in cu ft (or cu meters) of air flow as a specific presure differentual. so they basicly suck air out of the house to put the house in a slight vacum (there is a specific number they use here but I can't remember) then measure the air flow through the fan.
then after I did my upgrades they do it again and give you a befor and after, I also got a energystar sticker with the rating of my house, which surprisingly scored very well for a 40 year old house.

now my question is, code for my house required an outside air make up plumbed directly into the furnace cold air intake. so I basicly have a 4" tube stabed into the side of my cold air intake comming directly from outside with no restrictions. I upgraded my furnace and hot water heater to direct vent with there own outside air, so do I still need to use the ash cleanout in the fireplace or will the cold aire return make up be enough?

Steve

What "cold aire" return are you referring to? I would think that one gauge of whether you need to continue to use your cleanout as an outside air source is whether you feel a lot of flow coming out of it while your insert is running (when its not windy outside). Of course you almost certainly can't get to the clean out with the insert installed.

 

[semipro]

7 more pages of debate from '06

https://www.hearth.com/talk/threads/2496/

Probably one of the most divisive and rehashed topics here.

I originally posted the link because I found some references to such things as "Saskatoon Loop" interesting. I'd never heard of a trap being used in an OAK to prevent infiltration when no make up is needed. The trap concept apparently doesn't work BTW.

 

[LLigetfa]

The trap concept apparently doesn't work BTW.

Since a direct connected dedicated OAK is a push/pull between the outside and the flue, the trap would be immaterial.

In my former home, code required a general make-up air vent for the home. It was essentially a 6 inch hole in the wall 4 feet up off the floor with a 6 foot length of insulated flex duct. With a 4 foot drop to the floor, the cold air would rush in and pool on the floor. If I raised it up closer to the ceiling, much less air flowed out of it. While the NPP would certainly have been a factor, cold air being heavy would cause it to pour out downhill easier than flow uphill.

 

[HotCoals]

As I recall there is a screen on the bottom of my stove where the OAK hooks in and I KNOW there is one on the outside.

I calculated that my 1600 SF house has about 12,800 CF of air assuming 8 foot ceiling (a little more if you have some vaulted ceilings like I do). So if a stove consumes 10 CFM of air per minute, it would take about 10 hours to consume the air in a home. Or put another way, the air would have to seep back into the house to replace itself every 10 hours or so. Then you have the issue of if you ever open any doors.

In my opinion, the lack of scientific evidence or evidence based data is a major flaw of the article. It's all conjecture. There was also an assertion (at least it was interpretation), that because EPA certified stoves are more "efficient" they consume less air. I would submit they require they require roughly the same amount of air to combust the fuel, the difference is how much heat goes into the space it's heating, instead of up the chimney.

That is truly a thought provoking statement...best in the thread for me.

For a cleaner burn the A/F must be in a certain range.
Newer stoves have more firebricks and some have double walls or shields,baffles or whatever in the box to try and keep temps up for a cleaner burn.
In you're opinion do you think that helps to keep the air flow down?

With my cat stove I hardly ever have flame once the stove is cruising. The cat gets really hot and cleans up the smoke(gasses).
Therefore the stove can burn clean at a low flow rate without the proper A/F that you would need for flame to clean up the burn is my thought.