Fresh Air intake Recommendation

[Cavalier]

I'm replacing my wood burner with the Propel PPC90 pellet stove. I know Propel is suggesting to install the 2" fresh air intake. However I'm wondering if I really need it. My cabin was built in 2008 so it is fairly tight however I do have a HVAC system that is both airconditioning and gas heating system. What recommendation do I get on this forum.
Thanks

 

[tlc1976]

There are many debates here on it but I think it is beneficial to always have it. Having the outside air kit (OAK) makes the stove run in a closed system. If the fire goes out the smoke goes back outside. It pulls combustion air right from outside. Without the OAK, the stove pulls combustion air from the house and that air needs to be replaced. So it pulls cold air in from any drafty window, etc. it can find. This explains why both houses where I burned wood, the back bedrooms were always so cold. The OAK is also easier to install while you're installing the stove to begin with.

If you burned wood successfully it's probably fine, but I found that even my 30+ year old house wouldn't run the pellet stove without the OAK. It was still too airtight.

 

[johneh]

I use an OAK only because I hated the fact I was
using heated air to supply the fire which I paid to heat!

 

[Overfireinthehole]

Does the fresh air outlet on your stove connect directly to your firebox, or is it just a hole in the back shroud? Also, what kind of insulation does your house have and what’s your elevation?

 

[johneh]

Does the fresh air outlet on your stove connect directly to your firebox, or is it just a hole in the back shroud? Also, what kind of insulation does your house have and what’s your elevation

Right to the firebox

 

[Overfireinthehole]

What you have to look at is how tight your house is. I have never seen a pellet stove who’s blowers had enough CFM to create leaks in a house. All houses naturally pull in fresh air from the outside, so the only Times that you have to have fresh air is if your house is breathing so little that your fire is not getting enough oxygen or if your manufacture requires it. People tend to think that a pellet stove will pour cold air in through windows and doors and walls, but I have yet to ever see evidence of this and I have compared a lot of stoves with and without OAK using a thermal gun. If you put a stove in in the back rooms of your house are still cold, it’s because the heat is not getting moved to that part of the house not because cold air is being drawn in from those rooms. Be aware, that an oakcan cause condensation issues and subsequent rust issues with your stove so you really don’t want one unless you have to have it.

 

[jerrieric]

I use an oak because when I didn't and the power went out smoke came back in the house. Not a problem with an oak

 

[FirepotPete]

What you have to look at is how tight your house is. I have never seen a pellet stove who’s blowers had enough CFM to create leaks in a house. All houses naturally pull in fresh air from the outside, so the only Times that you have to have fresh air is if your house is breathing so little that your fire is not getting enough oxygen or if your manufacture requires it. People tend to think that a pellet stove will pour cold air in through windows and doors and walls, but I have yet to ever see evidence of this and I have compared a lot of stoves with and without OAK using a thermal gun. If you put a stove in in the back rooms of your house are still cold, it’s because the heat is not getting moved to that part of the house not because cold air is being drawn in from those rooms. Be aware, that an oakcan cause condensation issues and subsequent rust issues with your stove so you really don’t want one unless you have to have it.

I'm sorry but it is basic physics, differential pressure, that is the reason to use an OAK/FAK.

I can find exhaust blowers in the range of 70cfm-120cfm in general. 70cfm =4200cfh, that's a large amount of air in one hour to suck into a building. To deny that it comes from outside is, again, against the laws of physics.

Measuring with a thermal gun is not going to show you the ambient air temp, you are measuring surface temp and will not see a large difference. Measuring they way you describe is the same as saying that you are measuring the surface area of a windshield when it is 0°F and it shows 0°F but the wind is blowing and the real feel is closer to -10°F.

I also notice that most people that say an OAK is not needed seem to live in areas that I consider to be warm compared to where I live, perhaps that is the difference in attitude. I also see people saying you only need it if your house is extremely tight. That is wrong also, any air being brought into the house from outside is going to cool the air that you are trying to heat, you might as well leave a window open.

I've worked with manometers and differential pressure transmitters for over 30 years and I can tell you that the science behind using an OAK is solid.

As far as added rust, I've never seen that because of an OAK install. Yes you can get extra condensation around the pipe while running, but that is easily dealt with. Also if the stove is properly maintained for shut down season there is no problem with moisture in the stove.

 

[Highbeam]

I'm sorry but it is basic physics, differential pressure, that is the reason to use an OAK/FAK.

I can find exhaust blowers in the range of 70cfm-120cfm in general. 70cfm =4200cfh, that's a large amount of air in one hour to suck into a building. To deny that it comes from outside is, again, against the laws of physics.

Measuring with a thermal gun is not going to show you the ambient air temp, you are measuring surface temp and will not see a large difference. Measuring they way you describe is the same as saying that you are measuring the surface area of a windshield when it is 0°F and it shows 0°F but the wind is blowing and the real feel is closer to -10°F.

I also notice that most people that say an OAK is not needed seem to live in areas that I consider to be warm compared to where I live, perhaps that is the difference in attitude. I also see people saying you only need it if your house is extremely tight. That is wrong also, any air being brought into the house from outside is going to cool the air that you are trying to heat, you might as well leave a window open.

I've worked with manometers and differential pressure transmitters for over 30 years and I can tell you that the science behind using an OAK is solid.

As far as added rust, I've never seen that because of an OAK install. Yes you can get extra condensation around the pipe while running, but that is easily dealt with. Also if the stove is properly maintained for shut down season there is no problem with moisture in the stove.

I agree and an OAK is often required by law.

One additional point is air quality. Not just dirt and pollen but bringing in all of that cold outside air and then heating it will drop the humidity like crazy. You want some air exchange but not this much!

 

[stovelark]

Plus one for OAKs. If you can, do it.

 

[Lordtimothy200]

Personally OAK is the best bet. However it is not always possible. I had to switch to inside air due to wind direction and speed. If we had a north wind over 25mph it would keep kicking in the safety off switch. Tried EVERYTHING but couldn't get it to work, so just went to inside air and life has be perfect..........well in the stove department anyway. I would do the OAK if you can.

 

[Overfireinthehole]

I'm sorry but it is basic physics, differential pressure, that is the reason to use an OAK/FAK.

I can find exhaust blowers in the range of 70cfm-120cfm in general. 70cfm =4200cfh, that's a large amount of air in one hour to suck into a building. To deny that it comes from outside is, again, against the laws of physics.

Measuring with a thermal gun is not going to show you the ambient air temp, you are measuring surface temp and will not see a large difference. Measuring they way you describe is the same as saying that you are measuring the surface area of a windshield when it is 0°F and it shows 0°F but the wind is blowing and the real feel is closer to -10°F.

I also notice that most people that say an OAK is not needed seem to live in areas that I consider to be warm compared to where I live, perhaps that is the difference in attitude. I also see people saying you only need it if your house is extremely tight. That is wrong also, any air being brought into the house from outside is going to cool the air that you are trying to heat, you might as well leave a window open.

I've worked with manometers and differential pressure transmitters for over 30 years and I can tell you that the science behind using an OAK is solid.

As far as added rust, I've never seen that because of an OAK install. Yes you can get extra condensation around the pipe while running, but that is easily dealt with. Also if the stove is properly maintained for shut down season there is no problem with moisture in the stove.

You hit the nail on the head. Geography is a big factor. If we get below 0dgf 5 times in one year it’s considered unusually cold. Accordingly, most houses are not built very tightly. I understand the science behind it, but I’m not saying it’s impossible for a stove to suck cold air into a house. I’m saying, the amount of cold air being sucked into a house already due to the house not being especially tight is enough to run the stove, and that the stove going to have a negligible impact on that amount of air. We get weeks on end of 80-90% humidity here, so very few houses are built tight enough for oak to be a necessity because if you go too tight you end up with mold and mildew problems. Also, the rust happens because the stove is circulating humid air all summer and because during burn season, condensation develops on the oak.

 

[Overfireinthehole]

Also, pointing a laser thermometer at a window would be idiotic. I’m talking about mapping airway in a building with a thermal imager like what I also use in house fires on my fire department. If codes or manufacturers call for oak then use it and if you think oak is better use it, but there is merit to the idea that you should try not using it if you can because it’s not always necessary and can create headaches for customers, especially if the oak hookup is just a hole that points the cold air in the general direction of the firebox.

 

[bogieb]

Do you "need" an OAK, probably not (unless legally required, like in a trailer), but you may "want" one. Again, as others have stated, it probably depends on how cold it gets outside as to what will be comfortable. When the outside temperature is in negative digits at night, and single digits during the day, for weeks on end, and my stoves are on continuously, they can draw copious amounts of very cold air into the house. With OAKs hooked up, that amount is drastically reduced.

 

[FirepotPete]

Also, pointing a laser thermometer at a window would be idiotic. I’m talking about mapping airway in a building with a thermal imager like what I also use in house fires on my fire department. If codes or manufacturers call for oak then use it and if you think oak is better use it, but there is merit to the idea that you should try not using it if you can because it’s not always necessary and can create headaches for customers, especially if the oak hookup is just a hole that points the cold air in the general direction of the firebox.

I didn't come up with using a thermal gun, you said you used it in post #6 above.

Without having to get into Pascal units, or measuring barometric pressure in inHG here's the rub on your thinking about a house having enough air already coming into it so an OAK isn't needed.

If a house has an air loss of say 5cfm naturally and then you create a vacuum of another 70cfm you now have a net loss of 75cfm. See it's not that you have enough natural air loss to run the stove, what you have is enough gaps where outside air can infiltrate and replace the air created by the vacuum.

If the house doesn't quite allow enough air to the fire then the stove will not run as efficiently as the design allows.

Also consider that you have a room that is 10'x10' by 7' high, that is 700cf. So if you have an exhaust blower running at 70cfm you are drawing out 1/10th of that total room air volume every minute or the total air volume every 10 minutes. That means without the OAK you air replacing that total volume of air of the entire room 6 times every hour. That's a lot of cold air coming in to try and heat.

Now turn on a bathroom vent fan for 20 minutes or a range hood vent fan, or a clothes dryer and the total air loss and cold air needing to be replaced is multiplied.

Consider forced air heating systems. How did they get to over 90% efficiency? Mainly by creating a total closed system where the air used in the combustion chamber is brought in from outside instead of the older system of using inside air for combustion.

 

[Overfireinthehole]

How much cold air are you bringing into the house by piping it in with an oak? On some stoves (Heatilators, some of the old Breckwells, the quad classic bays and others) your just piping cold air to the stove not into a gasketed area, so when the stove is not running you can have a cold draft around the stove. Not to mention that you can have radiant cold from the oak line. I’ve seen oaks that had ice crystals forming around them when the unit was off. Technically you are right that cold air infiltration can be helped along by the blowers on the stove, but when we are talking about thousands of square foot it’s a very negligible amount. It’s not healthy to have a house so tight there is no exchange of inside and outside air. That has been my experience in the 150 mile radius that my company covers. That being said, I’d probably feel differently if I lived in the mountains or up north where subzero temps are more common.

 

[FirepotPete]

Technically you are right that cold air infiltration can be helped along by the blowers on the stove, but when we are talking about thousands of square foot it’s a very negligible amount.

A 2000sqft house with 7' ceilings would be 14000cf. Running a 70cfm exhaust fan the entire volume of air in that house would be replaced every 3.3 hours. That is not a negligible amount.

 

[Overfireinthehole]

I’m curious now, where are you getting this 70 cfm rating?

 

[FirepotPete]

I’m curious now, where are you getting this 70 cfm rating?

I've had to replace them myself and for friends. Typical ratings are from 70cfm to 120cfm. None lower, some higher, just an average.

Here a link to a replacement for a common, popular stove:

Englander 85 CFM Combustion Exhaust Blower for Englander Pellet Stoves PU-076002B - The Home Depot

The Englander 85 CFM Combustion Exhaust Blower fits Englander pellet stoves and provides forced air (negative draft) that keeps the flame burning, while allowing you to set your heat range to your desired

www.homedepot.com

Also, in my calculations of a 2000sqft house and the cubic footage. The actual displacement number of cubic feet of of air would be higher in actual use because of walls in the house. My numbers where basically making the house a pure empty box and calculating the cubic footage.

 

[Overfireinthehole]

Also, by your logic, if I were to run only the exhaust blower on my stove for about 3 hours all of the air in my house would be replaced. Ok, does that replacement of air necessarily correlate to a significant drop in temperature in my house? If your cfm numbers are right then what your saying about airflow makes since, but I’m still questioning your conclusion that pulling air into the house from all the cracks and crevices is going to have a significant impact on temperatures and pellet use. I mean, how often is the air in your ideal home being exchanged naturally, and why is it in the hundreds of stoves that I service every year that there seems to be no noticeable difference in how many pellets people with outside air kits burn vs those who don’t have them. I notice a distinct difference in the amount of rust which admittedly wouldn’t happen if customers capped off their vents and intakes for the summer, but most of my customers won’t do that no matter how many times I tell them to. Are you talking about a net difference of a few bags of pellets or a few pallets, because I have customers who burn1.5 ton without oak and customers who burn 4 ton with oak. Finally, one last thought. Your assuming that all the air of a home would be replaced by a unit drawing air into the home, but air will chose the path of least resistance, so in most cases wouldn’t that path be simply to the nearest weak spots, meaning that you may be replacing the air closest to the stove but not necessarily the entire house? I’d rather have a slightly cooler draft of air along the wall between my stove and nearest windows when I’m running the stove than have cold air coming from underneath my stove any time it’s not running( the fresh air port on cb1200s is just a hole in the floor of the back of the stove with the stove drawing combustion air from underneath the stove).

 

[Overfireinthehole]

I've had to replace them myself and for friends. Typical ratings are from 70cfm to 120cfm. None lower, some higher, just an average.

Here a link to a replacement for a common, popular stove:

Englander 85 CFM Combustion Exhaust Blower for Englander Pellet Stoves PU-076002B - The Home Depot

The Englander 85 CFM Combustion Exhaust Blower fits Englander pellet stoves and provides forced air (negative draft) that keeps the flame burning, while allowing you to set your heat range to your desired

www.homedepot.com

Also, in my calculations of a 2000sqft house and the cubic footage. The actual displacement number of cubic feet of of air would be higher in actual use because of walls in the house. My numbers where basically making the house a pure empty box and calculating the cubic footage.

Ya, I’ve probably replaced over a hundred exhaust blowers and never noticed a cfm rating. Usually they just list the electrical specs and rpms.

 

[FirepotPete]

Also, by your logic, if I were to run only the exhaust blower on my stove for about 3 hours all of the air in my house would be replaced. Ok, does that replacement of air necessarily correlate to a significant drop in temperature in my house?

Yes, if the air temp outside is lower than the inside temp. And that is assuming that the temp is not just a few °'s lower, as you will still get residual heat from interior walls for a period of time.

I mean, how often is the air in your ideal home being exchanged naturally, and why is it in the hundreds of stoves that I service every year that there seems to be no noticeable difference in how many pellets people with outside air kits burn vs those who don’t have them.

It doesn't matter how often the air is being replaced naturally when talking about the affect of creating a vacuum sucking in outside air. It does matter to the home owner freezing their feet off, but it doesn't matter to the subject of installing an OAK, or not installing one.

and why is it in the hundreds of stoves that I service every year that there seems to be no noticeable difference in how many pellets people with outside air kits burn vs those who don’t have them.

Probably because of the differences in construction, layout or what ever. Every house/building is different, you can't compare one to the other, nor are you around to see how the owner is running or maintaining their stove, or what they consider a comfortable level, every one is different.

Everyday for many years on this and different forums I see people with smaller houses that are newer than mine, that live in much warmer climates using 4-5 tons of pellets per season. On average I use 3 ton of corn every season. My house is not well insulated and I live in a somewhat cold area. Not as cold as I grew up in near the U.P. of Michigan, but still pretty cold.

I'm out for the night. 04:30 is coming early. Later.