What boost in efficiency does using outside air give a wood stove?

[ptm01]

I have a friend who heats with his wood stove 24x7. When I am by the wood stove, I feel the heat, but also the draft of air on the floor traveling towards the wood stove. Isn't a wood stove, going to consume the Oxygen in the house , thereby creating a pressure drop, thereby pulling in cold air from the outside, through every small opening in the house?

Does putting in a direct air feed from the outside directly to the stove, boost heat production because the stove is not pulling in cold air into the entire house?

Thanks in advance for your answers.

-Peter

 

[bholler]

I have a friend who heats with his wood stove 24x7. When I am by the wood stove, I feel the heat, but also the draft of air on the floor traveling towards the wood stove. Isn't a wood stove, going to consume the Oxygen in the house , thereby creating a pressure drop, thereby pulling in cold air from the outside, through every small opening in the house?

Does putting in a direct air feed from the outside directly to the stove, boost heat production because the stove is not pulling in cold air into the entire house?

Thanks in advance for your answers.

-Peter

Yes it can increase the efficiency but honestly it depends allot upon the house in some it will help allot others it will really make no difference. In some houses that are sealed really well it is nessecary for the stove to work

 

[Das Jugghead]

Installing an outside intake on my stove made a huge difference in reducing the cold air running across my floors toward the stove. I have been on a mission to seal up the leaks in my house as the cold air coming in mixes with the inside air and makes heating the house an uphill battle.

 

[St. Coemgen]

I think others already addressed main issues (if the house is tight, then you need outside air, else, it won't matter). But also do consider that every wood stove works by both convection and radiation of heat. The amount of each depends on the stove. Or stoves heat mostly by convection (about 70%), so there is always going to be some air flow on the floor from other rooms, usually along the floor (but I have installed fans to move cold air to the stove in other ways). Just saying, cooler floor air movement may be an indicator of house leaks (and decreased efficiency), or simply part of the way it works.

Side note: I have outdoor air pipes to both our wood stoves, and still have normal floor level cooler air movements. Because again our stoves are designed to heat mostly by convection. In fact, here is a photo of the decorative air vents on the top of our stove for such convection (I think they are lovely ):

 

[electrathon]

There are two issues here. First is 100% of the air going up the chimney is offset by either air from an outside air inlet of by air leaking into the house (from suction) from any number of small leaks all over your house. Without an outside air source you are drawing cold air into your house and using already warmed air inside the house as "chimney air". It will always take more BTUs of energy to heat the cold outside air drawn into the remote places of your house than it does to leave the warm air in the house and use cold outside air a for the chimney discharge. There is some argument that people have so much heat from the stove that it does not matter, the opposing argument is why are you wasting heat, wood, BTUs when there is no need to.

Second is if your house is well built (minimal air leaks) your chimney will struggle for air. outside air will always help with that issue.

 

[Ludlow]

An air kit will diminish the amount of cold air infiltration in far rooms through windows and sill plates. Makes the far rooms temp warmer and less drafty. I say if you are able to run a correct air kit there is no downside no matter how old the house.

 

[Kevin Weis]

I have a 135 year old leaky house. Yes, it leaked plenty f air to feed the stove but that air still had to come from the cold air outside. So I still installed an outside air kit and it did make the room the stove was in noticeably less drafty but there was still a natural circulation cold air coming into the stove room low and warm air expiring the stove room higher up and into the main house. So to me still greatly beneficial.

 

[Highbeam]

The point is not that you need an outside air feed with a tighter home but that you can get away without one if your home is leaky enough. Everyone should have an outside air connection. It’s even required by code in many places including my county. I would have failed inspection without it.

In addition to efficiency loss, not using an OAK means sucking in all that dirty outside air that is very dry once heated so you have very low humidity too.

 

[St. Coemgen]

In addition to efficiency loss, not using an OAK means sucking in all that dirty outside air that is very dry once heated so you have very low humidity too.

Well that depends....

First, don't assume that "outside air" is dirty. Our country air is not for example.

Second, I would love more dry air flowing into our house. Our 100+ year old stone house has damp issues. The more dry air I can bring in, or easily heat to dry, the better.

That is, the world is complex. There is no "one" solution. One must adjust to local conditions and adapt accordingly.

 

[jetsam]

Imagine a part time burner with a tall flue. How many CFM does the stove pull when not burning but with the air shut down as much as possible? Does the operator even think to shut the air down when they're not using the stove?

Outside air is potentially a big deal in this common scenario, even though no (wood) burning is even happening.

 

[Smokepole]

The point is not that you need an outside air feed with a tighter home but that you can get away without one if your home is leaky enough. Everyone should have an outside air connection. It’s even required by code in many places including my county. I would have failed inspection without it.

In addition to efficiency loss, not using an OAK means sucking in all that dirty outside air that is very dry once heated so you have very low humidity too.

All due respect Highbeam,I was taught, in many homes the inside air is more
polluted than the outside air. It is healthier for us and better for the house
If we allow the house to breathe.

 

[Highbeam]

All due respect Highbeam,I was taught, in many homes the inside air is more
polluted than the outside air. It is healthier for us and better for the house
If we allow the house to breathe.

If this is true for your house then there are better ways to exchange fresh air than by not properly feeding a combustion appliance with outside air. Your stove is for heat.

Open a window for example. Something you can undo once you realize the mistake. The modern way to deal with stagnant indoor air from modern construction methods is with an ERV.

 

[Smokepole]

If this is true for your house then there are better ways to exchange fresh air than by not properly feeding a combustion appliance with outside air. Your stove is for heat.

Open a window for example. Something you can undo once you realize the mistake. The modern way to deal with stagnant indoor air from modern construction methods is with an ERV.

I live in a log house I built in 1978 ,I guess I don't need an ERV, to each his own.

 

[FPX Dude]

The cold you feel is just the natural air flow that is occurring as it returns to the stove.

 

[ptm01]

Thank you all for you informative replies. They were all very helpful. I can't believe it is going to be 2020 in just a week. All the best to you all in the new year.

 

[electrathon]

The cold you feel is just the natural air flow that is occurring as it returns to the stove.

Well, sort of... It is the natural flow of air moving twords the stove to offset the heated air moving away from the stove diluted by the 10 to 20 CFM of outside air drawn into the house by leaks and discharging warm air up the chimney. It is the 10-20 CFM of lost heat in the house that is what this discussion revolves around. If you have plenty of extra warm air from your stove and the farther areas of your house are toasty warm too, then this is truly a who cares issue. If your house is cold on the outer areas it really does not make a lot of sense to add cold outside air to those already cold areas.

 

[John Galt]

This is one of the topics that I've noticed is very divisive around here. I believe that is due to the subjective nature and that there is no definitive answer. The science of building started in the 70's and no one has been able to agree since. The goal has been to create tighter houses and eliminate all air infiltration but that created issues with rot and mold. Air must be introduced as air is evacuated (and moisture must be dealt with) it's as simple as that. Where that air comes from is the question that must be asked. OAK, HRV/ERV, an open window, or cracks in the building envelope will all provide air but relying on those cracks could cause problems with moisture rotting the sheathing or growing a mold colony. Warm moist air condenses when it hits cold air, and if that area cannot dry out it will eventually fail.

My last house was a log cabin where you could see daylight at the corners. There was plenty of air being pulled inside though getting out of bed when it was 34 F was challenging. As I sealed things up, I could see where the air was now getting pulled into the house since the easy access points were closed. Frost was forming around the windows and baseboards. The logs were able to dry out during the summer so there was no serious damage but a stick built house might have trapped all of that moisture inside the wall.

Houses are different. Climates are different. Burns are different. Some people will need an OAK, some will benefit from one, and some will not notice a difference. Everyone should think about where that air is coming from and decide if they are comfortable with how it's getting inside.

 

[Das Jugghead]

All:

Say what you will. Bringing 10 degree air inside the building envelope will bring the interior temperature down. Installing an outside air intake eliminates that aspect of the equation.

Yes the natural course of convection results in the cyclical air flow from cooler regions to warmer regions. This is not to be confused with the cooling of rooms (or the building envelope) through the course of air infiltration.

If you have endless wood to burn and can burn wide open and you don't have rooms chilled by incoming cold air then more power to you. If you have limited wood, a leaky building envelope, and limited BTU production then an outside air kit coupled with vigorous envelope sealing and insulation is in your best interests.

My two coppers for what they are or are not worth - to each his own.