'Outside Combustion Air'

i have a mag stoker connected to where my propane hot air furnace use to sit in the cellar. a 2" pvc line is still there to the outside (which is capped), which the furnace used for exhaust. I was considering using this outside air and connecting it to my combustion fan on the stoker.

are there benefits to this, as compared to using the room air...since the negative pressure of the fan is sucking in 'outside air' through cracks in the house anyway? it's not a big job to do, but is it worth it? i'm also concerned about 'condensation' when the zero degree incoming air hits the interior of a 400 degree stove.

does the extremely cold outside air supply make it harder for the stove to keep it's high core temp, without using more coal?

many questions---sorry. you folks have been so much help to me with this stove in the past few months.

thanks,
tom

Tom,
From what I understand it is better to use the pipe you have rather than sucking cold air through the cracks in your house. Remember you are trying to heat the house not draw more cold air in. I found on my Harman hand fed stove that when I brought in fresh air from outside the stove ran more efficiently. The cold dense air contains a higher concentration of oxygen to burn.
Tom

Tom, I added a fresh air intake on my Alaska stove about 3 months ago and its working well. I was concerned about condensation also, but at 0 degrees right now I checked and have no signs of moisture.
I added a 45 degree fitting turned downward and a fine screen to the outside end to keep rain, snow and critters out.
After adding the intake it seemed to improve the airflow thru the house.
One thing I did do was purposely kept a gap in one of the fittings in case the inlet would become blocked and the stove would be starving for air.
I say hook it up and keep an eye on it till your satisfied.

Tom you will really like using outside air, there are dozens of cracks, gaps etc in the average TIGHT house. HUndreds of gaps in my old farmhouse, aka THE SIEVE.

One thing to remember about condensation, it is warm moist air condensing on a cooler surface, [you get condensation on a cold glass of soda, not on a cup of coffee right? ] So bringing in cold outside air will not result in any condensation. The only possible place would be on the outside of the cold pipe or tube bringing in the outside air, and getting condensation on the outside of the pipe itself.

During the spring/summer/fall when the stove is shut down. You definitely want to close off the outside air, the warm/moist summer air will condense on the inside of the stove and cause rust and corrosion.

Take care, Greg L

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My experience is colder air always aids combutsion better and hotter than warm household air.

thanks to all of you for your quick responses & sharing your knowledge. I plan on running the pvc right up to the back of the stove and finishing the connection with flex s/s pipe if I can find it. I don't remember ever seeing any 2" flex pipe or plastic hose in my travels, but i'm sure someone makes it. here's a picture of where I terminated the pvc exhaust line & the drip line below it. once completed, i'll keep an eye out for condensation on the exterior of the pipe greg (ls farm), but it shouldn't be a problem even if there is some.

thanks again all,
tom

Tom you can find SS flex pipe at an autoparts store, but you may find it cheaper to use an adapter on the PVC to increase the size up to a dryer vent size hose. And that hose is cheap.

Don't restrict the air at the blower inlet, it pulls a lot more air through it's 2-3" diameter opening than it can pull down a long piece of PVC, Leave a gap in the connection at first and see if it is still pulling air from the house.

Greg L

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good idea greg. i'll check the amp draw on the motor before and after to see if it's struggling pulling air thru the pvc...once I locate the parts I need.

and I thought I was all done with this stove?

tom

Hi All, I thought the heating season was over, but not quite, yet.

I've got a question, which I don't see addressed anywhere in my site search.

For those of you , who have added an outside combustion air source: I'd like to know, how an "outside combustion air source" influences the indoor humidity? Not to ask, "Does it add humidity to the indoors?", but, "Does the outside air source preclude lowering the normal indoor humidity and prevent the indoors from becoming so dry during the heating season?"

During the heating season, I use about 5 gallons of water a day in the humidifier. If I don't use the humidifier, the indoor humidity drops to ?? 12% .. maybe less.

Hi Dallas, it's been a long time since I've seen a post from you.

The relative humidity of cold winter air is about the same as normal warm summer air, but when you heat the cold air, to comfortable temperatures,
it's 'relative humidity' is much lower.. the warm air can hold a lot more moisture, but it started out as cold air.. so there is less actual moisture.

Same situation up at altitude in an airplane, the cold, -50* air outside, when pulled inside the engine, compressed and heated, then pumped inside 'the
fuselage, it's very dry compared to how much moisture it could hold..

So I don't think using outside air for combustion air will have any effect on the relative humidity inside your house.
Somebody may have a different 'take' on your question ??

Hope you are well, good to see you back on the forum.

Greg L

Howdy Greg,
I don't disagree, but if the conditioned indoor air wasn't used for combustion, it would seem that the indoor humidity could remain higher. >> there wouldn't be so much dry air infiltration.

But wouldn't the humid indoor air have to be replaced by infiltration anyway?? any air going up the chimney has to be replaced by either infiltration or by a dedicated comustion air duct??

Maybe I'm missing something?

I have to run humidifieers in my house, and it doesn't have any significant infiltration, or air going up a chimney,, My coal boiler is in an outside
buiilding and hot water piped in to heat the house.. so my heated floors and baseboards are heating the ambient air, not any significant amount of
outside air is infiltrating..

Greg.

I don't use outdoor air supplies but here's my thoughts.

Greg is right about cold air holding less moisture than warm air. As cold air is drawn inside and warmed it can now hold more moisture. This warmed air has a drying effect on us giving us dry throat, skin etc. Even in air tight homes, air eventually leaks in and causes this drying process.

Maybe if you ran the supply directly to a stove less air would have to "leak" into the house to replace the air removed by chimney draft which cold lessen the low humidity issue....?

Were you thinking of running the air supply directly to the stove or just terminating it near the stove?

rockwood wrote: Were you thinking of running the air supply directly to the stove or just terminating it near the stove?

I have three outdoor combustion air sources ... one is a "can" by the furnace, which runs when the oil burner runs. Another is an outdoor source in the fireplace, for when I am burning it and the other is a pipe, with it's outlet near the coal stove. However, when tending the stove, I can feel the cool air coming across the floor to supply the stove. So, I was thinking about dumping the pipe's supply directly into the stove and pretty much eliminating all or most of the house air for stove combustion.

I was trying to get an idea of how much good this might do for the "whole house humidity".

AH, now I get it,, yes, it might work. the cold air with low humidiity is used for the stove instead of the house air that has had moisture added from your humidifiers.. Yep, a dedicated air source to feed the stove might reduce the loss of humid air.. worth a try..

But if I remember correctly, you have a hand fed stove with a slider air vent on the ashpan door? you will have to get creative to make a duct to feed the
ash pan door vents.. But I believe you are pretty good with sheet metal !!

Greg L