Outside Combustion Air...Additional Considerations

While I had always thought that Outside Combustion Air was a "Given"...
This link from woodheat.org gives me pause...
**Broken Link(s) Removed**

It seems to me that, all things being equal, outside air is desirable in an otherwise "correct" installation (No?)
After all, if the installation is compromised, in one of the ways illustrated, wouldn't we get a face full of ash when the door was opened? [Or maybe not as draft is increased] Anyway, it is more fuel for thought.

Bob A

RMA wrote:While I had always thought that Outside Combustion Air was a "Given"...
This link from woodheat.org gives me pause...
**Broken Link(s) Removed**

It seems to me that, all things being equal, outside air is desirable in an otherwise "correct" installation (No?)
After all, if the installation is compromised, in one of the ways illustrated, wouldn't we get a face full of ash when the door was opened? [Or maybe not as draft is increased] Anyway, it is more fuel for thought.

Bob A

Hi Bob,
Thanks for the info. I just checked those articles, and I think I am ok.
My FireplaceXtrordinaire has TWO combustion air inlets, one on each side of the house. This neutralizes the "Wind effect" which could reverse the flow of smoke from going up the chimney. Good design.

Also, my Harman DVC-500 has a DRAFT fan and a COMBUSTION fan. So outside fresh air is PULLED into the stove, then the exhaust is PUSHED out the chimney. "Wind effect" again, neutralized.

I guess its just depends on which stove you buy...

Chris F.

Do a search on here for Outside Combustion Air, some have piped the combustion blower up to outside air, depending on your stove you use, most are under a slight vacuum from the draft it creates up the chimney.

I can open the doors on mine without much ash coming out, when changing the pan or viewing the fire, of course some fumes may start coming out, since now you have broken vacuum on the stove and ,therefore, your draft will start to decrease.

I installed my new Alaska Channing not quite 3 weeks ago and love it! No problems using the pre-existing, previously abandoned oil furnace flue to an all brick exterior chimney (with fireplace above). My gas furnace uses PVC for the chimney.

I'm a little bit frustrated by the coal usage being too much, and suspect lousy coal from my dealer (they bag it themselves). But, in the process of elimination of other factors, I installed a combustion-air 4" PVC pipe from the nearest basement window to the bottom-of-the-protrusion combustion-air intake for the stove. The total run is about 25 feet with a slight downward tilt along the wall to promote cold air flow. Unfortunately, there was no other 'convenient' choices without boring a 4" hole in my front wall. But due to proximity of electrical and duct work, there'd be several bends in the pipe to go out the front wall.

The fresh air IMMEDIATELY produced a better, hotter burn!

Now...here's my question...

Should I connect the 4" PVC pipe directly to the stove, and it's 2.5" combustion air intake opening?

Due to my slight mismeasurement on a 64" piece of pipe at a 45 degree angle down to the stove, there's a slight upward pressure on the bottom of the combustion air intake if I install the final 90 degree elbow. Unfortunately, this makes the combustion fan a tad noisier...still quite tolerable (as it's in my basement), but still, of some concern. If I decide to keep the final turn up to the bottom of the stove, it will not be necessary to screw in anything. Of course, I also have a short left-over piece of PVC acting as a support from the floor.

But, for now, I left the final 90 off and end the pipe just below the combustion air intake.

Here's my reasoning...

Number one is that the combustion fan is probably designed to 'blow' rather than to have to 'suck' fresh air as well. While a fan is a fan is a fan, I have about 25' of piping with three, 45 degree bends and one 90 degree bend when it gets to the floor behind the stove (plus one more if I go directly into the inlet). Although there is a natural fresh air flow through the pipe, if I connect the final 90, the fan must do some degree of sucking, due to the length of the pipe and the uncertainty of sufficient air flow on a windless day. My concern is the extra 'load' on the fan would shorten the life of the motor, and, probably when it's 10 above outside.

Number two is related to number one...what if, by being connected, a sudden gust of air (today is very windy in Western MA) suddenly pushes TOO MUCH air into the combustion chamber. My thinking is this would be a 'closed system' from air intake (at the basement window) to the top of the chimney. A sudden, strong gust of air may simply blow my fire right into the ash box or right up the chimney! Either way, I could lose my fire, or, possibly blow hot (rice) coals where they shouldn't go. Yes, I have a baro-damper properly set to handle gusts, etc, but if it's literally being blown through the pipe from the outside, I can envision burning rice coal all over the place!

The reverse is also true...a downdraft through the chimney and a slight vacuum at the basement window. Although the fan would probably minimize or even prevent a 'back flow', I'm suspicious the possibility COULD happen.

Number three is why I chose NOT to connect it, but let the fan pull fresh air from 2" away...if the pipe doesn't provide ENOUGH air flow, then the intake fan can simply suck any additional air needed from the basement. Yes, it's a 4" pipe and a 2.5" intake on the stove. My concern is the length and the 4 bends in the pipe (plus final 90, if used) create a 'resistance' to the air flow...much like water pressure resistance limiting the flow if you 'crink' your garden hose a bit.

Any thoughts???