Fresh Air Intake - worth doing even if it's not necessary?

[Chris_Up_North]

So I am finally figuring out how to use my new Castine. The home is really comfortable tonight, almost too warm, despite it being 25F with gusts up to 40 mph.

Because of the way my home is set up and owing to the Castine's convenient fresh air intake at the back of the stove, it wouldn't be too much trouble to hookup a very nice fresh air intake and one wouldn't be able to see it from the main(e) room where the stove sits. I'm not at all anything resembling an expert on wood stoves but I assumed the following:

- Outside air will be cooler, hence denser in oxygen levels, and drier. Combustion likes that
- I won't be syphoning warm air out of the home to support the fire when it is -20F outside and windy
- During gusty, windy weather I won't have to worry about the stove back-puffing out of the intake
- Intake tubes are Neat-O

Especially regarding that last point, would it be stupendously dumb to plumb in an intake when it is working seemingly fine the way it is? Any disadvantages to a cold air intake?

It would be roughly a 20' run to the outside. Glancing at the rear of the stove it seems the intake is around 2.5", so for that distance would one need to run a slightly larger diameter tube for at least a part of the run and then end it in whatever roughly 2.5" pipe for the last several feet to keep velocities up?

Don't be afraid to tell me that this isn't a very good idea and that I should leave it as it is. Thanks!

 

[Highbeam]

You forgot the most important item. Humidity. Burning inside air means you are sucking in that cold, dry, outside air into your home and drying it out. Your indoor humidity will drop to popcorn fart levels without OAK and your furniture, door jambs, hardwood floors, and sinuses will be much happier with more moisture.

No reason to keep velocities up in the tube. Unless your owner's manual specifies otherwise, you can use 3" the whole way.

True, nobody has ever been hurt by an OAK. They can only help.

 

[ailanthus]

I'm also a castine owner and I've been thinking about installing an OAK more and more each year. My main motivations are the humidity issue and also reducing floor level drafts in an older house.

The question I've always had is whether I can run the outside air intake through the floor directly behind the stove (i.e. through the hearthpad) - I would use intake air from the crawlspace which is far from airtight.

 

[Highbeam]

I'm also a castine owner and I've been thinking about installing an OAK more and more each year. My main motivations are the humidity issue and also reducing floor level drafts in an older house.

The question I've always had is whether I can run the outside air intake through the floor directly behind the stove (i.e. through the hearthpad) - I would use intake air from the crawlspace which is far from airtight.

Yes, that's what you do, go through the floor into the ventilated crawlspace. That is perfect since the you get some crawlspace ventilation and the intake is unaffected by wind or debris blocking the inlet.

Here's mine, goes right down into the crawlspace.

 

[ailanthus]

Yes, that's what you do, go through the floor into the ventilated crawlspace. That is perfect since the you get some crawlspace ventilation and the intake is unaffected by wind or debris blocking the inlet.

Here's mine, goes right down into the crawlspace.

Thanks for the great info - that's probably all I need to finally pull the trigger.

 

[Chris_Up_North]

All fantastic information, thanks!

Is there a particular type of 3" tube one should use? I'm going to be actually drilling a hole through the floor behind the hearth pad, right next to an existing hole where a copper pipe comes through. It will go into the basement and run about 12' to an insulated plate that will be shared with my GenTran plug.

Will sucking -20F air dramatically in the coldest weather change the operation of the stove?

Thanks again!

 

[Highbeam]

Dryer duct is the proper material, rigid is best but the semi rigid aluminum is second best if you need to make bends. All from the hardware store.

I honestly have never burned -20 degree F air. The air under your house will be warmer than outside air but even still, the fire is over 1000 degrees so dropping the combustion air from 70 to -20 isn't a big deal.

If your house is really wet (somebody boiling food) and the intake air is really cold, you may experience some condensation on the outside of the metal intake tube as you would on a can of soda from the fridge.

 

[Backwoods Savage]

On the OAK, we have had them and haven't had them. There are plusses and minuses to each. Some have had some problems with the OAK in high wind situations and we had some minor problems with it. We considered putting our present stove with an OAK but decided to not do it and see how the stove worked. Overall, I like it best without the OAK.

Another thing is, if it isn't broke, don't try to fix it!

As for humidity, that will always be a problem in the winter months; inside and out. We never noticed a difference in the humidity levels with the OAK but on the other hand, my wife likes to use her solar clothes dryer in the warmer weather but during the cold, she likes to dry the laundry near the stove. It dries fast and puts a huge amount of humidity into the house. The laundry seems to be spaced in such a way that we do not have humidity problems.

 

[TreeCo]

On the OAK, we have had them and haven't had them. There are plusses and minuses to each. Some have had some problems with the OAK in high wind situations and we had some minor problems with it. We considered putting our present stove with an OAK but decided to not do it and see how the stove worked. Overall, I like it best without the OAK.

Another thing is, if it isn't broke, don't try to fix it!

As for humidity, that will always be a problem in the winter months; inside and out. We never noticed a difference in the humidity levels with the OAK but on the other hand, my wife likes to use her solar clothes dryer in the warmer weather but during the cold, she likes to dry the laundry near the stove. It dries fast and puts a huge amount of humidity into the house. The laundry seems to be spaced in such a way that we do not have humidity problems.

Thirty five years of heating with wood here and no OAK for us. Have tried it in the past but feel it is mostly a waste.

 

[elmoleaf]

Been doing some research on this myself recently. Here's what I found:
1. Be wary of installing a oak if there is a possible direct ember path from your firebox into the air intake. A backpuff/downdraft could knock embers into the air tube and cause a fire.

2. OAKS are most useful when there is supertight home construction...meaning a house built recently with a specific envelope air leakage goal in mind (blower door tests). This type of house can have problem with stove drafting correctly if other appliances (dryer, kitchen vent etc) running at same time. There is also potential that stove could draw combustion air via other unsealed combustion flues (traditional gas or oil heat)...reverse draft down other flues.

3. It seemed unclear how much combustion air (CFM) is actually used by a stove. Articles I read suggested it was surprisingly low, and that since fresh air is always needed indoors anyway a stove wouldn't cause significant draftiness in typical construction. It seemed house sill plate leaks, stack effect from recessed cans in ceilings and other typical air leakage points do more to allow outside air in than what a stove draws.

4. The consensus seemed to be a wait and see approach.....install and run without one. If there are draft problems, an OAK is one of many possible solutions.

 

[Backwoods Savage]

Not so sure about an ember getting into the air tube. Never heard of anything like that. If it happened with an OAK, it would also happen without the OAK which would mean the ember would pop right out of the stove draft. The most benefit seems to come from less draft along the floors of the house and in situations where people are running dryers and exhaust fans in a real tight house.

 

[Sprinter]

OAKS are most useful when there is supertight home construction...

I think that's accurate. And why they are required for mobile home installations because they can often be very tightly constructed.

I tend to agree with the "if it ain't broke, don't fix it" school of thought in general. But try turning on all the fans in the house and run the clothes dryer. Take a look at the stove. If it seems to affect the draft, you will benefit from an OAK.

 

[Chris_Up_North]

Some good things to think about. A few bits about my situation, blow by blow:

1. I don't think that is the case. I was thinking of using think wall metal conduit an running it to a side of the home with very little wind. I live near the top of a small mountain in a bowled-out hollow below the top.

2.The home is pretty darn tight. High R-values and newer double pane gas filled windows. There is only one doorway to the outside and it is through one very thick insulated door and a very well sealed interior door (Mud room). No other flues in the home. If I crack a window the stove operates a bit differently. That being said it is working fine now.

3. When the air supply is wide open during startup, I could see at least 100 CFM being sucked through. All shut down, very likely less than 5 CFM. These are generalized guesses but I think they could have some merit.

4. It's a pretty tall insulated interior chimney. I thought at first I had some draft issues, but it ended up being me not knowing how to operate this stove when I first got it. I've been splitting some of my existing splits smaller and testing every piece that comes in the home so I know there isn't a single non-seasoned piece going in the stove. A bit time consuming but it always seems to perform great so I keep doing it.

At the end of the day I'm trying to wring as much efficiency out of the stove that I can. Every piece I don't burn means a piece of don't have to fell, buck, split, stack, cart and stack again. We burned 1.8 cord last year with the old stove which was a somewhat leaky old VC Resolute. Bear in mind it is a well-insulated, 2-story home with only 900 square feet. I think this winter will be worse than last as well. Something about the apple trees this year.

Thanks for all your help and input!

Been doing some research on this myself recently. Here's what I found:
1. Be wary of installing a oak if there is a possible direct ember path from your firebox into the air intake. A backpuff/downdraft could knock embers into the air tube and cause a fire.

2. OAKS are most useful when there is supertight home construction...meaning a house built recently with a specific envelope air leakage goal in mind (blower door tests). This type of house can have problem with stove drafting correctly if other appliances (dryer, kitchen vent etc) running at same time. There is also potential that stove could draw combustion air via other unsealed combustion flues (traditional gas or oil heat)...reverse draft down other flues.

3. It seemed unclear how much combustion air (CFM) is actually used by a stove. Articles I read suggested it was surprisingly low, and that since fresh air is always needed indoors anyway a stove wouldn't cause significant draftiness in typical construction. It seemed house sill plate leaks, stack effect from recessed cans in ceilings and other typical air leakage points do more to allow outside air in than what a stove draws.

4. The consensus seemed to be a wait and see approach.....install and run without one. If there are draft problems, an OAK is one of many possible solutions.

 

[Sprinter]

Based on your last post, I'd say go ahead and do it. A small tight house is a fit for an OAK. If you put it in the crawlspace you don't have to worry about wind getting into it.

 

[Oregon aloha]

I have been told not to draw air with an OAK further the your chimney is tall. Also you could get some condensation on the pipe going though your basement with that large of temp. difference. How tight is your basement? Why not just dropping your OAK into the basement and draw air from there instead of running it to the outside. That way your pulling the humidity out of the damper basement instead of you home.

 

[Chris_Up_North]

I would love to pull air from the basement and it would be a bit easier to pull off as well. My only concern is that it would lower the basement temperature to levels that would freeze some of the copper pipes down there. As it sits now, the pipe temperature via the IR thermometer read 34F on the coldest night last season (-18F). The basement isn't nearly as tight as the house so air would definitely come in and it would be great to pull moisture our of there as well.

Am I not thinking it through about the temperature or would drawing air from down there make it even colder in the winter?

Thanks!

I have been told not to draw air with an OAK further the your chimney is tall. Also you could get some condensation on the pipe going though your basement with that large of temp. difference. How tight is your basement? Why not just dropping your OAK into the basement and draw air from there instead of running it to the outside. That way your pulling the humidity out of the damper basement instead of you home.

 

[Oregon aloha]

That could be true (Pulling air into basement) but you would be pulling less cold air into the upstairs, making your living space easier to heat. You can leave a dripping faucet if your worried about a pipe freeze. It's been in the teens at night here and that's what we do. We don't have any frozen pipes from the unheated well house through to the house.

 

[Mightiestmike]

Yes, that's what you do, go through the floor into the ventilated crawlspace. That is perfect since the you get some crawlspace ventilation and the intake is unaffected by wind or debris blocking the inlet.

Here's mine, goes right down into the crawlspace.

I could easily install an OAK through to my crawlspace as well, it is far from Air tight.
However would I then risk sucking cold air into my crawlspace and freezing my pipes?

Cause other wise, I got to go down into the crawlspace and then through the dry-stack foundation and up through the dirt outside.

Or OAK through a window. put 2 2x6's across the window with insulation between them so the up down window is now "closed" but open 6" and then bore a hole through the 2x6's for the OAK. this would also look less nice, but wouldn't be terribly inconvenient as we don't really walk behind the wood stove.


EDIT: Hadn't finished reading this whole post, someone asked my exact question...
I got no copper in the basement, but WELL - IN and Septic Out.

 

[Isaac Carlson]

We use outside air. We installed it a few years ago and it is great. The stove burns a lot better with it.