Anatomy of an O.A.K. Install

[MisterFixIT]

After 8 years of burning wood and putting in a new wood stove I have finally gotten tired of having cold feet. The wood stove sucks in air from all the cracks around the windows in the back rooms and it tumbles down the wall to the floor and races across the floor down the hallway before finally getting burned up in the stove.
Along the way across the floor this super cold air chills the well insulated floor. The more wood I burn the colder my feet get. Cold feet makes all of me feel cold. The great irony of wood heat.

The rarely used furnace burns outside air and does not cause this effect so I thought why not give it a shot and install an Outside Air Kit for Mr. WoodEater.

Part 1: Planning: Gotta remember the 6P rule.

Have a picture of a wall before the sheet rock goes up is invaluable for planning and avoiding nasty things like live electrical wires. Looking at the picture the spot to the right of the outlet is almost a straight shot from the back of the stove to the wall. The spacing between the wall studs might give me grief but it rapidly becomes my Plan A. Plan B is somewhere just to the left of the outlet. It's doable but would require more bends in the pipe to connect the stove to the wall.

I decide that I want to route the pipe down to the vented crawlspace instead of going directly out the wall. I am unsure how my windy location would affect the air flow and would much rather burn 50F air from the crawl space rather than freezing cold 10F outside air.

 

[MisterFixIT]

Part 2: Exploratory Surgery: Is it tight? Why yes ... yes it is.

Vibrating multi-tools are great for cutting nice clean tidy holes in dry wall. They are also great for cutting off the nasty nails that like to poke at me.
Once that's done I conclude that my 4" single wall pipe has a nice snug 1/4" of gap on either side of the pipe. Perfect!



The only thing that can mess me up now are the floor joists that I can see in the crawlspace. I really don't want to cut a huge hole in the floor joists right where they sit on the foundation wall. I measure things a bunch of times but have a hard time figuring out where I am at in that regard.
So I drill a couple of holes, poke a couple short pieces of wire through and go check out where they end up under the floor.



They just miss the floor joists. I am so lucky!

 

[Sprinter]

I decide that I want to route the pipe down to the vented crawlspace instead of going directly out the wall.

That seems to be the most common way to go. It provides a sheltered air supply and works well and is the simplest approach as you have determined. It's what I did and works fine.

In my case, the space under the stove is large enough that it makes it easy to miss joists.

 

[MisterFixIT]

Part 3: Its hole cuttin' time!

Well almost ... Besides obliterating floor joists I am wary of cutting through almost the entire bottom wall plate that the wall joists rest on. Not sure what exactly that would do the structural integrity of the wall.

On closer inspection I figure out that I can probably bypass most of the bottom wall plate by angling the 4" pipe underneath my raised hearth instead of going straight down. Yay!

So enough planning ... my hole cuttin' finger is gettin' twitchy.

A 5" hole saw on the cordless drill makes quick work of the plywood floor. Reciprocating saw cleans up the other stuff in the way. At this point I'm like a day ahead of where I thought I would be on this project.

 

[MisterFixIT]

That seems to be the most common way to go. It provides a sheltered air supply and works well and is the simplest approach as you have determined. It's what I did and works fine.

In my case, the space under the stove is large enough that it makes it easy to miss joists.

When I was researching on this forum I read a lot of people doing the crawl space air come straight up through the floor. Not an option for me. There is no way im drilling the granite slab. I looked in my tool box but could not find the 4.5" diamond coated drill bit.

 

[MisterFixIT]

Parts 4 & 5: Its pipe makin' and pipe stuffing time.

I used three 90 degree elbows and a straight piece from Home Depot. They also sell a small sheet of metal with a perfect 4" hole in it. It was like they knew I needed exactly that when the decided to stock that part. It fit over the crimped end to make kinda like a wall flange.

Working with sheet metal is fun but I always forget to wear gloves and cut the heck out of my hands. Remember to wear gloves next time MisterFixIT.

I love metal tape. I love it so much I wrap it around and around and around. I put it everywhere. Even blocking off the bottom floor in the crawlspace. I am nuts when it comes to metal tape. Did I tell you I like metal tape?

A 4 x 6 reducer with some 1/4 inch mesh is great for keeping out the big monster insects that live downstairs. I might put in some finer mesh if I have issues after wood burning season.

 

[Sprinter]

When I was researching on this forum I read a lot of people doing the crawl space air come straight up through the floor. Not an option for me. There is no way im drilling the granite slab. I looked in my tool box but could not find the 4.5" diamond coated drill bit.

Well, granite would be a challenge I guess... I just had porelain tiles that I had to break up. It wasn't pretty, but it's all under the stove anyway...

 

[MisterFixIT]

Part 6: Let's put a damper on this thing:

No piece of ducting is complete without a damper. Why have one? Maybe ants will decide to make the pipe into an ant super highway! Maybe Mrs Black Widdy that lives downstairs might eat through the galvanized pure steel mesh and come up to say high. Who knows what could happen. Best to have a damper just in case. I suppose I might want to close up this thing in the summer to keep the air from whistling through it.

They make small dampers but not one that is air tight. There are gaps around the edges. So it fabrication time.
A piece of pipe, 4" damper, rope gasket, hot glue gun, couple of nuts and washers and presto ... insta-damper-adapter.

 

[MisterFixIT]

Part 7: Final Connection and Foam Filling.

A section of 4 inch diameter semi-rigid aluminium duct fits nicely between the damper-adapter and the PE O.A.K. adapter. You can see how the adapter offsets the rear venting hole to get under the blower (last picture).

Foam in a can is great for reinsulating the wall that had the blown in fiber glass. I'm glad I taped the hell out of the pipe and under the floor. The foam squeezes out of every nook and cranny as it dries and it would be a nightmare to scrape it out of the interior of the ducting. The multi-tool worked great to trim the foam flush to the wall. Now it's ready for drywall

 

[MisterFixIT]

Part 8: Warm Feet.

So now when I fire up Mr WoodEater and sit on the floor in front of it I still have air rushing past me towards the stove. This happens even if the blower is off.

But there is a huge difference. With the O.A.K. the air rushing across it is warmer than the floor rather than colder than the floor as was the case pre-O.A.K.

The air flow dynamics are now totally different: The air around the stove gets hot and rises. It moves up to the ceiling and across it flowing down the opposite wall. The warm air hits the floor and races across it toward the wood stove without entering it and getting burned inside it. The convective flow gets warmer and warmer, heating the air in the room as well as the floor.



Many thanks to Tom Oyen at ChimneySweepOnline for his help picking out the stove and the O.A.K. recommendation. Helped me out a lot!

 

[DBoon]

Did nearly the same and ducted the air supply from my unfinished basement. This created a negative pressure in the basement that caused radon levels to rise. Radon levels in the basement then tested at 17 pc/l, which required some remediation to get them back to <1 pc/l. So invest $20 or so in radon test kit and check out the radon levels in your crawlspace.

 

[MisterFixIT]

Did nearly the same and ducted the air supply from my unfinished basement. This created a negative pressure in the basement that caused radon levels to rise. Radon levels in the basement then tested at 17 pc/l, which required some remediation to get them back to <1 pc/l. So invest $20 or so in radon test kit and check out the radon levels in your crawlspace.

Excellent advise DBoon. Not just for people looking at O.A.K. install but for anyone looking at installing any kind of burning appliance in their living space. The air flow dynamics will change.

Think about what happens if you have high radon in a crawlspace and then start burning wood or pellets in your living room. Without an O.A.K., cold outside air gets sucked in through windows, doors and other cracks but it also gets sucked in from the high-radon crawlspace increasing radon infiltration from the lower level. Mabye the increased airflow from the outside dilutes the radon concentration or maybe it doesn't. It depends on the ratio of outside cracks vs crawlspace air leaks of the particular dwelling. Either way the radon poisoned air gets pulled through the living space and the inhabitants lungs before getting burned in the appliance and going up the chimney.

My non-inhabited crawl space has about 3 square feet of side venting so there isn't any way negative pressure is going to build up versus the outside environment. In my case there is no negative pressure that will pull the radon out of the ground. My O.A.K. if anything, reduces the potential for radon infiltration into the living area because the wood stove is no longer sucking crawlspace air through the living space. Also the crawlspace vented O.A.K. increases the air turn over in the crawlspace when the wood stove is burning. Additional air gets sucked in the crawlspace side vents which is then sucked through the O.A.K. ducting to the stove and then goes up the chimney. This helps dilute any radon that may make it past the thick plastic vapor barrier installed on top of the dirt crawlspace floor.

Below ground (sunken basement) or next-to-ground (slab foundation) dwelling areas are of particular concern when it comes to radon issues. I have never seen a finished or unfinished basement with massive amounts of venting to the outside air. I agree, any kind of negative pressure would increase the radon infiltration from the soil directly into a non vented basement. Combustion air from an attic space or direct to the outside would probably better in a radon situation. Did you take a reading when the wood stove wasn't burning for comparison sake?

 

[DBoon]

Did you take a reading when the wood stove wasn't burning for comparison sake?

I had tested it years ago and I recalled it was right on the bubble - 4 pc/l or so. I didn't test again without the stove running - didn't really see the point. Probably should have remediated at 4 pc/l anyways, and 17 didn't make me want to wait any longer.

 

[fire_man]

I'm glad it worked out for the OP installing and OAK. This article does not mention cold drafts without and OAK but basically says adding one is not helpful. Real world experience counts more in my opinion.

http://www.woodheat.org/the-outdoor-air-myth-exposed.html