Anyone retrofit a positive shutoff for an OAK?

[LLigetfa]

I installed an OAK for my RSF 11 years ago and being a fireplace, it is not accessible to retrofit a damper in-line. If/when I burn 24/7 I don't have any problem not being able to shut it off completely but in very cold weather, if there is no fire, I get frost forming on the metal manifold above the door and on the glass from the air wash system. RSF has a notch in the butterfly so it's not possible to shut down the air completely. My chimney is chased up through the interior so it drafts constantly.

The OAK is installed low, just above the sill plate. I have crawlspace access under the fireplace. I'm thinking of drilling a small hole at a downward angle through the sill plate, subfloor, and top plate of the foundation wall into the crawlspace using a long cable installer's drill bit. Then I will drill another hole beside the hearth down through the floor into the crawlspace and fish a choke cable through the holes to the outside. My OAK has a wedge shaped hood as shown below. I will cut a rectangle of metal to use as a damper, hinge it at the top, and connect the choke cable to the bottom. Maybe some closed cell peel-n-stick foam for a good seal, maybe not. I wonder if I should let a bit of air leak in just in case I forget to open it and light a fire.

 

[bjkjoseph]

they sell one for fresh air supply for boiler rooms,it uses a damper.

 

[Wet1]

I have the same vent exit, but with the flapper. I leave it closed during the off season and when the stove will be down for extended periods. While using the OAK, I manually hold the flapper open with a paper clamp (mine is very easy to get to). W/o a decent seal on the flap, it still leaks a little air (it's a dryer vent), but it still works pretty good to keep the bulk of the air movement down.

 

[Highbeam]

Perhaps intalling a proper HVAC butterfly damper in the line between the vent and the fireplace. You can even buy motorized dampers. If you were dealing with a 3" OAK tube then you could fit in a 3" waste valve like they use on RVs. It is a gate valve that can be operated via cable. I don't think I would mess with the outside vent. Too exposed.

Note that even though you shut the primary air off, or as close as you can with the notch in your butterly, that the secondary air supply is full throttle and shooting full throttle secondary air through the appliance. I assumed that the RSF is a non-cat fireplace.

 

[LLigetfa]

Sometime after I bought and installed my vent kit, the manufacturer realized the problem and came out with a version that had a manual flap on the outside. Had I known the problem at time of install, I would have rigged up something on the inside. The duct is behind drywall now and I'm not about to redo the drywall just to get at it.

The way my RSF is designed, it takes the air for the secondary burner tubes and for the air wash (primary) from the OAK/butterfly. There is the zipper (doghouse) that draws room air but it's quite small in comparison.

Where I have my OAK on the exterior of the house it isn't easily accessible so essentially I just want to put a flap similar to the redesigned vent and put a remote control on it. I think the choke cable would have enough internal resistance to hold the flap closed when the choke knob is pulled out. I was even considering slaving it to the butterfly air control lever so they would work in unison. The actual butterfly is controlled by a bi-metal thermostatic coil while the control just tugs at the coil.

The RSF I had in my former home had a much longer run of duct for the OAK so the air had a chance to warm up a bit before reaching the stove so I wasn't aware of the frosting issue.

 

[LLigetfa]

OK, I got everything cobbled together. Here are some pics.

Closed:

Open:

The control:

The crawlspace:

The end:

 

[semipro]

I'm going to want to do something like this for my new Oslo install. I have a similar setup. I like your approach; simple, inexpensive, dependable. It's given me some ideas...

Thanks for sharing.