Q on air inlet for Kuuma VF 100

[motoguy]

We purchased our VF100 a year or so ago. We didn't have a chance to get the ductwork (ductboard/flex ducting) replaced before last heating season, so we didn't use/install the VF. We recently had all the ductboard/flex replaced with metal ducting (should be finished today), and installed the VF. I'm hoping to fire it up in the next day or two for a test burn, with cold weather starting to head into MO this weekend.

I've got a question on the air intake. I've read a lot of pro/con stuff about OAKs, and whether or not they are needed. My HVAC/ductwork installer suggested we may need one, as in his opinion "your home seems very tight". I have the VF installed at one end of our walk-out basement, against a concrete foundation wall. The VF is approx 12" off the wall, and the wall is approx 9' high. I had planned on installing an OAK just above the foundation wall, through the wood portion of the wall (and side of house).

I've attached pictures of the VF installation. Excuse the mess, as crap has been moved all around while they run new overhead duct runs. There will eventually be a wall installed, creating a dedicated furnace room for the VF, separating it from the rest of the living area. I've framed one wall into the room for interior access, and it will have an exterior door next year for outside access.

I'm curious about installing an OAK plumbed directly to the inlet damper of the furnace. It looks like it may be a bit of a PITA to get one around the metal damper box (with bleed holes and what not), but I'm sure it can be done. Seems that a direct-connection makes more sense to me than a "dump air into the room" setup.

I'm new to the wood furnace world, so I'd appreciate input and advice. The Kuuma is using the same chimney/flue used by the Avalon Arbor wood stove, which was in place when we purchased the home.

 

[JRHAWK9]

Good question. I've actually thought about doing this with mine, but don't know what, if any, benefit I would have. Our house is not air tight in any sense of the word. I do wonder where all the air is coming in from when the Kuuma, clothes drier and water heater are running at the same time. Then throw in the LP furnace if ever needed, there's a whole lot of air which needs to be pulled in from somewhere.

 

[STIHLY DAN]

Make up air is good and most likely needed, but to tie it into the inlet is a BAD idea. If you don't believe me contact Kuuma, they will say the same thing. You do not want cold air feeding the fire, thats why the intake is on the back rather than in front of the unit. The warmer the combustion air the better. So if you air making a furnace rm in a tight house you will want a 6 inch outside air ducted in a short u, as in 90 down to the floor then 2 90's put together and back up 6 or 7 ft topped with a T or 90. This will create a cold air trap and only allow air to flow in only when the rm is in a negative. This will also allow the air to warm a bit then mix with the warm air in the rm before being brought into the unit to burn.

 

[garmford]

Could you please explain what OAK's is?
I'm guessing it's some sort make up air system judging from the conversation.
My house has a fresh air intake as part of our Lp furnace. At the end of one of my return ducts there's about 20' of flex that goes to the skirt of the house. This will keep an equal pressure in the house if the bath fans, clothes dryer, Kuuma, or other things are running. With out make up air you could create negative pressure in your house that could also cause the draft in your chimney to stall or at least be very weak. Your house looks like it would be less than 20 years old. Not sure if it's code but I would think your house would have a fresh air make up too. Stihly may know if it's a code or not.

 

[STIHLY DAN]

Could you please explain what OAK's is?

outdoor air kit. Its a kit that feeds the appliance's combustion air directly from outside. This is fine with fossil fuels, but not good for wood.

 

[garmford]

Gotcha. Thanks for the explanation.

 

[motoguy]

Fired the Kuuma up for the first time tonight. So far, it's doing great. Heating our 4k sq ft house up to 71 so far, and it's been climbing ever since I fired it (5-5:30pm, at 64 degrees). I've got it set to max heat output, to see what it'll do. I just put in the 2nd load, and I'm curious to see how it does with it/if the temps keep climbing. Outside temps show 35 on my wireless temp display. I'd like to know we can rely solely on the Kuuma for heat this winter, even when it dips below 0 (which is pretty cold for us in central MO).

I definitely think I'm going to need to install a make up air path. Being curious, I cracked a window near the furnace. Wow. It felt like forced air was being blown in (which, I guess it was). Seems like the house temps climb faster with the window cracked open vs closed, which seems backward to me. I guess that's proof that the increase in air is more important than the cold air being drawn through the window.

I don't have return air ducting connected to the blower inlet on the Kuuma; it's in an open area and we're using an open stairwell as the return air from upstairs. The center of my barometric damper is located about 13.5" above the blower housing, parallel to the housing opening. Currently, the draft seems to be good, as the baro damper is swinging a bit. However, I'm concerned about the blower sucking air through the baro damper/flue. Having a make-up air kit would reduce this possibility, correct?

I've purchased some 6" ductwork and a wall intake. I'll be running this down the wall (within a couple feet of the furnace), making a U (or putting in a T, with one side plugged), then running back up 6 or 7 feet. I'll probably put another U on it there (exit to the bottom), to keep crap from falling down in the pipe.

I'd like to put in a backdraft device, to ensure there can be no "backward" airflow in the make up plumbing. I don't want warm air from the house being sucked out, or the air system somehow being reversed in the furnace. Are there any recommendations on a particular brand/make/model of 6" backdraft damper to use? Or is any one as good as the next?

 

[maple1]

I think the idea of the U & up & down in the OAK piping is to act as a 'checkvalve' or air trap - so it should serve somewhat at least as a backdraft device. I would likely run that setup & see how things act. It might look kind of odd, but you could then maybe throw a barometric damper on the end of it that should work as a backdraft device, as long as it is oriented right (would have to be backwards to its ordinary orientation) - if it seems there is a need for that after you see how it runs as-is. Think you can get just the baro guts & screw them into the end of a pipe. Just out loud thoughts....

 

[JRHAWK9]

I don't have return air ducting connected to the blower inlet on the Kuuma; it's in an open area and we're using an open stairwell as the return air from upstairs.

If you don't plan on tying into your existing cold air system, I'd recommend putting a plenum on the cold air and run it up to near the ceiling of your basement. This will pull in the warmer air and not the cold stuff off the basement floor. I know all homes are different, but doing so with mine made a noticeable difference.

 

[motoguy]

If you don't plan on tying into your existing cold air system, I'd recommend putting a plenum on the cold air and run it up to near the ceiling of your basement. This will pull in the warmer air and not the cold stuff off the basement floor. I know all homes are different, but doing so with mine made a noticeable difference.

I won't be tying into the existing system, but I had planned on adding a plenum and running the pickup source away from the barometric damper a bit. My HVAC guy had suggested that I mount the inlet low on the ground, specifically to pick up the cold air (suck up the cold air, heat it, and bring it back in to cycle everything). Your suggestion (start with warmer air, end with warmer air) makes sense. Our basement is a partially finished walk out basement, so it's included in the living quarters. That being said, the floor doesn't get particularly chilly, either.

I think the Kuuma is already sketchy, regarding it's ability to keep the house warm in cold weather (4k sq ft home). The primary living quarters are upstairs, so heat up there is my priority. As such, I'll probably give your suggestion a try, in an attempt to keep the bedrooms and living areas warmest. Not to mention, running the plenum high makes it much easier to get around the furnace. Thanks!

 

[maple1]

That's a lot of home to heat. But likely about where we'd be if we our basement were finished & heated, though. You'll likely be pushing it's limits for sure.

 

[JRHAWK9]

I won't be tying into the existing system, but I had planned on adding a plenum and running the pickup source away from the barometric damper a bit. My HVAC guy had suggested that I mount the inlet low on the ground, specifically to pick up the cold air (suck up the cold air, heat it, and bring it back in to cycle everything). Your suggestion (start with warmer air, end with warmer air) makes sense. Our basement is a partially finished walk out basement, so it's included in the living quarters. That being said, the floor doesn't get particularly chilly, either.

I think the Kuuma is already sketchy, regarding it's ability to keep the house warm in cold weather (4k sq ft home). The primary living quarters are upstairs, so heat up there is my priority. As such, I'll probably give your suggestion a try, in an attempt to keep the bedrooms and living areas warmest. Not to mention, running the plenum high makes it much easier to get around the furnace. Thanks!

When I did this to mine (as well as mix in some of the radiant heat off the face), I didn't know for sure if this would then cause the basement to be too cold. Turned out it did cool it down a bit, but not a whole heck of a lot. My basement temps, at least where the furnaces are, pretty much stay the same temp as the rest of the house. I don't keep any supply vents open down the basement. The return air entering the blower box stays anywhere from 5-15° warmer than the basement/house temps, depending on where in the burn cycle it is.