Fireplace insert heat ducted to basement return air duct

[Craby]

Do you think it is a good idea to install a 3" duct from next to the fireplace insert to my return air duct in the basement?
Here are some pics of the fireplace insert & return air duct.

There is 3 ½” between the floor joist & insulated hot water pipe so I think I can install a 3” flex stubbed into the return air duct.

If I put a floor grill on the flex do you think I would have a problem with getting dirt/debris drawn into the return air duct? Do you think I should stub up above the wood floor w/ 3” duct & extend it over the stove so it draws from the hot air above, or would that not really make a difference? Maybe I could paint the duct above the floor black so it blends in.

It would be a really short run as the return air duct is directly below my hearth. I might need to damper it down to maintain draw from the rest of the house return air grills. I wonder if it would whistle or if I would hear the A/C fan thru the 3" duct. Maybe I could built a sheet metal plenum box that covers the 3" pipe above the insert that captures the heat across the entire length and muffles any sound.

Would the 3" pipe get so hot that where it goes thru the wood floor I would have to seal the penetration w/ fire caulk or provide an air gap between wood & metal?

What do you think?

 

[begreen]

I think this is a bad idea for several safety reasons and it is entirely against code. Also, a 3" pipe is not going to move much heat. With uninsulated ductwork the heat losses to the basement will exceed the very minor gain here.

What's the actual problem you are trying to solve with this rig, moving the heat? There are probably much safer ways to deal with it.

FYI, here's how Blaze King sees it:

WARNING​

IMPROPER ASSEMBLY AND/OR INSTALLATION OF YOUR BLAZE KING WOODSTOVE OR FAILURE TO
OPERATE IT ACCORDING TO THE GUIDELINES DETAILED IN THESE INSTRUCTIONS, WILL VOID THE STOVE
WARRANTY, CAN CAUSE A HOUSE OR CHIMNEY FIRE, AND MAY ENDANGER YOUR FAMILY. FOR YOUR
SAFETY, FOLLOW THE ASSEMBLY AND INSTALLATION INSTRUCTIONS CAREFULLY. CONTACT LOCAL
BUILDING, FIRE OFFICIALS OR THE AUTHORITY HAVING JURISDICTION ABOUT RESTRICTIONS AND
INSTALLATION INSPECTION IN YOUR AREA. PLEASE READ THIS ENTIRE MANUAL BEFORE YOU INSTALL
AND USE YOUR NEW STOVE.

 

[webby3650]

I'm pretty sure building codes don't allow return air to be drawn from the area around a wood burning appliance. In case of a fire, the return air duct would suck flames through out the structure. And that's a bad thing.

Even if you chose to do it, I really don't think that you will see any real benefit. Using a small box fan to force colder air into the room where the insert is would be much more effective. Have you tried using a fan?

 

[Craby]

I am trying to move the heat.

I contacted Chris at Blaze King about moving heat to the basement, and he mentioned an idea of using an IR gun to find the hottest spot along the ceiling in my stove room, add a grill up high at the hot spot w/ 3" duct in the wall to a fan in the basement controlled by a rheostat conveniently located in the stove room.
I was hoping to avoid cutting up the basement gyp ceiling, 1st floor gyp wall and 2x4 sole plate to install the duct. Also, I would need to find a location to mount the fan (above or below the basement gyp ceiling?), run power to it, and install a rheostat at the 1st floor wall.

I have a local mechanical sub that was brainstorming this install with me and thought the return air duct would be the simpler way to get the hot air distributed. I do see your concern about fire safety.

 

[Craby]

Have you tried using a fan?

I tried this last year and it worked for the 1st floor, but my wife did not like the basement temp difference. She's used to heating w/ forced air furnace that leaves alot less difference between floors.
BTW, I keep my A/C fan on 24/7.

 

[begreen]

Code says that any return grille needs to be at least 10' away from the insert/stove. Also, as long as the ductwork is uninsulated, it is going to lose more heat to then it's going to move unless the basement is already very warm.

Let's start from scratch. Can you post a sketch of the floorplan that shows where the fireplace is and where the colder areas are? How do you currently use the basement? Is it partly finished?

 

[webby3650]

A $15 fan does everything I need. It really evened out the temperature in my house.
I really think a 3" duct will not move enough air to do any good. It's way too small, if it was enough, I'm sure you would see it used in construction. The smallest I've ever seen on a supply or return is 6".

 

[Craby]

Code says that any return grille needs to be at least 10' away from the insert/stove. Also, as long as the ductwork is uninsulated, it is going to lose more heat to then it's going to move unless the basement is already very warm.

Let's start from scratch. Can you post a sketch of the floorplan that shows where the fireplace is and where the colder areas are? How do you currently use the basement? Is it partly finished?

Here is the layout of the 1st floor & basement. The 3rd page is the 1st floor w/ the basement walls overlaid as dashed lines. Sorry, it's a scanned PDF so I don't know how to convert it to JPEG. The fireplace insert is in the family room.

We use the basement for watching tv & guest bedrooms. It is totally finished. We have drop ACT ceiling in the basement rec room only. Everywhere else is hard ceiling and mechanical room has no ceiling.
Thanks.

 

[begreen]

Great, is there a basement apt there? If so, the best solution might be a smaller stove like a Woodstock Keystone down there. Warm air is going to want to go upward, not down.

 

[HeorgeH]

"If I put a floor grill on the flex do you think I would have a problem with getting dirt/debris drawn into the return air duct?"

I have a forced air furnace with a return directly above the furnace horizontal on the first floor flooring. Yes it will suck in a lot of dust dirt ext. I went to the home store and bought a washable furnace filter with a customizable frame size, discarded the frame and laid the filter material on the intake register held down by magnets. I have to clean it sometimes once a weak, Vacuuming it works well enough most of the time, but I do have to wash it once or twice a month. I replace the filter inside the furnace yearly, but it is basically still clean after a year. So I think you will need a filter, and have to maintain it regularly.

I personally think unless your interior flooring is insulated the temperature will equalize anyway especially if you leave interior doors open. In the olden days they had transoms over all interior doors, no need for ugly ducts or air filters ect. If you have to do it, a better idea would be to run a duct up the wall with an inlet near the ceiling, where the hot and clean air is. You could also bury the duct inside a wall. It may even be possible to locate an insulated duct on the exterior wall running from the basement to an upper floor. I have seen that on multistory buildings with ground floor restaurants.

Looking for a high tech idea, run a heat pipe::
https://en.wikipedia.org/wiki/Heat_pipe

 

[Craby]

Great, is there a basement apt there? If so, the best solution might be a smaller stove like a Woodstock Keystone down there. Warm air is going to want to go upward, not down.

I do not have a basement apartment. We had relatives living in the basement, but it is used only by us now.

We use it for watching tv which we do more of in the winter. It stayed pretty chilly down there last winter unless we were running a couple 1500 watt portable electric heaters in the rec room. That room takes so long to warm up that by the time we were done watching tv it was just staring to feel toasty. What I ended up doing was to leave both heaters on low 24/7 which seams unsafe to me.

My wife is not too excited about getting a second stove. I thought about replacing our natural gas furnace w/ a wood furnace, but that seems excessive, too costly, and too much to keep up with running two fires.

I tried the small fan at the end of the hall upstairs pointing at the stove room which made upstairs more uniform temp but we kept tripping over the fan or the cord. I then tried the fan at the bottom of the staircase pointing upstairs, but did not see much improvement and also still tripped on the fan.

 

[begreen]

It's understandable why the basement fan blowing upstairs didn't work. Hot air is not going to want to go down. On the main floor, if the fan worked, maybe there is a more permanent way of installing a fan that stays more out of the way?

The basement rec room is going to need its own heat source. This could be permanent electric baseboards, a natural gas stove or a separate zone (with it's own thermostat) off the natural gas furnace.