Wood burning furnace in basement – improving efficiency

[UpstateNY]

Gentlemen (and ladies),

I have a 2 story house, primary heat is via a natural gas-fired furnace. The original owner installed a wood burning furnace in the basement (see the attached pic) and never used it. It does have the required separate flue and works well. The WB furnace is not connected to the existing NG ducts, it simply radiates heat into the basement and, in turn, the heat radiates up into the first floor of the house. The basement does have insulated walls so it gets quite hot when the WB furnace is running. I have an unlimited supply of free, dried, hardwood to burn.

I’d like to improve the efficiency of the WB furnace. I plan on installing sheet metal around 3 sides of the WB furnace (the top and 2 sides), the sheet metal would have a 1” air gap (or so) from the WB furnace surfaces. I would install a 6” round duct from the existing return air duct to the top piece of sheet-metal installed on the WB furnace to draw hot air from around the WB furnace. I’d also install an in-line 6” 240 CFM fan within the round duct to assist in hot air flow.

This arrangement would draw air around the WB furnace and into the return air ducts. Both the in-line fan and existing NG furnace blower would be controlled by the heat sensor installed on the WB furnace, so the fans turn on automatically when the WB furnace has wood burning in it. The NG furnace would turn on normally when additional heat was required as determined by the thermostat setting.

All the parts would amount to about $75.00 and a few hours of work by me.

I’m doing all of this because I don’t think passively radiating heat from the WB furnace in the basement and into the living space is efficient. I know that some of the heat is wasted by heating the basement walls, floors etc; and, the basement is essentially unusable by me when I’m burning wood as it gets too hot to work in.

Given the low cost of the project, do you think this project would be worthwhile? Do you see any safety issues ? Has anyone done anything like this ? Thoughts ?

Thanks.

Joe

 

[yeldogt]

So there is no duct work -- it's just s stove?

 

[UpstateNY]

Yes, it's just a free standing stove. My plan is to run ducting to it and use an in-line duct fan and the existing NG furnace fan to **** hot air from the external surface of the wood burning furnace / stove. Thus heat from the wood furnace would enter the house ducts and be circulated into the house.

 

[bannerd]

There must be a return in the basement? You could just punch a hole in the return, that way it's just moving the hot air up into the house (Forcing the air). I don't see an issue with this, the concept they have is the same it sounds like. Hot air rises and their theory with punching a hole in the floors is to allow that hot air up into living space.

My shop furnace is a dutch waste oil furnace and I fabricated a square box with exhaust tubes passing through. The furnace sits outside because it get pipping hot, but I run a small blow which forces the air through the pipes into some ducting and dumps it into the shop @ 110-130F. -20F days and it's 90F in the shop (30x40)

 

[TractorJeff]

My Dad did what you are describing for years with no issues other than as the wood burns down his fans kept running eventually making cold air come out of the ducts and occasionally when filling a cloud or two would come out the door spreading smoke smell and dust through the house.

 

[J king]

I did it years ago. I removed the end panel in the cold air return. The heat traveled thru that and you could turn blower on furnace to push air to other areas. Worked fine but some said it would overheat the gas furnaces fan. Never did. I have a single story so really didn't need to run the blower much tho..
Now have an outdoor wood stove.. sooo much cleaner!

 

[gungatim]

I have that EXACT (almost, see yours is missing the top box) same woodburner in my hunting shack. heats the entire home pretty well (just a 900 sq ft. rectangle ranch). it puts out serious heat, and mine has hookups (but not used) for water to circulate through it. I just have a small fan mounted behind it to blow and circulate the hot air. if yours has the water hookups you could add a radiator and blower to it in the duct.

if you wanted to make a blower for it, make sure the air intake on front (that box thing) doesn't get blocked or the draft interrupted from the fan, it needs fesh air fed through there once it's set to burn good and hot...

 

[Boilerhouse]

I can certainly appreciate how wood stoves create hot and cold spots in a house. I have no first hand experience with the sort of set up you mentioned, so feel free to take this with a grain of salt. Some years ago, an HVAC tech was in my basement quoting for a furnace install and I asked him about running an intake duct above the existing wood stove. My memory is that he said this was against code, as producing a negative draft in the vicinity of a combustion appliance was a no-no and there was a (very slight) possibility of CO fumes being drawn from the stove and spread throughout the house. So, if I were to consider a hook up as you described, I would probably want the wood stove to have an independent source of fresh air, or distribute the heat via existing duct work as mentioned by J King.

 

[NUTTSGT]

Part of the reason your basement is getting so hot is because of the radiant heat from the stove. Radiant heat would be "in direct line" with the stove.

Have you tried something so simple as putting a 20" box fan near the basement stairs to force the warmed basement air upstairs ? Run the fan on low to move the air slowly. . . per my HVAC/plumbing neighbor guy, his theory is that if you try to move the air too fast, it cools down faster.

 

[UpstateNY]

Guys,

Thank you all for your replies and good ideas and concerns.

Gunga,

Yea, mine has the hookups for water circulation, but I don't want to use the radiator method as a first attempt to improving efficiency.

Tractor,

I'm going to wire in a temp sensor so when the wood stove gets cooler it'll automatically shut off the blower fans so no cold air will get circulated.

Boiler,

I have CO detectors in the living space, but I'll keep an eye on the negative pressure sucking gases into the house.

Nutts,

Yes, I kept the basement door open and used a 20" box fan running, it certainly helped get the heat into the living space. This year I'm looking to improve on that by routing the air into the furnace and letting the furnace blower push the wood stove heat around the house.

Gunga,

What is the purpose of that box on top of the burner ? As you stated, mine doesn't have that, but otherwise it's the same as yours.

Joe

 

[Jackfre]

Prior to doing this I would have a radon test done on your basement. The hood over the woodstock works well, but I think you need much larger than 6" to get the best out of this. My father and I did this at his place years ago but we ran the hood up to a 24x24" floor grill terminating in the hall way. No fans. If you put a new register into your furnaces return I would make it so it can be securely closed.

 

[homebuilt burner]

I think if you take some time and make a good tinwork box around the firebox the result should be good. I do not think 1" is enough airgap, more like 3 or 4. Also, if you can affix some metal fins to the firebox the heat output will be much higher.

I built a corn burning furnace a number of years ago, adding fins to the firebox made a huge difference in the heat output. I would make the plenium higher on the top and allow the heat to rise into it. Also, this would be a good spot for a fanstat to control the blower fan.

If you need anymore ideas fell free to pm me but I am not able to be on here alot due to a traveling work schedule now.

 

[NUTTSGT]

Nutts,

Yes, I kept the basement door open and used a 20" box fan running, it certainly helped get the heat into the living space. This year I'm looking to improve on that by routing the air into the furnace and letting the furnace blower push the wood stove heat around the house.


Joe

Well glad to see that you tried a simple fix first.

My old wood stove was a monster and produced great heat on one sid eof the garage, the other side not so much. I took it out and replaced it with a DAKA stove from Menard's. It's basically a stove within a box like you want to create. It uses a snap disc to turn the blower on/off. It's designed to be tied into home furnace/ductwork but I ran one duct up and over through the attic. The second duct has a 90° to direct heat into the garage area.

Here's a link to what parts my stove uses to turn the blower on/off. It might help you locate what you need.

http://store.dakacorp.com/category_s/39.htm

 

[oilslick]

Is that a gasification stove,looks awesome!

 

[UpstateNY]

Jacfre,

Yes, I forgot to mention that I am installing a damper to close the wood stove vent when it's not in use.

Homebuilt, thanks very much for those design ideas, they sound great and I'll adopt them into my solution. I have a fanstart already in my design.

Nutts,

I already have the snapdisc in my design, Amazon sells the same one for $12.00. Thanks for the link, it's a good reference for parts.

Oil,

I'm not sure if it's a gasification stove ?! It came with the house, I'm just trying to get the most out of it.

Joe

 

[ryan77]

years ago in another house I owned I ducted wood stove air in my return air vents, as I felt warm air enter the upstairs vents I felt genious, however a year later when my ductwork was full of ash and dust I felt like an idiot. I would leave it as it sits and let it radiate heat, that is the best method, I had to extensively clean my furnace and ducts of that mess, run an independent duct if you must!

 

[UpstateNY]

years ago in another house I owned I ducted wood stove air in my return air vents, as I felt warm air enter the upstairs vents I felt genius, however a year later when my ductwork was full of ash and dust I felt like an idiot. I would leave it as it sits and let it radiate heat, that is the best method, I had to extensively clean my furnace and ducts of that mess, run an independent duct if you must!

Ryan,

I assume the wood stove was in good shape and didn't have any obvious leaks. Do you think the ash entered the ducts when you opened the stove door to add wood, or was it sucking it through the closed door ?

 

[homebuilt burner]

When I hooked my corn furnace up to my main house duct work, I included a filter mount. I pulled the cold air from the return side of the duct work and put the hot air back in above the natural gas furnace. It did not take long for me to realize I needed a baffle between the natural gas furnace and the hot air entering the duct work. Otherwise the air will just circulate through the furnace and not the house. It took a few tries to get the result I was looking for, so start in October before it is cold and you really need it to work.

Good luck. It sounds like you are thinking in the right direction.

 

[UpstateNY]

Homebuilt,

I was going to just cut a hole in the return duct next to the wood stove, run a duct to the outside of the wood stove to pull air from around it, install a thermostatically-controlled in-line fan in the new duct, and a damper to shut it off when the wood stove is not in use. The furnace filter in the return air duct is 6 feet downstream so it should catch any ash that enters the return duct. I'll have to check the filter more often, of course, for ash.

 

[ryan77]

clean stove, nice set up, or so it seemed, the pipes stayed hot so I never considered a filter close to the stove(fire), I think it was a combo of the door open/closed to add wood and remove ash, and the fact it always is drawing air up around the hot box and there are particles that accumulate and float in the draft, my A-coil was nasty and had ash mud in it as the coils condensated the next summer with a/c on thats when I noticed it, and like I said the ducts were filthy, I did always keep a good quality filter in my furnace and used the fan mode to pull the air thru the house, like i said I thought an awsome set up but that ash has a way of going everywhere. Now if you run deticated ductworks and let the hot air rise naturally to bring the warm upstairs that would be ok, I did that and it was better, it kept the ash out of my furnace, but even with that set up there was ash dust in the deticated duct and my wife noticed more ash dust in the house(settled on furnature), in my new house I have it in the basement(same stove) and just let it radiate, it is alot more clean that way(keeps the ash dust in that corner of the basement.

 

[UpstateNY]

Ryan,

Thanks for sharing your experience. I hadn't thought of the consequences of the A-coil getting ash in it.

A final question: as mentioned above, I have the furnace filter about 6 feet downstream from where I'd be sucking the air in over the stove, and the filter is "before" the fan/heat exchanger/ a/c coil. From your experience, do you still feel that the ash will somehow find a way past the furnace filter and get into the "system" ? I assume that is what happened to you; the filter did not remove the ash. TIA

 

[ryan77]

yea it got past my filter, if you decide to give it a try anyway, clean a section of duct, and after a week check it to see how much ash has acumulated, keep an eye on it.

 

[bobbyjean]

if the water hookups are there......get the hydronic coil in your furnace and its free clean heat... otherwise i would just cut some floor grills in living spaces above basement....you could even get fancy and filter those if you want
yep-the hydronic option will cost more up front but its also clean and fairly maitenence free....it will require a relief valve /dump zone...im sure there are guys on here who can get you good info on that...good luck with it

 

[UpstateNY]

Bobby,

I did hydronic / radiant in my shop floor so I'm pretty well versed with that stuff. I was just looking for something cheap and easy to **** the heat out of the basement but Ryan's experience has me concerned. I was thinking of building a "filter box" utilizing a furnace filter to filter the heated air before it goes into my return duct, but Ryan is suggesting that a regular furnace filter still allows ash particles to pass through.

Man, I don't know what to do. I can't easily get at my A/C coil to clean it so I don't want to gum it up with ash (per Ryan's experience). The safest bet is to just let the stove heat the basement and let the heat rise into the house on its own, and maybe a supplemental 20" box fan on the cellar stairs to push heat up into the living space.

 

[bobbyjean]

the idea of floor registers is a no go? heat rises.... as far as the concern with a-coil...can you switch to pleated type filter the standard pleat will catch about 35% vs. 10% of standard fiberglass filter...of course higher efficiency filters are available.
i use a vornado fan to push the heat from my woodstove down the hall into bedrooms(ranch home) -works pretty good
how about a taller plenum above stove..wouldnt that give solids a better chance of settling?

 

[UpstateNY]

Bobby,

Yea, I don't want to cut holes into the floor; I don't want any permanent hacks on the house. The next owner might not use the stove in the basement.

I have a pleated filter in the furnace now, maybe I'll build a "filter box" using a pleated filter (or something more efficient as you suggest). That'll give me 2 filters in "series" to catch particles. That, and I'll monitor the output of the filter box for the accretion of ash on the vent pipe that'll go to the return air duct. If I see ash building up, I'll stop pulling air from over the stove. Also, I'll research better filters. Thanks much for your ideas.

 

[Bretny]

Hello upstateNY from the poughkeepsie area. I have been useing a wood stove for 25yrs and your 2 story setup is what my father used minus the duct work.

A few things to think about. When you move hot air it cools down. Move the cold air to the hot air. This could be as simple as a duct fan blowing towards your current furnace with an opening pointed at the stove.

One thing my father did was make a large 7ftx8ft heat shield to keep the hot air away from the cold cement wall. Doing this for the floor would help also.

 

[UpstateNY]

Bret,

Thanks for your ideas. The basement is insulated, so the heat loss through the walls will be reduced. I'm just trying to get all of the basement pent-up heat into the 2 stories above. Something more "active" rather than the current passive radiating of the heat upwards through the basement ceiling.

I built a " filter box" today with a thermostatically controlled 20 inch pusher fan. The fan will draw heat over/through the stove and route it into the return air duct. The furnace fan will assist the pusher fan by sucking the heat through the filter box (via the return air duct).

My biggest concern is the ash, so I'll be inspecting the system for any evidence there is ash being drawn into the furnace.

 

[6768rogues]

I have a wood burning furnace with blowers on it in my cellar. I put a duct to my sun porch and another to the main house, with return ducts and their own respective registers. It heats the whole house. I didn't want to screw up my expensive gas furnace by forcing air through it from the wood furnace and I didn't want the air from the gas furnace circulating through the wood furnace when no fire is burning. Also, inline duct fans are often noisy. It sounds as though you are planning to put the fan in the hot air from the furnace. My wood stove duct has discharge air temps as high as 159 degrees; can your fan be in that airstream? Your furnace is closer than my discharge temperature monitor, so your furnace would be subjected to some pretty hot air.

 

[Streetbu]

My previous house had a wood stove in the basement. It would heatthe basement great but i also had a very hard time getting that hest upstairs. A box fan pointed at the side of the stove and in turn the stairs, helped, but only a little. After much thought, I measured where the stove was located in the basement, then transfered those measurements to the first floor. I realized it was not under the bathroom like I had thought, but rather directly under a hallway. I cut a simple 6x12 hole in the hallway floor right against the wall and installed a heating grate in the hole. The next time I started the stove the whole house was warm. All from a simple well placed hole....

 

[UpstateNY]

Rogues,

Does your stove have the fans integral with it's design or did you add external fans ? Good idea about measuring the discharge temps.


Street,

My stove was installed at one end of the house. Regrettably, in my case the register would have to be installed in the den. I do wish the furnace was more centrally located.

 

[6768rogues]

My stove was intended to be a furnace and has an air jacket, two squirrel cage blowers and a filter. It is a green one from Tractor Supply. I have a supply and return to the sun porch and the other duct just heats the cellar, so the floors are warm and the house stay warm.
Interestingly, we built our sun porch about 6 years ago and the NY code allows for 3 season rooms if they have an exterior wall between the house and room and if the room is not heated or cooled by the main heating and cooling system of the house. For that, you get a reduction in energy code requirements for insulation. I ran a wood furnace duct to the sun porch because the code allows it to have supplemental heat. It is well insulated and stays the temperature of the house anyway, but it is hard to fully meet the energy code when the walls are almost all glass.
Noticed you are from Churchville. I am near Brockport, so we are practically neighbors.

 

[UpstateNY]

Rogues,

Thanks for the info. As you can see from my orig post, I'm dealing with a non jacketed stove that came with the house and I'm trying to get more heat injected into the main living area. I do know I could run a separate ducts for just the basement stove, I'll have to think more about doing that.