Is this a crack pot idea?

[doug_under]

I'm installing a Supreme Fusion 24 inserting into my 1947 Kit home.

My home has a metal fireplace, and an ash clean out leading to the basement


The new firebox is designed with a recirculating chamber surrounding it, from which it's twin blowers draw.
It's about the same size as the fireplace



So I'm thinking skip the sheetmetal.

Put a 800cfm fan in the basement, pulling heat through the ash drop.
Assuming the proof of concept works cut a door higher up, line and plumb into my hot air furnace.
Amazon product ASIN B06WGPJ2MQ
Could then use the 3 fans and the furnace fan to control where the heat goes.
I could also keep the sheetmetal but cut around the opening, as it seems to be an effective blocking plate.


I'm I crazy?

 

[webby3650]

Yes, you are crazy.
Use this insert as it’s designed. Altering it is not acceptable for insurance and safety reasons, and hooking it into your hvac system is a disaster waiting to happen. Most certainly these added blowers will reverse the draft and fill your home with smoke. You have natural draft trying to compete with all these mechanical fans. Mechanical fans will win every time if not balanced properly.

 

[bholler]

I second what he said

 

[billb3]

I'm I crazy?

Quite possibly.
Most people that try to move wood stove heat down accomplish very little but make a lot of noise accomplishing it.

 

[doug_under]

The heat circulation is surrounding the firebox, not in it.
I wouldn't be modifying the combustion process at all.

I'll post pictures with the stove in place and the ash trapdoor removed.
That will make more sense.

What I'm getting at is akin to how a down draft cook stove works.

 

[maple1]

Aside from whatever else might be wrong with this idea, I am pretty sure it would end up plain not worth the effort if it was tried. You would get very little heat out of the ends of your ductwork from it. IMO.

 

[webby3650]

I know what you are talking about, no need to see the stove in place. My biggest concern is all the mechanical fans especially the furnace blower causing a draft reversal.

 

[barnaclebob]

The heat circulation is surrounding the firebox, not in it.
I wouldn't be modifying the combustion process at all.

I'll post pictures with the stove in place and the ash trapdoor removed.
That will make more sense.

What I'm getting at is akin to how a down draft cook stove works.

I think the risk is generating negative pressure near the fireplace by trying to suck air down to the basement or elsewhere. When the fire dies down, the chimney draft weakens, and your furnace kicks on it will suck air from around the firebox, but where does that "return" firebox air come from?

Additionally while inserts and stoves get really hot, they aren't the best heat exchangers. If you tried to blow a high volume of air past one it might only make the air a few degrees warmer.

 

[bholler]

The heat circulation is surrounding the firebox, not in it.
I wouldn't be modifying the combustion process at all.

I'll post pictures with the stove in place and the ash trapdoor removed.
That will make more sense.

What I'm getting at is akin to how a down draft cook stove works.

Yes we know that the heat circulation air and combustion air are separate. But by pulling circulation air out of the space with mechanical fans going to a different area you will be crating a negative pressure area near the stove. With natural draft appliances that is a very bad idea

 

[sadpanda]

Pulling air from one room/floor to another with dedicated ducts/ fans works pretty well (especially if you don't fight physics and help the heat rise) Trying to tie it into your HVAC doesn't work (generally not generating enough heat to heat duct work AND air) AND is a super big no no. In fact, ducts like I mentioned have specific rules in NFPA. Look em up before planning /cutting)

Properly commissioned HVAC is a balanced flow system... You aren't going to depressurize anything as long as you have proper returns etc. Fans that exhaust to a different air space (ie bath/range hood) can depressurize the home but not likely with 70s construction. If you tried to close your other returns and only return from around this box, yes probably enough volume to cause some issues but a simple manometer on the chimney to verify natural draft before and during fan operation would be simple insurance.


Speaking of 70s construction, unfinished basement like that are massive energy holes. You could have a dedicated pellet stove down there and it would probably still feel chilly... Without air sealing/insulation you are just dumping the heat into the ground.

So IMHO, hair brained, no. Likely to defy the laws of physics and suck coals out of the fire box, no. Likely to have the desired result, no.

 

[jetsam]

If you have a tight house, this is probably a severe CO hazard. The fan pulls 800cfm downstairs, you get draft reversal on your flue on a warm night when the fire is down to coals, and you're suddenly pumping combustion exhaust into your furnace, probably while you are in bed (draft on the flue gets weaker as the fire burns down).

Whether or not it works for heat distribution, you shouldn't mess with it. Same reason it's not okay to have a vent hood above a basement stove.

 

[sadpanda]

Where exactly is the 800cfm suppose to go? especially on a tight house? 800 CFM is basically a box fan... how is 800cfm going from one space to the other inside the same envelope and with 'normal' obstructions (hallways/open doors) going to depressurize anything?

Like I said before, the biggest issue is its not going to work as intended. I've attached a graph from one of my burns... I have a probe parked maybe 1/2" above the top plate, just behind the CAT. As you can see, the forced air coming from the air shroud really doesn't change during the burn and isn't really all that hot. I may try moving the probe forward this year to try and capture more of what the CAT contributes but to echo what as been said earlier, the stoves are radiators NOT forced air units. I'm thinking most factory fans are 100-200CFM max.

 

[maple1]

Where exactly is the 800cfm suppose to go? especially on a tight house? 800 CFM is basically a box fan... how is 800cfm going from one space to the other inside the same envelope and with 'normal' obstructions (hallways/open doors) going to depressurize anything?

Like I said before, the biggest issue is its not going to work as intended. I've attached a graph from one of my burns... I have a probe parked maybe 1/2" above the top plate, just behind the CAT. As you can see, the forced air coming from the air shroud really doesn't change during the burn and isn't really all that hot. I may try moving the probe forward this year to try and capture more of what the CAT contributes but to echo what as been said earlier, the stoves are radiators NOT forced air units. I'm thinking most factory fans are 100-200CFM max.

View attachment 249772

It will cause a pressure drop in the area of the fan inlet, and a pressure increase in the area of the fan outlet. That's what moves the air. That pressure drop might be just as likely to cause combustion gasses to leave the firebox and move to the fan inlet, as room air to move from another area of the house to the fan inlet. Particularly at or towards the end of a burn when chimney draft will have decreased but there are still gasses being emitted (carbon monoxide).

 

[sadpanda]

the area of the fan inlet

yep. combustion inlet is probably on the front of the stove and this proposed inlet is at the back/bottom. As far away or further then the fan that is installed on the insert... oh wait! there is a fan on insert? wont that depressurize the area and suck CO2 into the house?

OP: NFPA has guidelines for ducts around solid fuel heaters. Directly over the heater is prohibited so I'm sure directly under the device is prohibited as well. NFPA reasoning is not depressurization it is quite literally for fire spread.

 

[jetsam]

Where exactly is the 800cfm suppose to go? especially on a tight house? 800 CFM is basically a box fan... how is 800cfm going from one space to the other inside the same envelope and with 'normal' obstructions (hallways/open doors) going to depressurize anything?

You can get draft reversal with no fan at all. The fan adding a low pressure area near the stove's air intake won't help if this occurs, and then whatever comes out of the stove gets sucked in by the fan.

It's not a high-probability outcome, but it is something that could kill you without warning in the middle of the night, just because the weather is warmer or the wind is different than it was the night before.

If you think it's a one in a million chance, search this forum for people asking why their CO alarms are going off. It's not that rare.

Honestly, it would probably be ok, but the consequences are potentially really severe on that one night when it's suddenly not ok. Why play with that?

 

[PaulBunyun]

Would you be circulating the warm air through your furnace cold air return then back through the system. If so then bad idea as HVAC systems are delicately balanced and shouldn't be altered outside specs. As for your insert itself many other people have touched on the issues it would cause. My vote: dont do it and just enjoy your insert as is. When I had my insert installed I made sure the ash drop was sealed for two reasons. One being that I didn't want a pressure/air issue and two I didn't want to lose heat to a space I dont need heated.

 

[MinM]

If you have forced hot air, why not just run the insert as designed and use your furnace fan to recirculate the air throughout the house?

 

[begreen]

If you have forced hot air, why not just run the insert as designed and use your furnace fan to recirculate the air throughout the house?

If the entire duct system is insulated, sealed and runs through the heated envelope of the house, this might be effective. However, it can be a hit or miss proposal depending on how well insulated the ductwork is. The furnace is designed to circulate 130º+ air and often the system has a fair amount of loss in the supply and return duct runs. Often this loss can be 20º. Unless it is an insulated system, many are not designed to circulate the ambient 85º air.

 

[mcdougy]

IME, running the furnace fan distributes the the air pretty effectively. I have a 3 degree celcius max difference in all rooms, basement included. Stove room being the warmest obviously, but the dog doesn't mind.