Shop stove build and buffeting/back puff from the air intakes- ideas?

[IDfamforest]

Greetings All,
I recently built a wood stove out of a modified heating oil tank (1st pic) based on a design I saw on youtube (2nd picture). We had a large garage built 2 summers ago and originally tried to heat it w a fisher papa bear (3rd pic). the fisher install is 6 inch pipe straight up to the roof from a rear exit stove. insulation for the garage/shop is the standard pull building insulation that comes with a kit ( reflective on one side approximately 3 inches of material sandwiched between the exterior tin and the girds. Shop is 2100 ft.² floor space with 14 foot walls in an open truss ceiling. There is a ceiling fan installed. as one might guess, the papa bear does not heat the shop very well. During the winter with temperatures in the 20s outside, temperatures in the shop are 35 and after running the stove on to full loads temperatures are only up into the 40s. insulation in the roof will eventually be installed but building the stove was a much less expensive solution to try and increase the heat in the shop this winter.
Watching YouTube, I saw the modified tank and a larger shop and the gentleman (tom bicandi

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) seemed to be very happy with it. he used an 8 inch exhaust pipe.
Seeing as I had most of the material close at hand and I wanted a welding project I decided to build a similar stove. I am using the original 6 inch pipe but due to the top exit on the stove, in order to maintain appropriate distances from the heat source 1 needed to place 2-45° bends in the exhaust pipe. Setback is about 22 inches from a tin heat shield with a 1 inch air gap using pipe as a spacer.
If he heats pretty well and yesterday I was able to bring the shop temperature up to 70 degrees. I am still considering whether am going to modify it by putting more heat exchange tubes in. I will be using a squirrel cage blower and fashioning a shroud for the blower at a later date. Currently I have a 20 inch industrial fan with roof tin as a make shift shroud around the posterior pipes as a temp fan/blower.

This is the problem... I get pretty serious by back puffs/buffetting on start up as it is getting to temperature. Makes a little smoky in the shop. any ideas on how to make that go away? I am using 2-3/8 inch pipe from a exchanger tubes and my air intake. Eventually I will be adding more exchanger tubes probably 6-8 more and then I will clean the surface and paint it. Although not seen in the picture, a fire extinguisher is handy.

I appreciate your input.
RP

 

[EbS-P]

My definition of backpuff is spontaneous combustion/detonation of exhaust gasses. Is a draft reversal or a backpuff?

 

[IDfamforest]

It is back puffing. There is an audible buffeting sound (puh-puh-puh-puh-puh) that accompanies flames rhythmically popping out of the intake pipes and puffing smoke into the shop. This is w the flue damper wide open. I have to close the air intake tubes to make it stop.

 

[EbS-P]

To much smoke not combusting then getting somewhere hot enough to combust. In the video still that you posts you can see the exchange tube is glowing. So he’s running HOT.

Personally I’m not a fan of this design. Yes it works but it’s not efficient and possibly a creosote factory unless the tubes are glowing. If it were me. I’d have a baffle and a stainless steel secondary air system. Burn that smoke in the firebox.

My quick remedy. Try lighting top down and reload like you are lighting a top down. Keep active flames near the exhaust path.

 

[IDfamforest]

I considered adding a baffle and 2ndary burn tubes when I had the back wall off after cutting 2 feet off the tank but I didn't have all the necessary supplies. If I build another stove it will have secondary burn and made out of a 30 inch diameter pipe I have. I've considered modifying the fisher w/ a baffle, secondary heat. and heat exchangers- I could get at least 8 - 2 inch pipes in the upper chamber but I strill think it would still be small for the size shop and possibly limit the firebox capacity. If it didn't work for my purposes I'd have ruined the market value (for what that is worth about $400-500 in my area).

For a large firebox capacity, would a wider (8 in) exhaust work better? As I mentioned I used the existing 6 inch system.

 

[stoveliker]

I wonder if you are getting enough air in the box.
Back puffing happens after closing down a fire too much too suddenly. I.e. more gases produced than the draft can suck out.

I'd add an air inlet, possibly right above the door (under the tubes) to burn things in the top and not in the back so you're not mixing colder air into the chimney.
Or a long tube from the back that brings air to the front top (so the air can heat a little before seeing gases).

 

[EbS-P]

Or a long tube from the back that brings air to the front top (so the air can heat a little before seeing gases).

This make it T and add a piece of vermiculite above it. And it got secondary combustion. But I would bring it in low. 90 up, 90, horizontal then T. But keep it near the back 1/3. Trying to keep flames off the exchange tubes.

 

[bholler]

It isn't able to evacuate the smoke fast enough because it's only a 6" vent

 

[IDfamforest]

Thanks for the replies.

I was wondering about the 6 inch exhaust... I'm not quite ready to cut a bigger hole in the roof but I'm likely going to. If there is too much smoke not being able to exit due to the 6 inch pipe, do you think that adding an 8 inch exhaust up a several feet and then reducing to 6 inch would help at all?

In the interim, I found that not having such a raging fire on start up and bringing it up to temp a little slower with smaller fire helps quite a bit.

Cheers.

 

[gthomas785]

At first glance I'd agree with the others that it's probably undervented. Going to an 8" flue would make a big difference.
Also if anything I would cut down the intake area a little bit to keep the firebox pressure negative. And move the intake further from the coals, use some portion for secondary combustion, etc.

 

[bholler]

Thanks for the replies.

I was wondering about the 6 inch exhaust... I'm not quite ready to cut a bigger hole in the roof but I'm likely going to. If there is too much smoke not being able to exit due to the 6 inch pipe, do you think that adding an 8 inch exhaust up a several feet and then reducing to 6 inch would help at all?

In the interim, I found that not having such a raging fire on start up and bringing it up to temp a little slower with smaller fire helps quite a bit.

Cheers.

You do know that solid fuel appliances are not allowed by code to be installed in any garage in the usa right?

 

[IDfamforest]

Thanks for the info.

Before we installed ANY wood stove stove, we confirmed w the county and insurance that it is legal and insured even w/ vehicles, and appropriate fuel storage. Recently I confirmed that a home built stove is covered under our insurance also- no exclusions.

Doing a search I found that this can be a contested issue, much like pot is illegal to the feds but not to WA, CA, OR, and many other states. I suppose this is where state laws win out over federal guidelines.

I appreciate the input and advice.

 

[bholler]

Thanks for the info.

Before we installed ANY wood stove stove, we confirmed w the county and insurance that it is legal and insured even w/ vehicles, and appropriate fuel storage. Recently I confirmed that a home built stove is covered under our insurance also- no exclusions.

Doing a search I found that this can be a contested issue, much like pot is illegal to the feds but not to WA, CA, OR, and many other states. I suppose this is where state laws win out over federal guidelines.

I appreciate the input and advice.

What state are you in?

Also make sure you have it in writing from the underwriter not just the word of your agent about it being covered. I have been involved in enough insurance cases after the fact to be able to tell you that what your agent says even in writing doesn't matter in the least.

 

[IDfamforest]

ID. The county requires 18" off the ground for the firebox. I need to check my measurements. Thanks again.

 

[bholler]

ID. The county requires 18" off the ground for the firebox. I need to check my measurements. Thanks again.

Ok so Idaho follows nfpa 211. Which clearly states this. Your county cannot override state codes.

 

[bholler]

I am just trying to make sure you have accurate information regarding this issue. If you choose to go with it anyway that's entirely up to you. Many people including myself decide the risk is worth it. But it absolutely is a risk.

It does look like your heat sheild does need to be wider behind the stove

 

[IDfamforest]

The county does permit stoves in garages as mentioned. I'm not sure about the legalities, but if the county signs off on a stove permit then it's legal. I did check with them again, today and learned that the UL listed Fisher PBear is approved but the home built superheater is not. Insurance covers it though. Weird. In regards to risk, it is one currently taken.

I will be upgrading the roof insulation this summer. I will likely look for a summer sale priced stove that is UL and EPA certified that works w 6 inch flues. The Ashey 3200 sq ft model or the ENglander NC32 might be the ticket for affordable high output heat w/o cutting a bigger hole in the roof although a BK King would be great too( a BK recently sold for $1000 in FM marketplace around here).
Shop heating season is almost over.
I appreciate the info.

 

[kborndale]

Just because the county signs off on it doesn't mean the insurance company will pay you if things go bad. And the county does not supersede the state.

 

[bholler]

The county does permit stoves in garages as mentioned. I'm not sure about the legalities, but if the county signs off on a stove permit then it's legal. I did check with them again, today and learned that the UL listed Fisher PBear is approved but the home built superheater is not. Insurance covers it though. Weird. In regards to risk, it is one currently taken.

I will be upgrading the roof insulation this summer. I will likely look for a summer sale priced stove that is UL and EPA certified that works w 6 inch flues. The Ashey 3200 sq ft model or the ENglander NC32 might be the ticket for affordable high output heat w/o cutting a bigger hole in the roof although a BK King would be great too( a BK recently sold for $1000 in FM marketplace around here).
Shop heating season is almost over.
I appreciate the info.

Read the fine print on that permit. They are not held liable for any mistakes or omissions in their permitting or inspections.


The ul listing thing is a gray area. Nfpa 211 allows for unlisted stoves. But the international mechanical code does not. But insurance companies can require whatever they want. Or overlook any code violation they want. But it all has to be in the policy. If it's not and something happens the adjuster isn't going to care what your agent said

 

[IDfamforest]

update...

I spoke w a friend, former county building inspector and asked about county v state rules. He advised that the county has jurisdiction over this issue. Their local rule applies. Learned that the installer did not install it permitted. County will do an inspection. They will not approve a non- UL stove. I'll review my policy w the agent and have him show me the fine print. If he can't well... any risk falls on the user. I had been under the mistaken impression that my Fisher was UL listed. Not sure how I missed it but it's not. I bought a 30 NC off FB for a reasonable price ($350) and installed it last night according to county reg and manufacturer clearances. Lit a fire last night to test out the 30NC... had one at our prior home... I sure do like the secondary burn. This discussion has had me think about several items. I am now more informed and appreciate it.

 

[bholler]

update...

I spoke w a friend, former county building inspector and asked about county v state rules. He advised that the county has jurisdiction over this issue. Their local rule applies. Learned that the installer did not install it permitted. County will do an inspection. They will not approve a non- UL stove. I'll review my policy w the agent and have him show me the fine print. If he can't well... any risk falls on the user. I had been under the mistaken impression that my Fisher was UL listed. Not sure how I missed it but it's not. I bought a 30 NC off FB for a reasonable price ($350) and installed it last night according to county reg and manufacturer clearances. Lit a fire last night to test out the 30NC... had one at our prior home... I sure do like the secondary burn. This discussion has had me think about several items. I am now more informed and appreciate it.

Good that is always my only goal in bringing this up. As I said I chose to install a woodstove in one of my garages knowing the risks. So obviously I have no issue with people doing that. I just want them to understand those risks