New Woodstover Questions - Green Mountain 40

[Mucully]

Hey everyone, I’m a longtime reader and this is my first post. I want to start off by thanking everyone who regularly contributes to the forums as I’ve used what I’ve learned on here to pick my wood stove (a Hearthstone Green Mountain 40). So far I love it and have had a few successful fires! I have a few questions I’m hoping can be answered so I get the most out of my new stove.

1. Are fire starters made with sawdust and paraffin wax acceptable or is the paraffin wax going to gunk things up and cause unsafe buildups?

2. I’ve gotten my stove well into the catalytic range as indicated by the built in thermometer but didn’t see any visible difference in the fire. Should I be seeing anything happen or is the cat just reburning the background?

3. I’ve found a guy in my area with a steady supply of kiln dried red oak scraps for a good price. I’ve heard that kiln dried is too low of a moisture content and actually burns worse than logs with a 10-20% content. Is this true or can I burn these kiln dried pieces?

Thank you again to everyone who contributes! I’ve attached some pictures of my new stove and (unfinished) hearth that I built.

 

[begreen]

The small firestarters are ok. Burning a wax-impregnated sawdust log like DuraFlame is not ok. The oak scraps should be ok, especially for smaller fires. For larger fires try mixing them in with full-sized splits.
This is a hybrid stove so the cat is doing cleanup duty on the exhaust gases.

 

[mdocod]

Hey everyone, I’m a longtime reader and this is my first post. I want to start off by thanking everyone who regularly contributes to the forums as I’ve used what I’ve learned on here to pick my wood stove (a Hearthstone Green Mountain 40). So far I love it and have had a few successful fires! I have a few questions I’m hoping can be answered so I get the most out of my new stove.

Congratulations on the new stove. I love the looks of the GM series!

1. Are fire starters made with sawdust and paraffin wax acceptable or is the paraffin wax going to gunk things up and cause unsafe buildups?

I routinely burn wood that is rich with resin/pitch , which is similar to wax, which spews sooty black smoke out to be burned up in the heat of the secondaries.

I am confident that there is no wax soaked fire starter that is "worse" for the stove system than the garbage wood I burn through the stove on a regular basis. You should be fine!

2. I’ve gotten my stove well into the catalytic range as indicated by the built in thermometer but didn’t see any visible difference in the fire. Should I be seeing anything happen or is the cat just reburning the background?

When clean, the cats and the redirected path for the exhaust on these stoves are is much less restrictive than the maximum airflow setting on the inlet side, so you won't see much if any change in the fire in the box when engaging the cats. It probably only effects the rate of airflow through the box by 5-10% at maximum airflow settings. At low-burn-rate settings it accounts for even less restriction.

By redirecting the flow through the cats, you're essentially "Scrubbing" the exhaust to pull down emissions and get a little bit more heat out of the system during active flaming fire. You won't notice much going on with the cats while there's active fire in the firebox, as during this time, something like 90-99% of the wood gas is being burned off in the firebox through primary and secondary combustion. If you burn smaller loads of very dry wood at high/hot burn rates, you may never notice much impact from the cats, as nearly all the wood gas will be expelled from the fuel load at a rate that supports active flaming.

Where the cats really make a difference for these stoves, is when they are operated at low burn rates. After bringing the stove, cats, and chimney system up to operating temps with a hot fast startup burn, the stove can be choked down to very low steady burn rates. These low burn rates will eventually transition from a flaming fire to a smoldering fire in the firebox before all of the wood gas has been expelled from the wood. When this happens in a hybrid stove, the combustion of the wood gases transitions from flames in the firebox to the catalytic combustors. The wood can smolder away slowly while the cats burn off the gases in a smaller "fire" downstream of the firebox. As the cats do this, they get very hot, radiating heat into the upper/rear part of the stove, and in this design, the position of the cats is intended to promote the maintenance of sufficiently high EGT's during wood gas combustion for long term chimney system health and safety.

Many folks on this forum will argue that the cats in this design provide no benefit to the consumer. I don't believe this is true. You get access to lower burn rates that would not be possible within emission standards without the cats, cleaner exhaust, cleaner chimney, and about 10-15% more heat in the home for a given fuel load compared to their previous stove designs.

3. I’ve found a guy in my area with a steady supply of kiln dried red oak scraps for a good price. I’ve heard that kiln dried is too low of a moisture content and actually burns worse than logs with a 10-20% content. Is this true or can I burn these kiln dried pieces?

I would get a moisture meter, split a piece, and take a measurement from the inside of the wood and see what it actually is. There generally nothing wrong with being dryer than 10%, it just promotes a faster, hotter burn, so that needs to be accounted for in how the fuel is loaded/spaced and what air settings are used to control the burn. Sometimes kiln dried means "dry on the outside, still wet on the inside."

Are the scraps dimensional or rough/random shapes? What sort of size range?

The difference in behavior between oak at say, 7% and 20%, may be meaningful, but it's still not as much of a range as the stove is intended to deal with when we consider all possible wood species that could be burned in the stove. I'm burning soft ponderosa at 9% moisture, and it works fine.

Thank you again to everyone who contributes! I’ve attached some pictures of my new stove and (unfinished) hearth that I built.

View attachment 307718 View attachment 307719

Beautiful!

 

[Mucully]

The small firestarters are ok. Burning a wax-impregnated sawdust log like DuraFlame is not ok. The oak scraps should be ok, especially for smaller fires. For larger fires try mixing them in with full-sized splits.
This is a hybrid stove so the cat is doing cleanup duty on the exhaust gases.

Thank you so much for your reply. Yes I definitely know to stay away from DuraFlame logs. I'm just using small breakable squares of a fire starter so good to know I can keep using those.

Good advice, I have about a cord of mostly seasoned cord wood (22-23% on a fresh split), so mixing the kiln dried in with that would probably be perfect.

Good to know on the cat.

Thank you again!

 

[Mucully]

Congratulations on the new stove. I love the looks of the GM series!

Thank you!

I routinely burn wood that is rich with resin/pitch , which is similar to wax, which spews sooty black smoke out to be burned up in the heat of the secondaries.

I am confident that there is no wax soaked fire starter that is "worse" for the stove system than the garbage wood I burn through the stove on a regular basis. You should be fine!

Great to know, thank you!

When clean, the cats and the redirected path for the exhaust on these stoves are is much less restrictive than the maximum airflow setting on the inlet side, so you won't see much if any change in the fire in the box when engaging the cats. It probably only effects the rate of airflow through the box by 5-10% at maximum airflow settings. At low-burn-rate settings it accounts for even less restriction.

By redirecting the flow through the cats, you're essentially "Scrubbing" the exhaust to pull down emissions and get a little bit more heat out of the system during active flaming fire. You won't notice much going on with the cats while there's active fire in the firebox, as during this time, something like 90-99% of the wood gas is being burned off in the firebox through primary and secondary combustion. If you burn smaller loads of very dry wood at high/hot burn rates, you may never notice much impact from the cats, as nearly all the wood gas will be expelled from the fuel load at a rate that supports active flaming.

Where the cats really make a difference for these stoves, is when they are operated at low burn rates. After bringing the stove, cats, and chimney system up to operating temps with a hot fast startup burn, the stove can be choked down to very low steady burn rates. These low burn rates will eventually transition from a flaming fire to a smoldering fire in the firebox before all of the wood gas has been expelled from the wood. When this happens in a hybrid stove, the combustion of the wood gases transitions from flames in the firebox to the catalytic combustors. The wood can smolder away slowly while the cats burn off the gases in a smaller "fire" downstream of the firebox. As the cats do this, they get very hot, radiating heat into the upper/rear part of the stove, and in this design, the position of the cats is intended to promote the maintenance of sufficiently high EGT's during wood gas combustion for long term chimney system health and safety.

Many folks on this forum will argue that the cats in this design provide no benefit to the consumer. I don't believe this is true. You get access to lower burn rates that would not be possible within emission standards without the cats, cleaner exhaust, cleaner chimney, and about 10-15% more heat in the home for a given fuel load compared to their previous stove designs.

This is the BEST explanation of a cat, how it works, and how it affects my fire/ stove that I've ever read. THANK YOU!!

 

[Mucully]

I would get a moisture meter, split a piece, and take a measurement from the inside of the wood and see what it actually is. There generally nothing wrong with being dryer than 10%, it just promotes a faster, hotter burn, so that needs to be accounted for in how the fuel is loaded/spaced and what air settings are used to control the burn. Sometimes kiln dried means "dry on the outside, still wet on the inside."

Are the scraps dimensional or rough/random shapes? What sort of size range?

The difference in behavior between oak at say, 7% and 20%, may be meaningful, but it's still not as much of a range as the stove is intended to deal with when we consider all possible wood species that could be burned in the stove. I'm burning soft ponderosa at 9% moisture, and it works fine.

I've attached a screenshot of the listing, but it looks to be essentially wood working blocks (dimensional) that appear to be very dry. Good to know about the moisture content, thank you. After reading begreen's reply I think I'll probably mix it in with some mostly seasoned (22-23% on a fresh split) cordwood.

 

[outdoorguy864]

I really like the word being used for the cats on these stoves "scrubbing", as that explains it well on this hybrid. I also have a GM40, this is my third year on it. Couple of tips, these stoves shine with the secondary air burn, its pretty impressive how well it works. So your seeing a flame, but the flames are 80% at the top above the wood. Once you figure it out, you can get the secondary to be about 95% of the flame and below the wood is dark/black with no flame. When you figure it out, took me awhile, how to repeatedly have that secondary burn consistently, it is a really efficient fire and then when your down to coals, let it keep burning down, the soapstone and castiron will keep those coals going for a really long time and then reload. I feel like this is how the stove was designed to run, but i could be totally wrong, haha.

I also have found that, for startups and reloads, get the fire going kind of hot, than (once cat lever is engaged for a bit), adjust the primary air control in stages. You will knock the fire down bit by bit (like.....every 10 minutes'ish), but it will kind of rebuild. I typically will do it until i have it closed all the way and then let it cruise until next reload. Usually is 2 to 3 adjustments to get it fully close. All depends on reload temps, etc.

 

[GM80NY]

I really like the word being used for the cats on these stoves "scrubbing", as that explains it well on this hybrid. I also have a GM40, this is my third year on it.

I also feel like I got the hang of it after 2 1/2 seasons.

Congrats on the new stove!

To your second point about the fire not really changing. Yes this is a good thing and a thing to watch for. When you engage the catalyst, and the flame dies off fairly quickly it could be a few things. Catalysts might be clogged with ash and it will happen eventually, wood isnt dry enough, not hot enough in the firebox, oxygen in the room isnt sufficient to keep the flame going or a combo of these.

Keep an eye above the baffle every so often. The gasket for the bypass door can fall down. This is also a common issue.

Enjoy the stove man! I definitely feel like im going way slower through my wood piles this season and I started burning earlier than last season.