Help sizing a Catalytic stove

[tabner]

In the process of removing my oil boiler and installing a mini split, ductless, heat pump/AC system. For the dual purpose of central air, but more importantly switching to primarily wood heat. By removing the boiler, I have an empty chimney for a basement woodstove! Looking for some insight on stove sizing. I understand the catalytic stoves CAN burn low and slow, however reading the manual on the hearthstones, they recommend you not exclusively burn on low, due to creosote build up, inefficiency, etc.
My home is right around 1600 sq ft, maybe a hair less. It is a salt box (think of a small cape without the dormers). Stove will go in the semi finished basement, which is about 500 feet of insulated space, heat will rise up the stairway and through a couple floor registers, to the second floor (or first depending how you look at it) which is about 700 square feet of living room, dining room, guest room, etc. And then I have a sort of half cathedral ceiling design where it's open to a small walkway with two small bedrooms and the bathroom (similar to a cape layout). So about 400 sq feet on that top floor. The house is very efficient I believe, i don't have a formal heat loss measurement, but it is 2" x 6" construction, built in '87, with newer/updated double glass windows. It also has a long roofline on the salt box design that faces due south, with a sky light and sliding glass doors - during the day, even in the winter, we definitely get some passive solar. I'm in Eastern Connecticut.
Looking at the HearthStone Green Mountains, i have a dealer nearby that is very good, and they will give me a 10% cash/carry discount.
Trying to decide between the 40 and the 60. The 40 technically says up to 1400 square feet, and the 60 says 2000. I know most things in life, bigger is better, but again, my house seems to be very efficient, and i don't want to oversize a catalytic stove (never owned one before) and end up running it with the air fully closed down 85% of the time.
I will technically have heat pump wall units as heating backup. I will be burning well-seasoned oak and maple.
Any thoughts/feedback is greatly appreciated.

 

[moresnow]

Any thoughts/feedback is greatly appreciated.

Put the stove on the main floor. Where you live. Really research basement installs thoroughly. More potential challenges and significant heat loss/back draft/smoke roll out issue's etc.
My opinion only.

May want to do some in depth research on the new Green Mountain model stove's as well. Plenty to learn here and on related site's from the handful of user/members.

What make/model mini split system did you purchase? Curious.

 

[tabner]

thanks for the feedback moresnow. Unfortunately stove on the first floor is really not an option. The house is small with small rooms. The available spots i'd have to put it, within reach of the chimney, would completely cut up the floor plan, and the wife won't hear about it.
for what it's worth, the basement is about 75% finished, and the stove would be in a finished, insulated space. So there should be minimal heat sink into the cement walls or floor (carpeted floor). And the room the stove would be in is a den-type area, so while we do spend much more time upstairs, we watch TV and play video games, etc, in the basement where the stove would be. for what it's worth, i do intend to get the blower kit for the green mountain. It will be pointed in the direction of the stairwell, so hopefully moving as much warm air across the den and up the stairs as possible. Also, the basement is a walk out basement on one side, walks out into my garage, where i'd be stacking wood. So it's ideal from a wood storage, less mess in the house, standpoint. Anywhere on the first floor you have to come up a stairway, so all wood would have to come up stairs. And finally, if the woodstove is on the first floor, i assume i'm going to get zero heat down the stairs, which isn't really an option because we do spend some time down there in the den, and doing laundry, etc. I'm not saying you're wrong, just pleading my case
Would you still say it's not worth it? or is it doable?

The mini split would be a mitsubishi, with the hyper heat pump so it heats at lower temps (if i ever needed it to). I'm not positive on the model yet, i have been quoted on two sizes, but it kind of depends on what i decide with the woodstove, as theyre related from a heating standpoint. i was quoted on a 4 head setup (16k$) or a 3 head setup (11k$). (price includes full install and 3 year warranty including labor, 12 year on the parts). The 3 head setup is a 15k BTU head on the first floor, and two 6k BTU heads in each of the upstairs bedrooms. Again, AC and heat. The hope would be we'd have a nice AC system for the summer, and then heat 90% with wood in the winter and just have the heat pump as an option (plus i have to have some type of alternative heat for home owner's insurance, they won't let it be only wood).

 

[tabner]

The chimney is centrally located in the house too, so it goes straight up through the middle of all floors and out the peak. I'm hoping that would make it likely i have a good draft?

 

[moresnow]

Many people heat successfully from the basement. Some with zero issue's. Just a heads up that it's worth researching. Your overall plan sounds solid. If it were my only option I'd sure try it!

The Mitsubishi systems sound nice. Post how that works out when it gets up and running.

 

[begreen]

If the goal is 24/7 heating then for sure get the GM60. 2 cu ft is not a large stove. Its low output is around 12K BTUs or a bit more than 2 electric heaters worth. The other alternative if sold locally would be a BlazeKing Sirocco or Princess. These stoves are pure catalytic and thermostatically regulated. That allows a longer burn at low heat without overwhelming the space.

 

[Highbeam]

The hearthstone catalytic stoves are new and have yet to earn their stripes as a cat stove on par with the established good reputations of blaze king and Woodstock. Just the fact that they don’t want you to run them on low very much tells me that they are not designed to be the same kind of stoves you want when choosing a cat stove. May as well skip the complication and cost of a catalyst and go with a good noncat if you aren’t supposed to run them low and slow.

The GM series sure looks good though and any stove in your daylight/mostly finished basement is where I would put it if you spend much time down there. Hot air rises after all.

You’re removing a boiler to install forced hot air? What the heck will happen with your radiators or other hot water equipment?

 

[tabner]

The hearthstone catalytic stoves are new and have yet to earn their stripes as a cat stove on par with the established good reputations of blaze king and Woodstock. Just the fact that they don’t want you to run them on low very much tells me that they are not designed to be the same kind of stoves you want when choosing a cat stove. May as well skip the complication and cost of a catalyst and go with a good noncat if you aren’t supposed to run them low and slow.

The GM series sure looks good though and any stove in your daylight/mostly finished basement is where I would put it if you spend much time down there. Hot air rises after all.

You’re removing a boiler to install forced hot air? What the heck will happen with your radiators or other hot water equipment?

Thanks Highbeam and Begreen. No forced hot air, ductless mini split is different. The way our house is setup with passive solar, we basically bake in the summer. Regularly the house is over 82 degrees (and humid) inside. I'm sick of lugging multiple window units around in the spring and fall and paying to run the ugly noisy things. Since the house does not have any duct work, the closest we'll ever get to central air is a ductless mini split system. A mini split system with just AC for the whole house is in 8 to 9 k range. might as well spend 11 to 12k, make it an AC and heat pump system, pull out the oil boiler and put in a woodstove so i don't ever actually heat with the electric. I live on 5 acres that is covered in large Oaks that are all dying from the gypsy moth caterpillars the last couple years. and my grandfather lives next-door on 10 acres with the same issue. I have enough wood for free, on site, to heat my house for at least a decade, i can't stand not using it. Also, oil is cheap now, but it might not always be, i'd really sleep better at night knowing i'm setup for wood. I know it doesn't make complete financial sense, but i'd really like to burn wood. I could keep the oil/radiator system and tie in an outdoor wood boiler, but i'm going to spend 15k there anyways, and not have AC. The oil boiler works, but is noisy, the tank takes up space in the finished basement, the radiators make noise all night, etc, it's not exactly a perfect setup. The boiler is 13 years old. I'll probably try to sell it on craigslist. interested?

 

[ABMax24]

Don't be concerned about heating from the basement, many of us do it without any issues. Personally I really like it, in the summer the basement is nice because it's cool, in the winter it's nice because it's warm. I don't think you'll have draft issues unless you already have pre-existing differential pressure issues within the house, ie insufficient outside air supply. The only time I have issues is if I try to light a fire when outside temps are above freezing and the wife starts the dryer at the same time. The dryer pulls the smoke right back down the chimney, but even then the fix is simple, open the window next to the stove until the draft gets better established.

 

[kennyp2339]

Floor vents for passive heating does not work as advertised unless they are built as cold air returns, since cold air is denser and will sink the return is more favorable then thinking of busting a few holes to let heat rise.
For a cold air return you will want a minimum of a floor joist space wide x 20" with a fusible grate, these should be located more or less on the envelops of outside walls in the room, then underneath the area should be boxed out 16" to allow the sinking air not to mix with the basement hot air. once the cold air leaves that space it will naturally get filled in by lighter warmer air.

 

[stoveliker]

@tabner, I have a Mitsubishi split ductless. 18k in the living room, 6k in two bedrooms each, and 6k in the basement. 1700 sqft (w/o counting the finished basement of 650 sqft). And solar panels providing for AC and heating with the split ductless.

Then I have a new (see a 2020-21 BK performance thread) blaze king chinook 30 cat stove in the basement. (After removing an old cat stove that was there.)
I can heat my living space above the basement to 70ish easily from the basement using the stove only. Heat goes up thru stairs and a vent register that I made. That way one can create a circular airflow: warm air that goes up has to be replaced by cold air coming down. If those streams are not sharing the same flow channel, it's more efficient (less turbulence).
Do put proper CO and smoke detectors in the basement and all floors (taking into account how the warm air/CO/smoke would flow when figuring out where to put them).

I'm still learning, but from my previous stove I know this can work. On Long Island (Eastern), so maybe a bit less cold that you, but my home may be well insulated, but not as good in the walls as yours.

Also check chimney requirements (length and dia needed for the stove you are looking at).

 

[stoveliker]

I now see @kennyp2339 s post above. He may have more technical knowledge, and what he says makes sense. I'm not contradicting him. So maybe listen to him more than me...

All I know is that I am happy with how it's going for me as I described.

 

[tabner]

I can't thank you all enough for the info. Very much appreciated. I don't think you guys are contradicting on the floor registers - it basically sounds like 'don't just think about hot air coming up, consider cold air sinking, and provide it the opportunity'.

I didn't mention it above, but your setup @stoveliker is exactly what I'd like to do long term. Get the solar panels to run the ductless system. At that point you're somewhat off grid, at least in theory, right? Solar for the summer AC, and wood in the winter? I'm jealous, that's a sweet setup.

@ABMax24 i suppose if i am having problem with draft/air intake, the green mountains do have an optional air intake kit, i could put one of those in and i'd definitely be good at that point?

 

[ABMax24]

@tabner I think it really depends on the situation. Generally if the existing fresh air intake into the house/furnace room is functional you should be okay. Of course depending on what your local code dictates for fresh air supply for a stove. One big plus is you have a tall chimney, basement plus 2 floors above, just like mine. Worst scenario you can crack a basement window and point a small propane torch in the stove and up the flue while lit for 30 seconds to start a draft.

 

[tabner]

Yeah, I read the fine print in the manual and for some reason I guess you can't terminate the air intake kit at a level above the stove. Being in a basement I'd have to run the air intake up to the height of the sill. So I guess that's a no go. I think I'll cross my fingers and worse case follow your window advice.

@begreen based on stovelikers setup, he's heating a house bigger than mine with a 50k btu unit. You mentioned I should go with the 60 over the 40 due to firebox size, but I should add that I only work 8 hour shifts and I come home for lunch, so filling the box frequently doesn't upset me too much. Would you still recommend going bigger is better?
My only concern is I want to be able to burn in the shoulder seasons without cooking myself out. Being in CT we have a lot of cool weather, but only a few weeks of what I'd call bitter cold weather.

 

[stoveliker]

I can't thank you all enough for the info. Very much appreciated. I don't think you guys are contradicting on the floor registers - it basically sounds like 'don't just think about hot air coming up, consider cold air sinking, and provide it the opportunity'.

I didn't mention it above, but your setup @stoveliker is exactly what I'd like to do long term. Get the solar panels to run the ductless system. At that point you're somewhat off grid, at least in theory, right? Solar for the summer AC, and wood in the winter? I'm jealous, that's a sweet setup.

@ABMax24 i suppose if i am having problem with draft/air intake, the green mountains do have an optional air intake kit, i could put one of those in and i'd definitely be good at that point?

I'm not off the grid because when the power is down, the solar is down too. (I have no batteries b/c I "use the grid as a battery" - I put them on in '18 when it was still the way that for 20 yrs I will have the meter run backwards when I produce more than I use (i.e. I don't get paid 7 ct when I produce and pay 22 cts when I buy, I get 1 kWh for 1 kWh b/c my meter runs backwards). As a result it did not make much sense to put a battery pack in. With a2.5 kW generator for a fridge, light, fan etc, I'm okay with power outages (as long as I can get gas).
But yes, I have almost no heating (free wood) and zero electricity cost. I still have the oil/hot water baseboard furnace, but I'm not using it now other than to heat my hot water. I was told that a heat pump water heater might work too. At that point getting rid of the oil business might be an option. For now I'm leaving it as is; it's a safe back up (oil tank is large), and I can run that system off my generator too.

Regarding sizing: the beauty of a cat stove is that you can really run it on a low power (low BTU output per hour). So as long as you CAN throttle its output down enough, a bigger stove is safer - you can heat a lot when you need to, but you can also heat a little when that's enough. Hence most folks use a BK 30 rather than a 20 - same lower limit, bigger box so longer burn times. I'm just starting with the BK (literally had 2 fires after the break in), but my first one got 22.5 hrs already.
So, check the low heat output limit of the ones you're looking at. If they are the same, go for the bigger one - b/c you can do more with that one while not compromising on the shoulder seasons with a low demand.

Just my 2 cents.

 

[begreen]

Yeah, I read the fine print in the manual and for some reason I guess you can't terminate the air intake kit at a level above the stove. Being in a basement I'd have to run the air intake up to the height of the sill. So I guess that's a no go. I think I'll cross my fingers and worse case follow your window advice.

@begreen based on stovelikers setup, he's heating a house bigger than mine with a 50k btu unit. You mentioned I should go with the 60 over the 40 due to firebox size, but I should add that I only work 8 hour shifts and I come home for lunch, so filling the box frequently doesn't upset me too much. Would you still recommend going bigger is better?
My only concern is I want to be able to burn in the shoulder seasons without cooking myself out. Being in CT we have a lot of cool weather, but only a few weeks of what I'd call bitter cold weather.

Yes, for 1600 sq ft in CT, a 2 cu ft stove is not large. In shoulder season weather you may be burning partial loads of fuel, then letting the stove burn out.

 

[kennyp2339]

Regarding sizing: the beauty of a cat stove is that you can really run it on a low power (low BTU output per hour). So as long as you CAN throttle its output down enough, a bigger stove is safer

Just and fyi not all cat stoves are created equal, it is quite unique the you can throttle down a cat stove with the BK brand leading that tech, second place would go to woodstock (now more so with there new air control) but most others dont use the cat or have the same placement of the cat for heat output, many brands place there cat solely for emissions purposes.

 

[tabner]

i can't thank you all enough for the input. I have the stove dealer/installer coming out this week just to walk the house and see if they agree with the potential heat flows, chimney condition and hookup, etc. As long as they give me the green light, i'm gonna go for it. I think you've all convinced me on the GM60 over the 40. I have several cord of firewood already split and stacked, and although a lot of it is 15" to 16", i know a good amount is 17" to 18" too, so it'll be nice to be able to fit that.

@Nigel459 from scanning the forum, you're the only person I can find with GM40 experience. Is it rude of me to ask if you'd chime in? Just curious what kind of space you're heating with the 40, is it more a room heater, or are you getting whole house heat, etc.

 

[stoveliker]

BTW @tabner, I read you were looking for a hyper unit (to heat when it's really cold outside. I thought about that, but given that I have a stove that can do that well, I opted to only go for the MXZ-4C36NA2. I believe it has still 22,200 BTU heating capacity at 17 F outside temp. I'm using it down to 35-40 F outside temps (b/c it's more efficient then with a max 43,000 BTU output).

My view was: why shell out a lot extra for a hyper unit when I have a "hyper stove" (whose BTU output does not depend that much on outside temps).

Just a thought before buying two pieces of equipment to cover extreme temperatures when one could (in principle) do. Of course I understand having a back-up in case one of the two fails is useful (though I note that wood stoves are pretty fail safe) - after all I still have that oil furnace - hot water baseboard too.

 

[tabner]

BTW @tabner, I read you were looking for a hyper unit (to heat when it's really cold outside. I thought about that, but given that I have a stove that can do that well, I opted to only go for the MXZ-4C36NA2. I believe it has still 22,200 BTU heating capacity at 17 F outside temp. I'm using it down to 35-40 F outside temps (b/c it's more efficient then with a max 43,000 BTU output).

My view was: why shell out a lot extra for a hyper unit when I have a "hyper stove" (whose BTU output does not depend that much on outside temps).

Just a thought before buying two pieces of equipment to cover extreme temperatures when one could (in principle) do. Of course I understand having a back-up in case one of the two fails is useful (though I note that wood stoves are pretty fail safe) - after all I still have that oil furnace - hot water baseboard too.

Thanks, i appreciate the extra input. I thought that too, however in order to use the chimney for the stove, i'll be completely disconnecting and probably selling the oil boiler, which means mitsubishi system will be my only backup. You're right the woodstove should be pretty fail safe, but i'm just not sure i can risk it, with a wife and two really young kids.
But it's a good suggestion, i'm going to ask my installer what the min temp difference is between the regular and hyper heat units, and also the price comparison.

 

[Nigel459]

@Nigel459 from scanning the forum, you're the only person I can find with GM40 experience. Is it rude of me to ask if you'd chime in? Just curious what kind of space you're heating with the 40, is it more a room heater, or are you getting whole house heat, etc.

Happy to chime in! I'm currently sitting in front of my GM40. Low air setting, some shoulder season pine in the box. Cat is active with small wispy candle flames, throwing great heat. Love it. I've had some looong burns with black locust. No problem going overnight even with this small box. I really like this stove more and more and I've used quite a few now... my promise to you is that I will post a full review, this week, now that I've been using it for over a year.

As for space heating vs whole house, all wood stoves are space heaters. Whether they can heat the whole house depends more on layout and circulation etc... of course with a good layout and circulation the stove output then factors in but I can tell you output won't be a problem in most cases with the GM 60...

 

[stoveliker]

Thanks, i appreciate the extra input. I thought that too, however in order to use the chimney for the stove, i'll be completely disconnecting and probably selling the oil boiler, which means mitsubishi system will be my only backup. You're right the woodstove should be pretty fail safe, but i'm just not sure i can risk it, with a wife and two really young kids.
But it's a good suggestion, i'm going to ask my installer what the min temp difference is between the regular and hyper heat units, and also the price comparison.

Sure, I understand. Redundancy makes me sleep better as well!
Be sure to ask not only the minimum outside temperature the systems can still function at, but ask what BTU heating capacity they have at that temp (and try to get an estimate of the BTUs your home, or part of it, needs at that temp); the lower the outside T the lower the heating capacity, even for a hyper unit (although the hyper unit of course will have a higher capacity at a given low T than a non-hyper unit).

 

[Highbeam]

You always want your central/thermostatic/primary heat source to fully do the job without you there. I think it is a mistake to cheap out on the proper heat pump just because you plan to burn wood when it's really cold. What happens when you want to go on vacation, your health fails, your wood stove fails, or you end up in jail unexpectedly. You and your insurance company should insist on the central heating solution being 100% capable.

If anything, undersizing the wood stove is slightly more palatable.

 

[stoveliker]

I don't disagree; for me the heat pump (for which sizing is not the concern here) *is* the secondary source. With wood first when it's cold, while having a second "first" (as in fully capable) in oil available.

The point about heat pumps as a first source when it's cold is that it gets expensive really fast. With the rates on Long Island and Connecticut. Unless one has solar.