How hot before turning stove down

[ronsomething]

Fitting a wood stove to a super-insulated ICF house isn't easy. There's not much guidance out there. I have a new Lopi Evergreen stove (with legs) 12,000 - 70,000 BTUs. I have a new construction ICF house with finished basement, main floor, and 2nd level. Each level is 1280 square feet for a total of 3,840 sq feet. The stove will be on the main floor in the family room/great room on an exterior ICF wall. The main floor is basically divided in two by a load bearing wall, making the family room/great room about 640 sq feet. My concern is that the stove is going to cook us out of the house. I may need to get a different stove. I like the soapstone stoves, but I'd rather not have a CAT, which leads to my questions:

1. Is anybody aware of a soapstone non-CAT wood stove? What are these so-called "hybrid" stoves? Do they have a CAT and a secondary burn chamber? I really prefer a non-CAT stove, but am open to persuasion otherwise.

2. The Lopi stove has a wide range of BTUs 12k-70k. I understand the stove is likely less efficient in it's lowest range, but would probably function ok I'm guessing in the 18k-25k-ish range. Do I first have to fire the stove up really hot 50-60-70k BTUs, get a big fire going, before turning it down? Or can I turn it down to the 18-25k BTU range early in the burn cycle before the house gets too hot. I'm thinking that if I can turn the stove down before we get too hot, then this stove might be ok, otherwise I probably need a different stove.

3. Alternatively, I am considering putting soapstone on the rear wall and hearth, which, in my thinking, may even out the heating somewhat. Would this be helpful?
Thanks for your replies!!

 

[begreen]

The Evergreen may work out ok. You control the size of the fire by the amount of fuel and air the fire gets. 2500 sq ft is a large area to heat. How open is the floorplan to the stove room? Post a sketch if you can.

What is the primary heating system in the house? What is the BTUs output rated at?

 

[ronsomething]

Thanks for your reply @begreen. My house seems to be pretty well insulated, just moved in a couple months ago, so I'm still keeping my eye on things. During the day we keep the main floor about 68-70 degrees, and turn it down to 60 degrees at night. When I get up in the morning, the thermostat is often above 60 degrees, meaning the furnace didn't kick on at all during the night, even though it was single digits to low teens during the night. I think that's pretty good. In addition to the ICF walls, I air sealed using the techniques I learned on buildingscience.com, greadbuildingadvisor.com, and Matt Risinger YouTube channel.

In response to your questions:
1. It's an open floor plan, see attached. I didn't diagram the basement, but it's about the same as the main floor but there's a bathroom in place of the kitchen...roughly. Is the basement square footage not counted (because heat rises)??? With the basement my house is 3,840ft, but you referenced 2,500ft in your post, which would be the square footage of two levels.

2. I have two furnaces. One is in the basement mechanical room which heats the main floor and basement. It's rated at max output 100,000 BTUs. I don't know if the HVAC installer derated it for my elevation, i.e. installed smaller gas orifices. It says it's supposed to be derated 2% per 1,000 feet above sea level. I'm at 6,000 feet (central Utah), so derated output should be 88,000 BTUs. There is a smaller (non-condensing) furnace in the attic which heats the upstairs, max output 80,000 BTUs, or 70,400 BTUs after derating. The 99% design temperature is 4 degrees. The average low temp in Jan is 16 (but I think it's been a lot colder than that this year haha)

Ok I guess I understand that I can build a smaller fire in the stove (i.e. less wood) so it doesn't over cook us, but then I have to add wood more frequently, and I won't get an overnight burn. The specs say I should get up to 10 hour burn time, but I'm assuming that's on a full load.
I was hoping to fill up the firebox (2.2 cu ft) with wood, get it rolling good (without burning us out), then turn it down for overnight burn. My concern is that it's going to get very hot on the main floor while the stove is getting up to temperature before turning it down. The owner's manual says to let it burn for at least 15 minutes before turning the air down. Would a smaller stove be better, e.g. 50-55k BTUs?? Or do I get the same thing if I put in say a couple less logs (i.e. 55k BTUs worth of wood), get it burning good, and then turn it down??

FWIW, I attempted to do a heat load calculation/heat loss analysis. I used 4 different calculators online to cross check my work. The average is 32,000 BTUs. So, the Lopi Evergreen is potentially over 2x BTUs.
In my calc, I only included the square footage that the wood stove would reasonable be able to heat, i.e. all of the main floor, most of the second floor, and a fraction of the basement. I would like to use the wood stove as my main heat source (as much as is reasonably possible) and supplement with the furnace, as needed. There is an air return 12 feet away and another 16 feet away from the stove, so I should be able to circulate some of that warm air throughout the house on "fan only" mode. There's no insulation between first and second floors, so I think I'll get some heat percolating up through the floor.

So.........the question is.........smaller stove? Alternatively, would some kind of soapstone back wall and hearth even out the temperature swings??? I appreciate your consideration and input, as I try to figure this out.

Thanks for listening

 

[begreen]

That's a pretty big space and a lot of BTUs in furnace heating power. The open floorplan and stairwell will help heat convect well. If a longer burn time is desired I would be looking at the Endeavor or Liberty in the Lopi stove line. If you want more low-output power look at cat stoves from Blaze King, Kuma, Regency, and Woodstock. Or for more even, soapstone-like heating look at the cast-iron jacketed Pacific Energy Alderlea T5 or T6 stoves.

 

[spuldup]

I appreciate your studiousness, @ronsomething!
Stove btu ratings are not to be compared to fossil fuel furnace ratings. Burning wood is largely an uncontrolled enterprise. Stick with your current unit and figure it out. Should you make a misstep, you have ample fossil fuel alternatives to keep you warm. Better to have too large a stove than too small (to a degree).
Love the floorplan. The office I type this in is about your size and it's just right IMO.

 

[EatenByLimestone]

I think your furnaces are oversized for your home if your heat calcs are accurate.

How tall is your chimney? Due to your altitude, it’s going to make a difference in your stove selection. I’d stick to a medium sized stove around 2cu ft in size.

If the stove is on the 1st floor, I don’t see it doing much for your basement.

 

[bigealta]

I don't think you will be "cooked out". Simple enough to adjust your burning to what temp you need/want in that house. You can also open and close room doors to dump extra heat into those rooms (both upstairs and downstairs), or close them to keep more heat in the large living room.

Also you can have anywhere from 1 smallish fire a day to burning 24/7.
1 good size fire a day is not going to cook you out. Especially if it's in the morning when inside is close to 60F.
Many of us get our woodstove rooms to 80F or even higher and it can be Very Nice!

 

[vbu]

Many of us get our woodstove rooms to 80F or even higher and it can be Very Nice!

I second this! Gets the missus in the wardrobe I prefer her to wear

 

[ronsomething]

I really appreciate your feedback...tons! (@begreen @bigealta @vbu @spuldup @EatenByLimestone ).
I'm going to take a quick look at the Lopi Liberty and Endeavor, as well as the PE Alderea lineup to see if there's clear and convincing evidence to overturn the flag on the play . I appreciate the suggestions @begreen.

In reply to your comments/questions @EatenByLimestone... I hear what your saying about the furnace sizes. I'm pretty sure the HVAC contractor just did what he always does, used rule-of-thumb standards, without taking into consideration the fact it's an ICF houses with pretty good air sealing. I'm not confident he did any sort of J calc, heat load/loss calc etc. Compared to my previous house, the main furnace (which is a two-stage furnace) during the day seems to kick on as much as or even a little more than my past experiences, and my house is way! tighter than any house I've ever had. It comes on probably 3-4 times per hour and runs for about 10-12 minutes, then kicks off. I live in a very small town and county, I think the HVAC guys aren't super sophisticated??? I'll address it down the road if I have to.

Regarding my chimney height...from the floor of the main level where the stove will be placed, to the exit point on the roof is 31 feet. It runs up within the interior of the house and up into the attic and out the roof (vs on the exterior of the house). I'm pretty sure it's triple wall, cost a fortune. What issues do I need to be aware of, @EatenByLimestone?

 

[begreen]

I'm pretty sure it's triple wall, cost a fortune. What issues do I need to be aware of, @EatenByLimestone?

Check and see. The chimney is infrastructure and triple-wall class A pipe is the cheap stuff. I strongly recommend double-wall class A pipe instead for better service and longer life. It also is smaller in diameter so it takes up less space.

 

[cahaak]

Your furnaces are vastly oversized. Make sure you have an outside air intake kit for the stove.

 

[EatenByLimestone]

When furnaces are oversized, they short cycle. They put out so much heat that after only being on a few minutes, they are forced to turn off. The constant on and off causes parts to break. It's good you're putting in a stove. It'll keep them off longer!

That's a tall chimney, it should really draw well. Once you figure out which stove you want, it might require some fiddling to get used to the draw, but maybe with the altitude canceling part of that height out, it'll be mild mannered! I agree with BG that double walled would be the way to go, but since its already in...