Sizing a wood stove for a super insulated house.

[Floydian]

Hello Folks,

I am hoping for some input on my situation. Here it is:

I have built a new 2200 sq ft home for my parents. 1100 sq ft basement(half walkout) and 1100 sq ft first floor. Both levels have an open layout and the wood stove will be centrally located in the basement right next to an open staircase.
22 feet fo centrally located Class A chimney is a straight shot up from the basement ceiling to 3' above the roof peak.

The house is very well insulated(especially for our climate). R15 below grade, R30+ above grade walls, R60 attic,
R5 triple pane windows, well air sealed(no blower door test yet) with an ERV for balanced ventilation.

The design heat load of the house is under 20,000 btus/hour and the average heat load is less than half of that.
The first floor has a mini split heat pump as its primary heat source. The basement will either get its own mini split or it will have electric resistance heat as needed in the future.

The wood stove will be primarily for backup during power outages and to help out during the colder weather. I cant see them burning more than half a cord of dry wood a year as the house shouldn't need more than 20 MM btus/year for heating. ALWAYS dry wood, I know.

I want a stove that can take an OAK if needed but for now I want to take the "wait and see" approach.

All this rambling leads me to this, I really like the Englander 17-VL and so do my folks but I can't find one anywhere close so we can see the thing in person before buying. (Likely from Home Depot-Grrrr)

So I am asking, do you all think this little 17-vl is a good fit for what my folks are looking for?

It is my opinion that we can throw out the square footage ratings and just look at the btu output but this is my first experience sizing such a small stove for a relatively large space.

I welcome any and all opinions on this subject,

Thanks,

Noah

 

[drumbum]

Go for a 30 unless you're trying to put it in closet.

 

[begreen]

This is a super insulated house. It has very different heating requirements. At the specced btu requirements the 30 would be very serious overkill.

Most important is how your folks want to use the stove. Do they want it for occasional fires and power outage heat or do they want to burn 24/7 in the winter? The 17VL would do the job but it is only going to be good for a 4 hr burn. It would be good for the occasional fires scenario.

However, to get a low steady btu output burning 24/7 they will need a cat stove. A BlazeKing Chinook 20 looks like a nice fit if they want a contemporary look. It's capable of a steady low 12K btu/hr fire. Or perhaps a Woodstock Keystone?

 

[Floydian]

Hi begreen,

Most important is how your folks want to use the stove. Do they want it for occasional fires and power outage heat or do they want to burn 24/7 in the winter.

Definitely not looking for 24/7 burning. Power outage is the most important aspect followed by occasional fires when colder weather sets in. I feel OK with the short burn times as the house really wont lose much heat in a 4 or 5 hour time frame. My folks have plenty of experience burning wood but we understand they will have to adapt to some different techniques with this new house.

However, to get a low steady btu output you will need a cat stove.

Can these stoves really be dialed down as low as they claim and still operate near peak efficiency? This would have some appeal and allow them to burn more wood without cooking themselves out of the house! The BK Chinook 20 is a nice looking stove. Any idea of a ballpark price?

Then I would have to sell my folks an a cat stove which could be challenging!

Thanks,

Noah

 

[begreen]

Yes, a cat stove can be dialed down. BK is pretty conservative about their ratings. They say the Chinook 20 will burn for 20 hrs at a low rate. The pitch is easy: BK stoves don't have the typical temperature swing throughout the burn cycle. They provide hour after hour of steady heat with thermostatic regulation as long as you feed it dry wood. I don't know the price, but it will be much more than the 17VL. I would guess closer to the $2K range. I think their Sirocco 20 is less expensive. Call several local dealers for the best price if interested.

 

[DickRussell]

I'll add to what Begreen said. Yes, for a superinsulated house, disregard whatever square footage numbers the stove mfg provide. Go by the range of heat output provided vs what you calculate as a design total house heat load. Figure you can use a stove that is rated for perhaps 50% over design heat load, although at times it may be run at the lower end of the tag range (smaller fires), and that it likely will be allowed to burn out overnight. The thermal mass of the house will absorb a fair amount of heat over multiple hours of burning, with the door to the upper level open. Bear in mind, too, that a house like this will lose heat very, very slowly, even when it's bitter cold outside.

For reference, I have a superinsulated house, also on two levels (lower half walkout), although the footprint is just shy of 2000 sqft (in central NH, CZ 6). The calculated design heat load is 22,000 BTU/hr at a delta T of 73 degrees, although it appears that the actual is a bit less. It's hard to say, but given that the house loses heat so slowly that the effect is to dampen the peak delta T. The house never is in true steady state. The house is heated by ground source heat pump, and by differencing on the winter electric KWH usage vs shoulder seasons, the heating cost is close to or below what was calculated. I've been told by an area builder of superinsulated houses that in his experience the actual rate of heat loss tends to be lower than the heat loss predictions indicate. In my case, the heat pump tables show an output of 25,400 BTU/hr in second stage, but about 76% of that in first stage. Through the winter, the unit keeps the house comfortably at 70 F in just first stage, and not running all the time at that.

I selected a woodstove for the new house from what was available from the local stove dealer. I rejected a small Jotul, as it did not have provision for direct connection to an OAK. The vendor, when contacted by the dealer, said that an outside air duct would be terminated "in the vicinity of" the woodstove. I didn't want an open duct dumping raw air into that area overnight, after the fire had died. Instead, I picked a Quadrafire 2100 Millenium. This stove had a tag firing range of 11-28,000 BTU/hr, which sort of bracketed the design heat loss of the house. It also had a place on the back of the stove for direct connection of an outside air duct. I installed the stove on the lower level.

During the 2010-2011 winter, when the shell of the house was up and the inside work continued, this small stove heated the entire house, which is considerably larger than in your case (close to 4,000 gross sqft), although with R20 subslab and foundation wall insulation, and R40 whole-wall insulation where framed (both levels), and R60 attic floor, plus triple pane windows, and blower-door verified air leakage at 0.8 ACH/50. During that winter, I started up the stove mid-afternoon and fed it wood until about 10pm, letting it burn out after that, some time after midnight. With this part-time operation, that stove kept the house in the mid-50s, perfect for the crew there during the day. In terms of heat output vs house heat loss, the numbers fell into place fairly well, with a lot of room for error in those numbers.

After two full winters of living in the house, we have found that we like to have a fire burning in the stove in the evenings when we are down there watching TV. The door has a large glass window, which lets us watch the fire. After an hour or so, with the door at the top of the stairs closed, the lower level temperature has climbed a couple of degrees or more. After that, if we keep it burning, we can just leave the stairway door open, and the upper level temperature slowly climbs, keeping the heat pump from coming on. We can't keep this up more than 5-6 hours, or things would just get too warm inside. But that's fine, because by then it's time to go to bed anyway. If you are a wood burner at heart, having a superinsulated house is nice. You just don't have to think in terms of needing an overnight burn.

 

[PassionForFire&Water]

I advise to look into a hydronic wood stove: free-standing or fireplace insert.
Ratio 30/70; 30% radiant heat, 70% in to the water thermal storage.
You design the volume of the thermal storage so it heat the house trough the night via the energy in the thermal storage, so you don't need to fill the wood stove.

 

[Floydian]

Great info DickRussell!

I have read some of your posts over at GBA and appreciate you taking the time here.

I rejected a small Jotul, as it did not have provision for direct connection to an OAK.

I too was dissuaded with the proximity air with the Jotuls though I do like that little 602. Oh well.

I didn't want an open duct dumping raw air into that area overnight, after the fire had died.

I don't want this either. My concern is not as much about make up air for the wood stove as it for the dryer/range hood. Did you provide make up for these or do you not worry about it with the OAK?
As I said, I am going to wait and see how things work without the OAK once the wood stove is in place. I anticipate cracking a window for either the dryer or range hood regardless of whether or not the wood stove is in operation. And I will be ready to add the OAK in the future if needed.

The comfort level on the first floor in the house is really fantastic with just the point source mini split. I am really into this super insulating thing but most clients probably wont be quite as easy to sell on the idea as my parents!

Again, Thanks!

Noah

 

[Floydian]

Thanks Marc,

I advise to look into a hydronic wood stove: free-standing or fireplace insert.

I strongly considered this route and I am thoroughly aware of the benefits of thermal storage and low temp radiant. I do love me some wood fired hydronics but for a super insulated house on a budget I feel that money is better spent on the enclosure allowing for simpler heating systems. If money was no object for my folks you have several options that I would be very interested in and I will keep them in mind for any upcoming projects. I just find it hard the beat the mini split, wood stove combo for overall cost and performance.

Noah

 

[BrowningBAR]

Hello Folks,

I am hoping for some input on my situation. Here it is:

I have built a new 2200 sq ft home for my parents. 1100 sq ft basement(half walkout) and 1100 sq ft first floor. Both levels have an open layout and the wood stove will be centrally located in the basement right next to an open staircase.
22 feet fo centrally located Class A chimney is a straight shot up from the basement ceiling to 3' above the roof peak.

The house is very well insulated(especially for our climate). R15 below grade, R30+ above grade walls, R60 attic,
R5 triple pane windows, well air sealed(no blower door test yet) with an ERV for balanced ventilation.

The design heat load of the house is under 20,000 btus/hour and the average heat load is less than half of that.
The first floor has a mini split heat pump as its primary heat source. The basement will either get its own mini split or it will have electric resistance heat as needed in the future.

The wood stove will be primarily for backup during power outages and to help out during the colder weather. I cant see them burning more than half a cord of dry wood a year as the house shouldn't need more than 20 MM btus/year for heating. ALWAYS dry wood, I know.

I want a stove that can take an OAK if needed but for now I want to take the "wait and see" approach.

All this rambling leads me to this, I really like the Englander 17-VL and so do my folks but I can't find one anywhere close so we can see the thing in person before buying. (Likely from Home Depot-Grrrr)

So I am asking, do you all think this little 17-vl is a good fit for what my folks are looking for?

It is my opinion that we can throw out the square footage ratings and just look at the btu output but this is my first experience sizing such a small stove for a relatively large space.

I welcome any and all opinions on this subject,

Thanks,

Noah

I envy you.

That being said, if this were my home, I would look at the Pacific Energy T4 or T5, the Blaze King Princess, Sirocco 20 or Chinook 20, and the Woodstock Keystone or Fireview.

All of which will give you longer burn times and softer heat for your situation. That is what I would look at. I have no problem or issue with teh Englander 17-VL, I just do not know enough about it to say it would meet my needs for your situation.

 

[begreen]

I have a little experience with a super insulated house owned by a relative. They heat their place through most of the New York winter with just a homemade wood fired pizza oven. It's silly how little heat it takes to keep the place comfortable.Their average wood consumption for a 2300 sq ft home is under 2 cords/yr.. Insulation, sealing and thermal breaks really do work.

 

[BrowningBAR]

I have a little experience with a super insulated house owned by a relative. They heat their place through most of the New York winter with just a homemade wood fired pizza oven. It's silly how little heat it takes to keep the place comfortable.Their average wood consumption for a 2300 sq ft home is under 2 cords/yr.. Insulation, sealing and thermal breaks really do work.

Lucky bastards.

 

[begreen]

Not lucky, they planned it this way, designed and built their own house. They have been saving since 1982 in this home.

 

[DickRussell]

Noah, the house has an HRV, which is run full time on lowest setting. There is no makeup air for either the dryer or the range hood. What happens when either of those two is running is that the resulting house depressurization makes the HRV go out of balance. One thing I have to be careful about, though, is not to have either running when I start up the woodstove, or it backdrafts, likely pulling combustion air and flue gas through the stove and past the door gasket. Once it's blazing and the flow from the OAK and the hot flue gas going up the chimney are established, I can run either dryer or range without a problem. I do wonder about that range hood on its highest speed; that might need a nearby window cracked open.

In your case, cracking a window a bit probably will be ok if you have the dryer or range hood running along with the woodstove. With neither running, the house, tight as it may well be, probably still leaks enough to provide the combustion air needed for a small woodstove, which I have read is only around 40-50 cfm. I guess you'll know on the first burn.

 

[Floydian]

Thanks to everyone for posting.

At this point I think we are going to give the 17-vl a go. The price is a good fit for where my folks budget is at for now. Once they have sold their current house they will have the means to upgrade if they feel the need or want.

I will try to remember to give an update on how the stove works once its up and running.

Noah