Heating Super Insulated home from basement

[Elbinwyp]

I am seeking some help thinking through stove options for the basement of a super insulated home. We have been in the house for a year and determined that the basement needs some sort of a heat source to be comfortable enough to use.

The house is 1600sf ranch with a full basement. Open floor plan with open staircase in middle of house.
Peak heating demand of upstairs is ~18,000Btu/hr that is currently being met by a ductless mini split.
Basement has no heat source and has R15 on walls and under slab. Current temp is upper 50's. Im guessing the heat demand down there is ~5,000Btu/hr
House ventilated with an HRV
Basement is partially finished with intent to fully finish (bedroom and bath downstairs).
Stove in basement could be placed adjacent to staircase or one end of basement.
We receive significant solar gain during winter through south facing windows when its sunny.

I have two different philosophies on what a wood stove could do for us:

1) Put in a small, cheap stove (New Woodstock Survival stove) that would be fired hot and quick for times when we are downstairs. Would be strictly supplemental and could heat home in event of power outage. Down the road, a more constant source of heat could be added for more frequent use of basement.

2) Put in a Blaze King and adopt more of a whole-house heating approach.

So, my specific questions for those who have experience with stoves in an insulated basement:

If I put in a BlazeKing and load the sucker up for a low and slow burn, lets say 12,000Btu/hr, will I be absolutely roasting downstairs, or will enough of that head migrate upstairs that it will remain comfortable over that period? I also have some concerns about the lack of constant heat demand of our house due to the solar gain.

@begreen I have seen your name on a bunch of threads related to this topic. I would be curious of your take.

 

[DickRussell]

I have relevant information for you. My house, in central NH (CZ 6), is superinsulated, somewhat larger with two levels on a 2,000 sqft footprint, set into a hill so that foundation wall is full height uphill and totally walkout downhill. Foundation walls and lower level slab have R20 foam. Heat loss model said design loss at 70 degF delta T would be 22,000 BTU/hr, but best I can calculate from a long cold spell is closer to 19,000. Main heat is via GSHP, two ton, 25,400 BTU/hr maximum from mfg tables at operational air and water flows. But it keeps the house at 70 F in just first stage, even in the recent bitter cold spell. The warm air distribution is via three zones, two up and one for the lower level.

I do have a small woodstove in the lower level, a Quadrafire 2100 Millenium, from which (according to the tag on it) I can get 11-28 KBTU/hr. In the 2010-11 winter, that small stove actually kept the house in the mid 50s, perfect for the crew finishing the interior, burning just part time. I'd start it up mid afternoon, add more wood every two hours, and load the last around 10 to 10:30pm, letting it burn out after that. No interior doors had been hung, and the heated air from the stove would travel across the ceiling and up the stairwell. Thermometers in the utility space across the floor from the stove and well away from the stairwell upstairs consistently read within a degree of each other. The heat pump wasn't put into operation until the end of the winter. I selected that particular stove partly because it was small, with heat output bracketing the design heat load of the house and partly because it had provision for direct connection of an outside air duct. I didn't want an open duct dumping raw air into the house long after the fire burned out. I rejected one stove because, according to the mfg in a phone call, an air duct would just have to dump air "into the vicinity of the stove."

In actual use, after completion of the house, we fire up the stove late in the afternoon (5-7pm) and keep it going through the late news. Then it just burns out overnight. We leave the thermostat down there typically at 65, but after an hour or so the stove has brought that up to a comfy 70 or so. When it gets to 71-72, we leave the stairwell door open and let the excess heat go up. There is enough mass to the walls, slab, and interior stuff on the lower level that the temperature down there doesn't soar to uncomfortable levels over the 5-7 hours of operation. I suspect that a larger stove would overheat the place easily. Nor is having the stove across the room from the stairwell a problem with getting the heat distributed upstairs when needed. Bear in mind that with a superinsulated house, the heat source doesn't have to be located as carefully as with "ordinary" construction. The heat distributes itself quite nicely, since it can't escape the house easily.

My recommendations? Don't put a big stove into a superinsulated house. Go small. Assuming your house is tight enough to warrant having an HRV (ours is/does), give some thought to having an outside air duct supply air to it. That may call for locating the stove close to an outside wall, to keep the duct short. Insulate the duct, or it may sweat. If the foundation is full height all around, so that the duct would have to come in from up by the sill, that may be a problem wrt reverse drafting. But the air requirement of a small stove is fairly small, so that whatever low level of air leakage the house has may be sufficient. I should mention that when I light the stove I have to be sure the dryer and range hood are off, or I get backdrafting and have to open a nearby window for a while until good draft is established. The stove is not 100% airtight, and smoke leakage is possible even with the direct connection of the air duct. Once good draft is established, I can run the dryer and range hood, although the highest range hood speed might be a problem. Anyway, running the stove may simply result in the HRV air flow (in/out) running out of balance, which is fine. Hopefully you can locate the stove such that the chimney can be run up through a chase carved out of a closet or set into a corner of the upstairs.

PS. If you plan to have a bedroom downstairs, code will require a means of egress in case of fire. That calls for a door to the outside or a window of a certain size. If the foundation is full height all around, you'd have to excavate outside, cut a chunk out of the foundation for the window, and provide both drainage of the window well and a means to climb out of the well.

 

[peakbagger]

I have talked to a few folks with super insulated homes and they advocate the smallest stove possible. Something the size of Jotul 602. Basically a short fast burn when needed.The issue that does arise with supertight homes is that the buildings just wont allow the stove to draft unless the HRV is running and balanced correctly. HRVs need to be adjusted for flow and pressure drop during commissioning of a house which should occur after the house is complete, unfortunately the concept of commissioning a home is foreign to most contractors or homeowners. Check the manuals on any HRV and there usually is a recommendation to flow test and balance the system but expect few folks do it. I expect the contractors tend to bias it towards excessive exhaust.

 

[prezes13]

I would go with BK stove. It will give you the low btu burn I will get from a small tube stove if not lower. It will give it for much longer time there for it will be more useful. Bonus you will be able to crank up high btus if the need arives.

 

[fstbck6706]

I have a ~1500sq foot cape cod with a Woodstock Ideal Steel in the basement.

Basement: Half has R5 insulation / Half has zero insulation / Slab has zero insulation
First Floor: Zero insulation (That's a future project)
Second Floor: Fully insulated.

I run the Ideal Steel 24/7 in the winter with the air slightly over 1/4 open. I use the furnace fan to suck the air from the basement and distribute throughout the house (fan runs about 15-25 min per hr depending on temp). It works great and can easily overheat the house when the weather is near or above freezing.

I end up with average temps of:
Basement: 80-85
First Floor: 68-75 depending on outdoor temp
Second Floor: 68-70

With your very well insulated house I would not want a stove as big as mine as I feel like it easily would overheat the house. My house has heat escaping left and right and is still very comfortable (until it gets to about 15 degrees outside).

 

[Elbinwyp]

Great replies. I appreciate everyone's input. I have placed a deposit on the Woodstock Survival stove and am working with an installer on the details of the chimney run. I will be sure to report back with my experiences.

 

[Elbinwyp]

Following up on this. I just walked through the install with my contractor and have cold feet. I am struggling to understand one key component. We have a spot in the basement chosen for the stove. The pipe will transition to Class A DuraTech at the basement ceiling, run through a first floor closet (will be enclosed in a chase), and then go through the attic to the roof.

My concern is that the installer said several times that there will be an air gap around the pipe at each floor and roof crossing that will allow air to flow around the pipe up through the attic. Functionally, this seems like it renders my airtight building envelope far less functional by having an open hole through my ceiling plane.

Is this a standard install? Is there any way to avoid this opening? And if not, is this a legit enough concern to abort the mission and instead install a ductless minisplit?

@begreen I feel like i have read a few posts of your on other threads about how to handle the airflow in this chase.

 

[begreen]

There must be a firestop at each ceiling penetration. The first at the basement ceiling will be achieved by the chimney support box, no leakage there. In the attic there will be a firestop+attic insulation shield. Slight leakage is possible there, but not much if any. You will have to have fresh air exchange in the house anyway so I don't think this is of major consequence. You might call DuraTech support and ask if they have an insulation kit or if kaowool insulation could be used around the chimney pipe in the attic insulation shield. There will be a small air gap at the roof flashing.

Here is an illustration. Go to the DuraVent website and download the DuraTech installation guide. It will help you communicate the proper requirements to the contractor.

 

[Knots]

I don't know about "super-insulated", but I have a 1400 sq ft ranch with 2x8 walls and fully insulated foundation walls. The house is tight and I have an ERV. Attached garage on one side and two-bay under part of the house.

I have a Jotul F55 in the center of the basement near the stairwell with a class A straight up.

In the middle of winter hear in Maine, my routine is this:

- wake up early and the house is around 55F (I like to sleep cold).
- pack the cold stove with hardwood and fire it up. It takes around 5 hours to burn that load.
- house gets up to 72F. Garages stay above freezing. If it's real cold (below 10F), I might burn a partial load in the afternoon, otherwise it might get too warm come bedtime.

Some pics to show chimney below. 2nd pic is roof hole (contractor was a little sloppy here). 3rd and 4th are pipe through chase in 1st floor closet.

 

[Ashful]

It always amuses me that chimney installers get skeevy about working on my 250 year old house, and throw all sorts of concerns about a chimney that’s been used consistently for two and a half centuries, whereas I look at these photos of modern houses and they scare the chit out of me. So much wood around a double wall metal pipe just feels wrong.

Every year I am the witness to a few unfortunate fires, also always almost new houses, usually on cold days when the power goes out and folks fire up their wood burning appliances.

 

[begreen]

One of the reasons one doesn't see a lot of 250 yr old houses around it that many burned down due to poor chimneys and installation. Lots of chimneys had local solutions to brick and mortar of varying qualities. Some were good, some were not, and some were just lucky. There were sloppy builders and installers and maintenance back in the days of yore too. As soon as better heating solutions came about many of those old chimneys and fireplaces sat idle. And that is in places where the ground doesn't move much. The fact that someone hadn't burned down our house during the 1970s oil embargo is amazing. After disassembling an 85 yr old fireplace with crumbling mortar and two barely plugged take-offs - in an earthquake zone, I'll take a properly installed, tested metal chimney to masonry any day.

 

[Ashful]

All true, begreen. Part of my point is that, if it hasn’t burned down already, after 250 years of continuous testing, it is likely a fairly safe design. Modern codes be damned!

Our great-great-great grandkids can argue over which was actually better, when these particleboard houses reach the quarter-millennium mark.

 

[yooper08]

Curious on location you chose with the small stove? Did you go with the end or by the stairwell?

I know I'm late to the party here but if the main goal is to heat the basement, I would put it on the end. I also heat from the basement and the main goal was to be the heat source so we could use the space in the winter, plus my office is down there (work from home). We do get quite a bit of heat upstairs still.

 

[Knots]

It always amuses me that chimney installers get skeevy about working on my 250 year old house, and throw all sorts of concerns about a chimney that’s been used consistently for two and a half centuries, whereas I look at these photos of modern houses and they scare the chit out of me. So much wood around a double wall metal pipe just feels wrong.

Every year I am the witness to a few unfortunate fires, also always almost new houses, usually on cold days when the power goes out and folks fire up their wood burning appliances.

...it is likely a fairly safe design.

The clearances of the Class A in my house exceed the manufacturer's specs. I have a removable panel in the closet for the chase so I can inspect easily. While running the stove hot with a load of oak, I checked temperatures in the chase and in the attic all around the chimney with an IR thermometer. Everything was low. I sleep like a baby with the stove going.

You may have a good design, but if it isn't maintained and inspected, it will degrade. I deal with turbine engines that are a proven safe design, but fail due to lack of maintenance or other environmental factors.

My concerns for mine deal with how he cut the hole in the roof and sealed it, but I'll fix that up. Right after I inspect my chimney for the season...

 

[Ludlow]

From the pic it doent look like that stubbed off rafter is 2" from that pipe. Id say 1-1/4". Dont know why they didnt just pull that orphaned piece off the nails. Its of no use anyway.

 

[begreen]

I checked temperatures in the chase and in the attic all around the chimney with an IR thermometer. Everything was low. I sleep like a baby with the stove going.

I left mine exposed for a year so that I could check temps. No worries here either. Some houses are at greater risk from boiler pipes running through joists and floors than with a properly installed chimney.

 

[Ashful]

I left mine exposed for a year so that I could check temps. No worries here either. Some houses are at greater risk from boiler pipes running through joists and floors than with a properly installed chimney.

View attachment 229035

Yikes! Oil-fired boiler with miles and miles of 3/4" copper feeding baseboards, here.

 

[Knots]

View attachment 229030

From the pic it doent look like that stubbed off rafter is 2" from that pipe. Id say 1-1/4". Dont know why they didnt just pull that orphaned piece off the nails. Its of no use anyway.

Yeah - it's in the chase on the first floor that I was worried about and the clearances are exceeded there. The attic is cold and I've been up there when the stove is running full tilt. I can place my hands on the pipe there. That's about 25' above the stove.

Yes - I'm going to pull those stubs off and box that better. The contractor for the house failed to coordinate the center of the chase with the rafters. Duh.

 

[Ashful]

The contractor for the house failed to coordinate the center of the chase with the rafters. Duh.

1x3 fir “rafters”?

 

[Knots]

Ummm...no. That's the local stuff for the chimney. Shouldn't have called it rafter. 90 psf roof.

 

[Elbinwyp]

There must be a firestop at each ceiling penetration. The first at the basement ceiling will be achieved by the chimney support box, no leakage there. In the attic there will be a firestop+attic insulation shield. Slight leakage is possible there, but not much if any. You will have to have fresh air exchange in the house anyway so I don't think this is of major consequence. You might call DuraTech support and ask if they have an insulation kit or if kaowool insulation could be used around the chimney pipe in the attic insulation shield. There will be a small air gap at the roof flashing.

Here is an illustration. Go to the DuraVent website and download the DuraTech installation guide. It will help you communicate the proper requirements to the contractor.
View attachment 228963

@begreen , this is great. I have spent some time on the DuraTech site and it appears the firestop radiation shield has a cut out to fit the pipe snug and should result in minimal air leakage. I am still perplexed at where in the install my contractor is talking about this "gap" that would cause significant air leakage but am now more educated to talk this through.

My other main concern was running my outside air kit through my rim joist. I currently have 3" of rigid foam insulation on the exterior of my rim joist. The plan would be to cut a 4" hole (Woodstock built a 4" outside air kid adapter on my stove. See attached) and run a combination of insulated rigid and flex pipe through my joists, over to the stove about 15' away and drop down to connect to the stove. Its not going to be pretty but im not sure I have any other options. If this is insulated and sealed well enough, I should be able to avoid condensation on the interior of my rim joist. Should I worry about this sitting open all year long? Is there an elegant way to plug this or to install some type of valve to close it when not using? Is this an overblown concern?

 

[begreen]

The bigger concern is a direct connection to the stove when the OAK is much higher than the stove. The concern is draft reversal, especially when the stove is running very low. One doesn't want the OAK piping to become a chimney.

 

[webby3650]

DuraTech flashings are ventilated. There will be free air around the pipe in this location.