Ideal floor plans for wood heat?

[begreen]

Build it well with lots of insulation and there's no need for wood heat.

This Maine home can stay 70 degrees without a furnace, even when it's freezing outside

With extra insulation and lots of sun, a passive house in the town of Hope is able to maintain an indoor temperature of around 70 degrees without the use of a furnace.

www.mainepublic.org

 

[peakbagger]

I think that design would violate the previously stated windows preference.

Based on the course I took last year, their estimate of 40K additional is very optimistic for an official Passive house. There is lot of paperwork and third party auditors and inspectors that need to be involved with certification. Skip the paperwork and the coveted certification does not get issued at the end of the project. I really do not think from a resale perspective in most markets that a premium paid to build a certified Passive House will be recovered compared to an uncertified house built to Passive Home or zero net energy standards.

 

[Nate R]

"just a small heat pump, no furnace." <--- That's vague. I'd love to know what their cooling and heating loads look like in reality.
Kudos to them for not building a giant house, sounded like a reasonable size for their needs.

 

[tlc1976]

Lots of sun is the key. Winter sun makes a big difference for me too, but living near the Great Lakes I hardly get any.

 

[peakbagger]

Most passive homes I have read of regionally end up putting electric duct heating in the supply air to the house from the Heat Recovery Ventilator (HRV). One thing that is very hard to factor in is an externally vented kitchen hood, anyone who has lived with the hood that just recirculates air to the room though a filter rather than outdoors are probably aware, that the are one step away from useless. The exhaust can not be run through an HRV as it will plug it quickly so testing is generally done wen an externally vented unit is not being used. Wehn used the duct heater in the HRV will end up supplying makeup. A minisplit does not work as well as it does not have outdoor air makeup.

One design aspect folks forget to factor in is the thick exterior walls. Note the 15" walls in the article. This eats up a lot of interior space unless the building footprint is upsized (hihger property taxes as they are typically based on exterior footage. Many folks find the window arrangment as odd as the windows wells have substantial depth compared to conventional wall. The super high efficiency Euro windows are slick rigs but very pricey and currently imported from Europe. Very long lead time and generally they have very specific installation requirements that take contractors more time and labor to install. The course I took suggested that the crew time to install the first Euro window should be planned for 8 hours and then that timing will slowly reduce as they install more.

 

[Max W]

With the suggestion of the "Not so big house" book, I'll also throw in a suggestion for the newly published "Pretty good house" book by several authors. Provides a good list of things to think through when designing a home..... Basically with the aim of building a house better than code, but not necessarily passive-house levels.....and making sure you stick $ where it makes sense. (No sense in paying for a double stud wall if the heat loss from your skylight or double pane windows outweighs it... maybe a single stud wall with triple pane windows makes more sense, etc)

I'll offer up this: Make sure you have intake air for the stove, or at least the ability to add it, and controlled air for the home.

Pretty Good House

The Pretty Good House approach to home building and renovating details a pathway to building better than code minimum which describes the worst house you can legally build. The info is vetted by leading experts in the field of fine homebuilding, high performance and green building and the profession

www.prettygoodhouse.org

Great site. Just checking out the youtube video there and got drawn into watching it all. Extremely doubtful there are any more house builds or rebuilds in our future and, even if possible not likely to this level. It is still interesting and exciting stuff.

 

[begreen]

"just a small heat pump, no furnace." <--- That's vague. I'd love to know what their cooling and heating loads look like in reality.
Kudos to them for not building a giant house, sounded like a reasonable size for their needs.

With winter heating bills that are just the basic connection fee, they are not using the heat pump a whole lot. This house is built with serious insulation. Enough so that human body warmth, lighting, and cooking are part of the thermal supply.



This is the builder's website:

Passive House — GO LOGIC

www.gologic.us

 

[Poindexter]

I have learned some more about windows. I will probably have to go with only a few on the north side, and they will be smaller than the ones on the south wall. Most likely. Dang it.

 

[Nate R]

With winter heating bills that are just the basic connection fee, they are not using the heat pump a whole lot. This house is built with serious insulation. Enough so that human body warmth, lighting, and cooking are part of the thermal supply.

View attachment 308688

This is the builder's website:

Passive House — GO LOGIC

www.gologic.us

Yeah, but the article says this:
"Relying a lot on the sun to heat, which in the winter is pretty amazing."

The sun streams in through a wall of windows on the south side of the home, and onto a rooftop solar array that McCunney says on bright days like this will generate four times as much energy as the house needs.

That means that the only heat or electricity bill they pay in the winter is the connection fee to Central Maine Power — about $13 a month.

I don't know what the net metering scheme is out there, but they could bank thousands of KWH in the summer for credit in the winter....So again, I'd love to know the actual heating and cooling loads. When they claim a Passivehaus is "only" 10% more expensive, and then leave out a lot of other metrics, I get skeptical.
-----------------
OK, dug into the builder's blog, and they have an entry about this home: Patrick: We have 27 360-Watt Q CELLS panels on the roof, so the system is about 9.7 kW. I installed a hybrid inverter for battery backup in the future, but right now we’re just selling our surplus power to the grid. Our energy usage has averaged 12 to 15 kilowatt-hours per day, up to 25 or 30 during the coldest part of the winter. But on a sunny spring day like today, we’re exporting about 60 kilowatt-hours per day, on average, so it’s completely net-positive

What's not clear to me is if that "25 or 30" KWH of use is from the grid (not looking at the panel contribution) or total use. If they're using an extra 18 KWH/day in winter for heating in the worst case, with a COP of what, 2?....Then we're in the neighborhood of 5K BTU/hour net heat loss. Fantastically low, yes. But still a bit murky...was that a 30kwh/day average over the coldest month?
To me, when there's discussion about improved efficiency, the up front cost of lower-carbon buildings, etc....I'd like to see more hard #s than just framing the idea. And maybe that's my bias towards Pretty Good House building.... looking harder at the tradeoffs and compromises. Is the financial input of those 15 inch walls worth it?
It's tough, I get this article was written for the masses, but I feel including some stats would be helpful to convey just how much better these types of houses are, especially when the idea is that "Hey, building houses more like this is worth it."

 

[PassionForFire&Water]

My plan is for similar windows on all four walls.

Once I have a lot and have chosen a site on it and know where the wind comes from and what the existing trees are, then I can think harder about windows, or translucent panels. Or even headered openings in the framing now for future windows or even passageways into an extension later.

I may need to blank out a couple of the windows for the home theater system screen on an exterior wall, but I would rather not.

I loathe, simply loathe, rooms in typical suburban homes with one small window on one wall, and three walls of surface on which to store stuff. Having windows on two walls in one room elevates the space, in my mind, from a simple cave in which to survive to a civilized space in which to think.

The potential for 360 degree views from the loft, save the bathroom at the top of the stairs, is thrilling to me.

The point about knee wall insulation is not lost. Having a great hat and a great coat out in the weather with no neck wrapping is a similar wardrobe malfunction.

View attachment 307800

You need a much smaller hammer!

 

[Nate R]

I have learned some more about windows. I will probably have to go with only a few on the north side, and they will be smaller than the ones on the south wall. Most likely. Dang it.

You say dang it, but again...tradeoffs!
I put a large window bank (9'wide x 6' tall) in my cabin that faces.....Northwest! And used only single low e coating windows there. I understood the heat loss from those windows would not be tiny, but I'm OK with that. Just like the skylight I put in... the rest of the roof is much better insulated, but the improvement in natural lighting, feel, etc is worth the energy loss to me.

There's a great article in GBA about how to actually calculate the net heat gain/loss of windows here: https://www.greenbuildingadvisor.com/article/a-quantitative-look-at-solar-heat-gain Not sure if it's behind their expensive paywall or not...

I see a lot in some places about "south facing windows for winter solar gain" etc....with it never quantified. This article shows the math involved, and it varies TREMENDOUSLY by location.

 

[begreen]

Yeah, but the article says this:
"Relying a lot on the sun to heat, which in the winter is pretty amazing."

The sun streams in through a wall of windows on the south side of the home, and onto a rooftop solar array that McCunney says on bright days like this will generate four times as much energy as the house needs.

That means that the only heat or electricity bill they pay in the winter is the connection fee to Central Maine Power — about $13 a month.

I don't know what the net metering scheme is out there, but they could bank thousands of KWH in the summer for credit in the winter....So again, I'd love to know the actual heating and cooling loads. When they claim a Passivehaus is "only" 10% more expensive, and then leave out a lot of other metrics, I get skeptical.
-----------------
OK, dug into the builder's blog, and they have an entry about this home: Patrick: We have 27 360-Watt Q CELLS panels on the roof, so the system is about 9.7 kW. I installed a hybrid inverter for battery backup in the future, but right now we’re just selling our surplus power to the grid. Our energy usage has averaged 12 to 15 kilowatt-hours per day, up to 25 or 30 during the coldest part of the winter. But on a sunny spring day like today, we’re exporting about 60 kilowatt-hours per day, on average, so it’s completely net-positive

What's not clear to me is if that "25 or 30" KWH of use is from the grid (not looking at the panel contribution) or total use. If they're using an extra 18 KWH/day in winter for heating in the worst case, with a COP of what, 2?....Then we're in the neighborhood of 5K BTU/hour net heat loss. Fantastically low, yes. But still a bit murky...was that a 30kwh/day average over the coldest month?
To me, when there's discussion about improved efficiency, the up front cost of lower-carbon buildings, etc....I'd like to see more hard #s than just framing the idea. And maybe that's my bias towards Pretty Good House building.... looking harder at the tradeoffs and compromises. Is the financial input of those 15 inch walls worth it?
It's tough, I get this article was written for the masses, but I feel including some stats would be helpful to convey just how much better these types of houses are, especially when the idea is that "Hey, building houses more like this is worth it."

Send a letter or call the builder for specifics. I'm interested too, though my house-building days are probably over. I'd also like to know more about the triple-pane German windows used too.

 

[peakbagger]

Here is good detailed course on high efficiency windows and coatings for free https://www.heatspring.com/courses/all-about-windows

I havent done solar heat gain calcs through windows for decades. In the old days we looked up net gain and net losss values from tables for latitude and time of day and then set up big spreadsheet. As the early passive solar folks learned it was real easy to over heat a space even on a sunny day in the winter but the windows were still a major net energy loss for the 16 hours of day where it was dark. My double cellular blinds are supposed to double the effective R value of the window opening but on cold night my thermal camera can see a dark spot in the wall. BTW, usually there is thermal mass incorporated in the interior where the sun hits in the winter, it soaks up the heat during the day and releases it in the evening. Generally at high latitudes, the windows may need to be equipped with either active or passive shading to keep out the summer sun.

With respect to Passive construction, the builder is just chucking the law of diminishing returns and trying to approach zero. My guess is when doing heating calculations even with super efficient euro windows, the windows are still major energy hogs. At some point I will be modeling my new house design and it will be interesting to run the economics.

It is interesting that they have adopted the European insulated slab system in place of conventional foundation. Frost depth in Maine can vary but in coastal Maine its a minimum of 4' going up to 6' in Northern Maine. The soils can have shallow water table and bulding a conventional foundation and keeping it dry is quite expensive. Most do no use that space for living space for code and aesthetic reasons so they are saving some of the cost of deep foundation by going with insulated slab. That can work except that all the exposed foam is bad news as carpenter ants love to tunnel and nest in foam. A far as I am others are concerned that is fatal flaw for the pictured cross section. To date I have not heard of any foam products that are resistant and once they get in there it will be very difficult to get them out and they inevitably will find a way into the house. The pictured wood fiber insulation is interesting. To date there are no domestic manufacturers of that product and it would need to be shipped in from Europe at high cost. There is a plant going on line this year in Maine with a annouced date for production of the board material late this year so maybe the builder is an optimist. It is impregnated with borate so no ant issues and the claim is its vapor permenable.

I am unsure why they went with such a deep interior wall. There is no structural need and my guess is they are doing it for R value but why not go thinner on the interior and thicker on the wood fiber exterior? No matter what its thick and will make the window trimming pretty interesting.

 

[DBoon]

My guess is when doing heating calculations even with super efficient euro windows, the windows are still major energy hogs.

Yes, absolutely. I did extensive detailed heat loss calculations for my home (which have proven to be very accurate now that I am living in the home) and (working from memory), the windows were about half of the total heat loss of the house (18,000 BTUs at 0 degrees F), I saved most of the old wood windows (using wooden storm windows, gasketed bottom sash, bronze weatherstripped on the sides) because it would be just a waste to get rid of perfectly good windows, but if I had replaced these R-2 windows with R-5 "better" windows, my heat loss would only have gone down about 4000 BTUs/hour (again from memory).

Some windows had to be replaced due to renovation or bedroom egress requirements. But I didn't replace them because the heat loss would be dramatically reduced.