Category Archives: heating with wood

Go small or go home?

Here’s how I see it…. if you are building/renovating a house and you are trying to:

a) build net-zero (primary energy) instead of the typical approach (climate-independent) of keeping utility bills to less than a few thousand dollars (meaning less insulation in warmer climates)


b) not trying to go (too) broke


c) you have good sun

then you have a few options:

1. passivhaus with PV
2. more typical superinsulated with PV
3. passive solar with woodstove and PV
4. active solar (perhaps not with even a woodstove) and PV. Done right, I suspect this active solar can be done on the cheap — the Yahoo Groups SolarHeat and SimplySolar and Gary’s website have some smart people with some ideas. (One needs to be able to get through 5 days of clouds to have 97.5% solar fraction)

In the first two cases, there is some advantage to building a small house. In the latter two, less so, because if the solar thermal (heating & hot water) is sized appropriately, then who cares how big the house is! The sun is free!

From what I can tell so far (our 1-year experience), here are the problems with small/ish houses:
1. It might mean you are building/buying something a little weird or not typical. So if you are unsure how long you will be there, resale could be an issue untill we get to the point that people are generally drooling over superinsulated homes.
2. If you have little kids (and especially if you are in a cold climate and/or don’t live in cohousing with a big shared common house) you might go a little bonkers if you don’t have room to let them run around in circles.
3. Stuff. Junk. Accumulation. (And see #2 if you buy your kids too many useless toys)
4. A smaller sun-facing wall/roof means less room for solar panels.

So, if you are going to build small and have kids, there is some advantage (I think) to building on as few stories as possible. Ignore the “a cube has the least surface area” business. It’s not worth worrying about (too much) if you have kids. Don’t waste room with hallways. But try somehow to have a loop! Keep lots of rooms. Just make them smaller. Don’t be afraid to use point-source heating. We wimped out a bit and have 4-heads to our minisplit system (one per floor). But it would have worked fine with just 2 certainly. I still like a basement. Nice way to get the mechanicals out of above ground places with views. And room for a solar heated water tank.

That’s the view from here.

Do you have kids and live in a small/superinsulated house? Let me know how it’s going? Right now we have 8 people (4 kids under 6, 4 adults) living in what PHPP calls 1741 sqft TFA (treated floor area). And it’s fine. Beat that! Actually, I bet you could. As we built “up”. Do as I say, not as I do! 😉

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Experimenting and sharing the results

“I built a [solar thermal heating] system that I subsequently figured out didn’t make the most sense – why can’t others discuss the shortcomings of their experiments? People must like story-telling more than science.”
— Mark Sevier, PE (our “neighbor”)

From article:
Using Sand to Store Solar Energy
Assessing the controversial claim that solar thermal heat gathered in summer can be stored in sand for winter use

Go Mark! I think also, people are busy, and so after they have built a house, and perhaps it doesn’t work as well as hoped for — in terms of being 100% solar, or zero-energy, or meeting the passivhaus standard (or pick your criteria) — then people are loath to brag/blog about that. But I think it’s certainly useful and will help others learn from our experiments and/or mistakes.

Our house is *pretty much* working as expected I think, but I don’t think quite as well as the PHPP perhaps estimates, and certainly there are lots of things I would advise people to do differently, but that’s ok! (*”Pretty much” as in… our heating bills are VERY VERY low — like maybe 1/5th or a 1/10th of typical house of this size?) We are on target to use approximately 10,000Kwh total for all purposes for the year (june2010 thru may2011) I think. That’s heating, hot water, electricity, lawn mowing, etc). But that’s minus car use, buying stuff, food, etc. We could be living much greener! We’re working on it!

See also:
Mark’s House — a 14 HERS house in Sudbury, MA
Other comments from Mark at GBA — favorite Solar Homes section
Solar heated buildings of North America: 120 outstanding examples by William A. Shurcliff
Edision: The experimenter’s journal

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Net zero in New England seems easy now…

Net zero in new england seems easy to me now… and here’s a little about why…

First some qualifications:
– I am talking about new construction since that is what I am familiar with.
– By easy I mean “not that expensive” by which I mean, it is doable for the same (net cash flow) as a typical new house.

The reason it seems easy is because we seem pretty close to on target to be net zero for the year, and we don’t even have:
– solar hot water heating
– and more importantly… solar air heating
– the house isn’t all that small. I mean, it’s smaller than a typical new house with 4 people living in it, but in retrospect, I think a different design might have been more efficient. I will talk more about that in the future.*

Solar Air Heating
What I realize now, more than ever, is that it is not difficult or expensive to design an inexpensive solar air heater for a house that gives 100% of your heating on a sunny day, even if it is 0F outside. That’s because you don’t need all that much (even in New England) if you have insulated enough. The method that I am most interested in at the moment is Aluminum Downspout Hot Air Solar Collector–which is quite unobtrusive… (youtube) Read more here at

You want in?
1. calculate how large a collector one would need, you need to first estimate your house’s “heat load” using PHPP (if you are building a new Passive House) or get a pretty good estimate using this form or the excel file here as an example.
2. build it! With your kids!

Here’s what I would do if I were to do it again:
– double stud walls 12″ with dense packed cellulose by an installer who knows what they are doing and has the right equipment
– air barrier at the exterior — taped Zip system walls perhaps. Meaning… applied eaves. Search on Marc Rosenbaum applied eaves, etc.
– ventilated/cold roof with insulation on attic floor, no ceiling cans on 2nd floor, etc. and a hatch on exterior of the house to access this space if need be.
– Don’t worry about the roof angle being 45 degrees (near your latitude) or being exactly solar south. Maybe even a shed roof so there is even MORE roof for solar panels.
– heat with a wood stove or pellet stove, looking to Rachel Wagner for any advice on best practices for heating with wood in a tight house
– Use an HRV
– I like having a basement to put mechanicals in, but if I were to do it again, I would probably build only 2 bigger above ground floors and keep the attic level outside the envelope. For a number of reasons. I will write more on this in the future.

Basically, I would follow the rules of building a superinsulated house, even Passive House, but not go too crazy with expensive closed-cell** spray foam insulation or very expensive windows. Pretty much what we did, but I would try to spend even less, and if anything, spend the difference on solar heating!

What’s my point?
The point is… even in a superinsulated house, heating is a big part of the overall energy use (if looking at heating, cooling, hot-water heating, cooking, lighting and appliance use in a household that is reasonably considerate of their usage.) So if you can cut this, even by 25% due to solar, you are going to be in much better shape. Some will argue that is better to spend solar dollars on PVs that can be used year-round, but in cold climates with very efficient solar-thermal heating done on the cheap with the help of and “simplysolar” and “solarheat” yahoo group participants, the cost per KWh of energy saved is going to be much lower.

*A neat book on small houses is Little House on a Small Planet: Simple Homes, Cozy Retreats, and Energy Efficient Possibilities

**Some closed-cell foam is still going to be useful in certain spots — like the rim joists. Just be sure to use a brand with water as the blowing agent so you aren’t adding to the greenhouse effect due to HFC-134a. (article discussing foam insulation and GWP)

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Devil’s Advocate: Air-source mini-split heat pumps

First of all, we heat our house with air-to-air mini-splits, so I am just playing devil’s advocate, which I love to do. We know the pros of air-source heat pumps right? (consistent electricity prices, often green options for electricity, including onsite PVs, low installation cost, AC “for free”, etc) But let’s hear some potential cons:

1. Fan running all the time on outside compressor (it’s just like an AC compressor… the fan runs hardest when it’s coldest trying to eke out something minimal like 1.2 COP) . Ours happens to be slightly mis-balanced for some reason and they haven’t been able to fix it yet so guess what, it’s NOISY outside when it’s 0F outside. How annoying is that? (Edit: I think we are just unlucky and that air-source heat pumps are almost always pretty much silent. That’s what the specs seem to say… I’m sure ours will get fixed and I’ll post an update here!)

2. Defrost coil. I forget what it’s called exactly (need to refer to the service manual), but our Mitsubishi model has something running all the time (there is a dip switch) which I believe is preventing freeze up when the system happens to be off in the cold. And it’s 50W-100W (I’m not exactly sure… I will report back). So add that up for 7 months. Heating the outdoors as they say. Assuming 50W * 24hr * 30 days * 7 months = 252KWh. That’s what we use for an ENTIRE month in the summer. Ouch. (I’ll update here when I have final measured numbers. SEE ** below)

3. Snow happens. We’ve had a VERY snowy January and 3 feet of snow on the ground. This means I have had to do a little shoveling around the outside compressor (which sits maybe 8 inches off the ground — pad plus little legs) to keep the air flow free for the fan. The fan does a very good job of this itself (causing a huge drift in front of it — photo coming) but it still seems like a good idea to do a little preventive shoveling right around the unit where a little snow piles up. In other words, it is not totally “set it and forget it” like a typical furnace or boiler might be (assuming you don’t forget to schedule a propane or oil delivery!) That said, one needs to make sure the exhaust vents for a fossil fuel system in your house are clear, so I’m not the only one checking/clearing snow. I believe there are new building regs in MA which require vents to be 8 feet off the ground.

4. No central control with multiple heads (for us). I think there are some more expensive models which can control multiple interior heads with one controller (like from Daikin) but ours is not like this. Not a big deal, and it can be seen as a plus, like radiators which typically have a few zones with individual thermostats. Just sayin… it’s not like “forced hot air” systems which are normally just one big zone. Unless you have a very small house and/or mild climate and/or passivhaus-esque envelope and use only a single head.

5. Slow to pick up the slack. It’s maybe silly (I think there are articles out there showing that for a super-efficient house like ours, setbacks don’t end up mattering much at all), but I can’t bring myself to keep the temp pegged at 68F at night. So we do set back the temps a bit. It’s been my impression that in the AM one needs to set the temp very high (like in the 70s) to get the room temp up to snuff relatively quickly, especially if it’s very cold outside and the output of the unit is low. And that’s annoying cause then you need to remember to set it back to 68F again. (The flip side of this is no temp swings… with a heat pump, it is always running (quietly) and so the temp remains constant. Vs our last house with forced-hot air which would crank heat LOUD then turn off then ON again and repeat.)

6. Stuff breaks. And when it does, it doesn’t seem like things are not necessarily in stock and ready to repair THAT DAY like it maybe is for a oil-fired boiler. (Feedback?) It’s been my experience that it means a special order from a regional supplier or sometimes the US distributor and both take time. Now, maybe there is evidence that these things break less-frequently, but… just sayin. I don’t think this is going to happen with a wood stove, is it?

7. Speaking of wood stoves…. even if you are operating with a good COP (of say 3 on a mild day) it is still using electricity, as opposed to solar or wood, which I think are better for the planet!

8. Source Energy…. And speaking of COPs (coefficients of performance) if you live in a cold area, even with the new fancy Mitsubishi and Daikin or Fujitsu models which operate pretty well at 0F and -5F, you are still talking a COP of only 1.5 I believe. (And has anyone verified these numbers? I don’t have reason to doubt, but how would one measure?) Anyway, the problem with a 1.5 COP is that if you assume (in the northeast US) that a high percentage of your electricity is coming from a power-plant using fossil fuels, the problem is that power plant has to burn 3 KWh of fuel to get 1KWh of electricity to your house!

So here’s the math on source energy:
3KWh burned at the plant => 1Kwh delivered to your house * 1.5 COP of heat pump => 1.5 KWh of heat delivered. (50% efficiency, source to site!)

The seasonal numbers reported (in the form of HSPF) is usually like 2.5 COP (if I recall correctly… I use the Canadian scores, which I believe adjust downward, dividing by 1.15 vs the US numbers for whatever zone North Carolina is in I believe). So 2.5 / 3 = 83.3% source to site efficiency averaged over a year maybe?

So… it would have been a LOT better to burn some natural gas or propane right at your house at 90% efficiency. You’d be 90% source to site efficiency!

Or wood! Or sun!

9. Vacation set backs. Unless I am missing something, the lowest the heat settings go on our mitsubishi system goes is 59F. What?!!!!! I would set back my house temp to 45F if I were away if I could! Maybe (I can figure out a way to fool it, like one can with a typical thermostat with those 15F setback timers you can control via X10.) What a hassle though!

10. Oversizing for design temps. I think the 90-something design temp is 6F for our area. And according to manuals, our system is only operating at roughly 30% of rated capacity at that temp. So either you have to oversize, or use some back up heaters — electric radiators seem to be what I hear people use. Or wee have a few small plug-in heaters.

11. Wet clothes after playing in the snow. How do you get them dry? In a typical northern house, I would put them on a radiator or forced-hot-air vent, in the boiler room, in front of the wood stove, etc.
Those don’t exist in this house! And we axed the clothes dryer too! I guess this is where one of those bathroom towel-dryers comes in handy. Or we use a typical dehumidifier in our big mudroom closet. Works ok. But still, just sayin! You can get floor models for air-source heat pumps I guess. Maybe that would do the trick. But that takes up more space.

12. Anything I’m missing? Let me know!

Heating with Oil or Gas: What’s to Like?
We may not like it, but heating with oil or gas is really convenient.

Is Radiant Floor Heat Really the Best Option?


** (from our MXZ-4B36NA service manual PDF)

If moisture gets into the refrigerant cycle, or when refrigerant is liquefied and collected in the compressor, it may interfere
the start-up of the compressor.
To improve start-up condition, the compressor is energized even while it is not operating.
This is to generate heat at the winding.
The compressor uses about 50 W when pre-heat control is turned ON.
Pre-heat control is ON at initial setting.

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VS: home heating — heat pumps vs wood (or solar)

There are many in green circles — superinsulated/zero energy home/passivhaus circles — who think that heating with electricity (ideally with an air-source heat pump) is the ideal way to heat a house with solar electric (PV) panels on the roof (well, or yard). Example link

As someone with a house that is exactly that, let me chime in.

Heat pumps: PROS
1. No hole needed in house for exhaust or air intake
2. No air-quality or safety concerns since no burning of wood or fossil fuels in the house
3. Math is easy if you are trying to be net-zero. If everything is electricity, then there is no complicated math to do converting gallons of propane or cords of wood burned into KWh. (not much of a reason)
4. Now you have AC too. OK, so you saved a few bucks. Window ACs are only $80 though. And you house probably doesn’t need much more than one of those. Really.
5. No baseboards taking up space. But there are other approaches (forced hot air and such) to deal with that.
6. Quiet inside. Wow, very very very quiet. No furnace, furnace fan, or boiler making a racket. (Aside: And no humidifiers in winter… thanks to the tight superinsulated house part…)
7. Electricity tends to be price-stable vs the price of propane and heating oil which seems to whip-around a lot.
8. Usually a bit cheaper to install vs a “central” system esp in a very small house. But add in the price of the HRV or ERV stuff if you have that too.
9. Point source: I list “point source” below as a con too. Some like point source heat since it allows zoning, getting cozy by the “fire” and such. Flip side to everything.
10. Future safe. Electricity can come from many primary sources.

Heat pumps: CONS:
1. Can be a bit loud outside (well not LOUD, but there is a fan running, like for central air-conditioning, all winter) So if you are noise sensitive maybe there is a quieter heating approach? Not sure what qualifies as the quietest. Radiant floor heat?
2. PVs should not be thought of as anything more than an offset in my opinion. Don’t think of that electricity your panels made as yours. Who cares WHO uses it. The point is to reduce CO2/greenhouse gases overall. In other words, if you make electricity, dump it into the grid for your neighbor to use, and burn some wood to keep warm instead, then you are ahead (in my eyes) of someone using that electricity directly to heat their house with a heat pump.
3. In very cold areas, you will need either a HYPERHEAT model that keeps up with sub-0F temps, or some back up (maybe electric space heaters). Most other air-source heat pumps drop their output by a lot when it is VERY cold.
4. Power outages. You will have no heat. Now, that might not matter as much, because your superinsulated house has a certain amount of “passive survivability” built into it with all that insulation, but if we are talking comfort here, then grab a wood stove or a propane heater needing no electricity to run. There are a few!
5. “Non-traditional” Looks: Some might think they are ugly. I don’t mind them. Just different. And controls. Our Mr Slim one has a “remote” vs a traditional thermostat. And the model we got doesn’t control all 4 internal heads. So like a house with zoning, you have to walk around and set each individually.
6. Point source: We have 4 of these inside “heads”. One on a wall on each floor (basement, 1st, 2nd, 3rd (attic)) But there is not heat/coolth pumping into every last room. Doesn’t matter much, but bedrooms are a little cooler — 5F? Coldham/Rocky Hill study seems to say. Ask google.

Wood: PROS
1. Local
2. Carbon neutral
3. Ambience
4. Simple technology (especially if not pellets and not catalytic)
5. No electricity needed (heat when power outages)

Wood Stoves: CONS
1. Lugging stuff
2. Might be difficult to vent properly in a very tight house. Indoor Air Quality risk. Especially with a pellet stove which loses electricity.
3. Even the smallest pellet stoves will overheat some houses that are superinsulated. But big whoop. Run it on thermostat-mode. And open the window if you must!
4. Particulate pollution. You might live pretty near other people or in a town or city that prohibits wood burning.
5. Related… Gotta know what you are doing. (slow-burning, smoldering wood stove fires pollute like crazy and smell up the neighborhood.)

Solar Thermal Heating: MIGHT BEAT WOOD IF…
1. You have sun
2. You have a spot to put the solar thermal panels and a HUGE 1000 gallon tank in your basement
3. You have already done energy efficiency fixes — insulation, CFLs, etc. (see
4. CON: Up front cost is going to be higher than the wood (at least a pellet stove vented out the side of a house) unless you are a DIY person (see

Prius: PROS (W/holistically speaking, maybe this is a better place to start…)
1. Do the calculations in KWh. If you cut the number of gallons of gas you use in half by driving a hybrid or electric car, how much is that in KWh?
2. Energy Independence: coal and nukes (for making electricity) are “local” to the US, vs gasoline comes mostly from other countries. Propane is 90% from US. Natural Gas is ???
3. Use as a backup generator for house

So what would I do?
Well right now we use an air-source heat pump to heat our almost passivhaus ZEH. But I hope to do more solar-thermal heating in the future. 5 days of storage would get you to 97% solar “if cloudy days are like coin flips”. And the no-electricity propane heater is intriguing, especially for a little backup. Check back in a year!

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VS: electricity vs propane — New England style

1 gallon of propane is $2.80 right now on avg in the US says the web.

If you assume 90% efficient boiler or furnace, that is how many KWh of heat delivered to the house?

1 gallon of propane has ~91500 BTU = 26.82 KWh * 90% efficient = 24.13 KWh delivered for $2.80


So how much does that amount of heat cost with an air-source heat pump if you pay $0.15/KWh and assume a COP of 2? (being very conservative… our seasonal avg COP is supposedly 2.7 I think I estimated once using Canadian (cold) figures from service manuals)

24.13 KWh / 2 COP = 12.065 KWh * $0.15/KWh = $1.81

Even if you are heating with straight resistance electricity (no heat pump trickery), the cost is only $3.62 (vs $2.80 for propane). Not bad, $-wise.

1. The propane would be much greener since electricity from power plants is very dirty in the northeast. IOW, the carbon/KWh heat delivered is 3 times higher due to inefficient power plants using fossil fuels. Better to use the fossil fuel directly.
2. If you are in a warmer climate, the math for the heat pump is even better, since you COP will be 3+.
3. If you can use zoning (heating one room) with an electric heater, you will probably be ahead (in both $ and green) vs central-heat using propane.
4. Wood heat or solar beat everything.

Next week: electricity vs heating oil

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No furnace: it’s true

It’s true that our super-insulated house, almost a passive house, has no furnace, but does that matter? To many people it is a significant point having no central furnace or boiler in Massachusetts/New England. But have you ever rented an apartment with electric baseboard heat? (No furnace) Have you ever heated a house just with wood? (No furnace). See what I mean?

What the headline should be is NO FURNACE AND STILL COMFORTABLE AND INEXPENSIVE TO HEAT WHEN IT’S 20F OUTSIDE. Or something like that.

Because the real story is there is a lot of insulation which makes it possible to heat (or cool) the house very comfortably without a lot of energy.

Who else has no furnace? Well, it’s typical of passive houses. Like this one in MN (our electricity bills are similar). But it’s also true of other well insulated homes. Like these and these and this one. But they still have heaters. Just point source. Rinnai direct-vent heaters, air-source heat pumps, maybe a tiny bit of electric baseboard.

And it’s true of some solar houses. Like this one or this one. More at

And also true of people who are experimenting with zoning using electric space heaters. (But a reminder… if your electricity is coming from a fossil fuel electricity plant, it’s probably not a good trade.)

Some advantages of our house with no furnance:
– It’s QUIET!
– Not much to break, and if it does, or if the power goes out, the house has so much insulation, and mass (dense packed cellulose) and is so tight, that it stays warm longer than a typical house

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Visualize Energy

One thing I find useful when thinking about being frugal on energy use (and maybe I’ve written about this before) is attempting to visual the energy involved. Trying to make the invisible more real, more concrete.

So for instance…

– That’s one side-benefit of heating with wood or wood pellets. You can SEE the stack of wood. You can FEEL the stack of wood (when you carry in the bag of pellets, split the logs, etc.) We partially heated our last house with 3 tons of pellets each year (1 pallet = 50 x 40-lb bags = 1 ton). Partially heated. Carrying 3 tons around makes a person think.

– When I think about driving somewhere, I do a quick mental check… OK, so that’s 50miles roundtrip, so that’s ~2 gallons of gas in our 26-27MPG average car. Need help visualizing a gallon of gas? Think a gallon of milk.

– I can do the same with comparing the relative merits of turning something off (negawatts) vs the offset of the PVs in 2 ways: 1) considering the 24KWh per day output of our entire PV electric solar array. “How many days is that?” Or alternatively 2) “How many panels worth is that in yearly output?” (Each panel outputs 300 KWh a year)

– This reminds me of the visualizing energy that one can do when trying to lose weight by exercising. OK, so if I run for 40 minutes, that’s X calories, and if I eat that bowl of ice cream that Y calories, etc. Except for your car or house.

That electricity grid, oil tank, propane tank, etc. is pretty darn convenient, but by it’s nature of being hidden and automatic, keeps me from thinking too deeply about my energy use. Wood and solar have a nice way of getting that a bit more into the open.

A flow meter on the water line going into the hot water heater, and devices for monitoring electricity use, like the TED5000, Kill-A-Watt, eMonitor, etc. can help with this too.

Google Powermeter is an interesting project too. If one could compare one’s own energy use to your neighbor easily, that would be informative.


visualising energy consumption by Jorn Barger at Robot Wisdom blog


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on self sufficiency in the 21st century

“Part of the point of being self-sufficient is to get away from the experts.  Look at the mass of people in cities: they live in houses designed by experts, they go to work in vehicles made by experts along roads laid out by experts, they make things designed by experts and sold by experts, they eat a meal produced by experts and they are entertained by yet more experts.  All they do for themselves is sleep.”

Andrew Singer, in “Methane, Fuel of the Future” (1973) as quoted on pg 300 “Solar Energy” (1976) by Daniel Behrman

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