Category Archives: HVAC

Concealed duct indoor units for air-source mini-splits**

idea 1) Add a single zone minisplit that directly feeds 3 rooms with only 1-zone via tiny duct runs. Mitsubishi and Fujitsu both have these. I think the indoor unit might fit in the ceiling of a closet and losing 8 inches might be acceptable? The idea being that we could then turn off the “central heat” completely on cold nights and during the day. $2000?

idea 2) Much cheaper — thicker down comforters, sweaters, fleece, hat, my 100W electric panel under-desk (vs 1500W space heaters) with blanket for a sort of “homemade Kotatsu”. The problem is that fingers still get cold and it’s more flexible and more comfortable to not bundle.

idea 3) Some combo of the above.

idea 4) pellet stove or wood stove. Problem being that it would be mainly heating the big common space so getting heat to the office/bedrooms would be tricky.


**Main goals are: 1) save $ and 2) KISS (Keep it simple, stupid) and 3) reduce carbon

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If you are pondering indoor air-quality…

If you are pondering indoor air-quality in your home… I urge you to look into the issue of flame-retardants in furniture — specifically in the foam used in mattresses and couches.

Here is an upsetting recent article on the topic PBDEs and chlorinated Tris (I knew about PBDEs, but hadn’t considered that (DUH!) the replacement would probably be just as bad or worse. And that they don’t even work!)

Some good practical advice here (if you are a millionaire)

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2011/12: The year in heating

We have an emonitor gizmo that tracks our home energy use by circuit. One circuit is the air-source minisplit heat pump (the heat and cool in the house).

For the YEAR ending April 2012, the heatpump circuit shows:

3,009 KWh (total for year, heating and cooling and some hot water)
2,598 KWh (Oct-Apr — 7 mostly heating months)

Remember that we also heat our water with an air-to-water heat pump in the conditioned basement, so during the heating months, it is stealing heat from the house. So the 2598 includes some of that. Let’s pretend it is 10% of our total load (no idea) so that would be

2338 KWh (Oct-Apr — mostly heating months. HOME HEATING ONLY)

If we pretend the price we pay for electricity is $0.15/KWh (it’s more complicated than just a simple number like that with this and that charges) but close… then that is:

$350.70 (our estimated heating bill for winter 2011/2012)


(Well, and actually… minus some significant fraction of that which is covered by our PVs (electric solar panels). We don’t have net metering, so our electric bill is rarely $0 even in the summer. I just don’t unclude the PVs cause I generally think of them as an offset. Not an important part of the house.)

– The silly 20KWh/month our minisplit uses whether it is on or not. Nothing to do about that at least in the winter. But I could flip the dip-switch for 5 months of the year.
– Someday I will add a submeter for the minisplits since the emonitor is probably 10% off in some direction. (I believe that’s the spec I’ve seen.)
– More PVs, perhaps this string with a central inverter and small battery for:     – night-time (since no net metering) and
    – power outages (we have a well so it would at LEAST be nice to have running water when the power goes out.)

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We’d be net zero but…

Our house would be net zero source energy but…

- well filters: we avg 54 KWh / month
– well pump: 10 Kwh / month
– radon fan: 40 KWh / month
– 2 home offices: 60 KWh / month
– Mitsubishi minisplit: 20 Kwh / month (EVEN WHEN OFF DUE TO A COIL HEATER THINGY!)
– electric lawn mower: (not much, but just sayin’)

What else did I forget?

So that’s 54+10+40+60+20 = 184 KWh / month
= 2208 / KWh per year

… that we can’t help that some other net-zero types of house don’t have since our house has a well and 2 home offices and a mitsubishi mr slim air-source heat pump with what I would consider a design flaw!

We use approximately 10,000 KWh per year for everything (heat, hot water, lighting, cooking, etc.) And our 6.9 KW PV panels make about 8,400 KWh so if we didn’t have the extra 2200 KWh, we’d be easily net zero.

BUT… then there is driving. Someone who lives in a city in and walks everywhere is blowing us away. We drive maybe 15000 miles per year at 20 MPG (minivan). There goes net-zero.

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Summer with a WORKING hrv – latent vs sensible loads

Last summer our HRV was mostly busted/confused. It was confused by controller wiring and was running in recirc mode where no fresh-air is pulled in. I figured it out using this CO2 meter after being annoyed that CO2 levels (monitored by a Telaire 7001) were not dropping in the house, even when the HRV was running on high/5.

Anyway, the point is, it will be interesting to see if we need to do something like the link below describes this summer. Namely using our standalone dehumidifier to dry the house off since we will probably not often actually need much AC (when it was 100F last summer, we would turn it on just a little at around 5pm). Or maybe the hot-water heat pump will dehumidify things enough even with the HRV bringing in some moist outside air (it’s pretty ridiculously humid at times in the summer here in MA).

Actually, I think the minisplits have a dehumidify mode, but I bet there is a catch.

LINK (see the section “Reduced Heat Gain” and the photo “Photograph 6: Hotel Room Fix”)

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Some HRV advice

Here is some quick HRV/ERV advice based on our experience so far:

- Do ASHRAE 62.2 stuff so you get the right flows to right rooms and size the unit appropriately. We run ours on setting 3 of 5, but maybe it would be preferrable to have the slightly larger unit running on 2. Quieter?
– Have duct routes planned out. Don’t leave it to the HVAC contractor to wing
– Keep duct runs short. use Ys not Ts, etc. Generally follow advice from the David Hansen article in JLC LINK
– Ideally get a contractor who has done HRVs before because it seems to me that not everyone is very experienced in balancing using pitot tubes, adjusting registers, taping calerfully, etc, etc, etc, etc. Basically it would be nice for someone who is good at measuring/verifying the installation. In our case, I’ve been left to do most of that.
– Choose a model that has good CFM per watt. Our Lifebreath 155ECM is good on that front, but there are some with even better “efficiency” in terms of heat recovery apparently?
– It’s no joke: having flexible ducting for the first foot or so is KEY in keeping the system quiet. It’s really amazing (ours didn’t at first).

Other random notes:
– We have the typical — exhaust bathrooms, fresh air to bedrooms — setup and find that it works pretty well in the bathrooms, but I’m not convinced it can handle when it’s like a sauna in there all that well. I will have to do some RH measurements. Occasionally we open a window. Once (on a winter day) a window was left 1/4 open and wasn’t noticed for 1/2 a day(?) because the house is so tight that it doesn’t cause much of a draft . Which really means another windows should have been opened if someone wanted to dry it out quickly.
– When it’s like 0F out, our system goes into defrost mode pretty regularly (I will have to check how often) which only affects you in that the fan speed is set to 5, so it will be louder off and on, on very cold winter nights. Maybe some units are better about needing this less? Who knows.
– I’ve also experimented with using a portable… DEHUMIDIFIER… same effect (the air is dried out) but you get to keep the heat you make! If you have space, this is a nice way to go in heating season.
– Consider exhaust-only ventilation with a whispergreen fan and make-up-air hole. There is discussion on about which is “better”. You got me! LINK

– I am going to add some “solar preheating” of the intake air. But according to the PHPP, this would not be enough in our cold new england climate to be able to heat the house. That’s fine.

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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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