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Community and Q&A

Off-grid small home ventilation

rockies63 | Posted in Energy Efficiency and Durability on

In a question posted on this site entitled “Ventilation for a Very Small Home” the author asks which system or product he should consider to guarantee a steady supply of fresh air for his 720 sq’ home. Several people suggested either an HRV or an ERV, with more people leaning towards the ERV. However, I don’t think the author mentions whether his house is grid-tied or not so while all of the suggested options may be viable for a grid-tied house I was wondering which system could be installed in an off grid home of the same size built in the Canadian Rockies? I know that 18 – 30 watts may not seem like much to someone grid-tied but it could add up to a substantial drain on the batteries in an off-grid house (especially if the ventilation system is running 24/7).

Some of the HRV and ERV models suggested in the other post were:

1. Venmar AVS E10 (HRV)

– Uses 54 watts on low speed (1.2 cfm/w)

– Runs continuously?


2. Venmar AVS E15 ECM (ERV)

– Uses 30 watts on low speed (2.2 cfm/w)

– Runs continuously?

3. Panasonic Intelli-Balance 100 ERV (FV-10VEC1) Cold Climate

– 50 -100 cfm

– At -22 degrees F the unit stops for 47 minutes, goes into a heat exchange mode for 4 minutes, then operates in the   circulation mode for 9 minutes in order to defrost. Maximum power usage is 84 watts for heating mode at -25 degrees outside temperature.

– Does it draw power only when in heat exchange mode and circulation mode?

4. Panasonic WhisperComfort Spot ERV

– Can perform optimally from April thru Nov in climate zone C (northern states into southern Canada)

– Set at 20 cfm for house under 800 sq’

– Below -20 degrees F the mechanical damper on the supply air will remain closed for one hour, open for 10 minutes at “low” mode

– Power consumption is 21 watts at 20 cfm

– Does it draw power only when in circulation mode?

5. Lunos Fans

– 18 watts

– Runs continuously?

If one of these small HRV or ERV’s is suitable for an off grid house should I pipe the bathroom fan’s exhaust through the unit or would ducting the bath fan straight to the exterior be better? Also, I plan on having a separate Broan range hood ducted separately to the exterior and was considering installing the Broan MD6T Make-up Air Damper just to balance out the range hood. Would the make-up air device still be needed if I used an HRV or ERV?

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  1. canada_deck | | #1

    Have you done the math to show many CFM you need for you space?

  2. GBA Editor
    Martin Holladay | | #2

    I've lived in an off-grid home for 43 years, and have many friends who live in off-grid homes. None of us has a mechanical ventilation system. If we need ventilation, we crack a window.

    During the winter, we get very few hours of sunshine. Making homemade electricity during the winter requires the operation of a gasoline-powered generator, which is noisy and expensive. We've all concluded that it's easier to crack a window than produce the electricity for a 24-hour-a-day fan.

    For more information on this issue, see "How to Design an Off-Grid House."

  3. Jon_R | | #3

    I expect that on a perfectly calm day, a cracked window under-ventilates and if the wind picks up, over-ventilates. Of course one can guess at the ventilation rate and manually adjust, but it would be interesting if someone produced an automatic passive vent that maintained a just-right rate.

  4. rockies63 | | #4

    Well, according to this article the formula for calculating the ventilation rate is:

    (o.o1 cfm/square foot of conditioned floor area) + (7.5 cfm/person) so an 800 sq' cabin with 2 people should require 23 cfm.

    Unfortunately, building codes in BC Canada require all new construction to have a ventilation system.

    So it would seem that I must install some kind of a powered ventilation system.

    1. Expert Member
      MALCOLM TAYLOR | | #6


      The introductory section of the new BC code ventilation requirements says they apply to all residential buildings "supplied with electrical power".

      To me that can be read as excluding off-grid houses. I'd seek clarity with an inspector to see if the section does exempt those with PV panels, or just those with no electrical service at all.

  5. Jon_R | | #5

    Sounds like you should install whatever option is least expensive - and then use a window instead.

  6. rockies63 | | #7

    According to the new BC Canada building code the ventilation system I have to install must run continuously 24/7. However, they do allow the use of a "Passive Vent" system if the house is less than 1808 sq' in size, is all on one level and doesn't have a basement or crawlspace (which is pretty much what I am building).

    The passive air inlets I'm considering are the Lunos ALD-R 160 units.

    I have to install one ALD-R 160 in the bedroom and one in the main common room. The cabin's exhaust fan can be the bathroom fan as long as it runs 24/7. I am reluctant to use the bathroom fan as the whole house fan since the bathroom door will probably have to remain open most of the time to equalize pressure between rooms.

    If I use an independent bath fan and a independent range hood fan then what whole house exhaust fan should I use? I'm not too concerned about heat recovery from the ALD-R 160's (or should I be?) but should I have heat recovery in the whole house exhaust fan? Is there such a device?

    1. Expert Member
      MALCOLM TAYLOR | | #8


      Where is the cabin? The passive vent opti0n can only be used in some climate zones.

  7. rockies63 | | #9

    The cabin is near Nelson BC in the Canadian Rockies. The BC building code says that passive vents can be used provided the average January temperature stays above -10 C (in Nelson the average is -3 C). Perhaps a heat exchanging vent would be better, but how much power would they use?

    1. Expert Member
      MALCOLM TAYLOR | | #10


      As I read the code it is not the average January temperature that is used, but the 2.5% January temperature. Using table C-2 of appendix C, the 2.5% temp. for Nelson looks to be -18c.

  8. rockies63 | | #11

    AAARGH! Well then, it looks like an ERV is required. Which unit would be the most suitable for an 800 sq' cabin built off grid?

    Oh thank you Govt of Canada for making me install one!

    1. Expert Member
      MALCOLM TAYLOR | | #12


      As I said in post #6 above, I'm not sure any mechanical ventilation is required.

    2. awilliamfrederick | | #14

      Hi Scott,
      I installed several of the Lunos E2 units before realizing how relatively simple they are, so I made my own with a 12v relay, ceramic soldering pads (which is all the “ceramic core” in the Lunos is), and two computer fans. (On another note, the Lunos comes with a schedule 40 pipe for a through wall duct, so you can enjoy the soothing aroma of PVC, but it’s easy to make your own 5 inch “duct” using aromatic wood veneer and make your house smell nice in the process.)
      By making your own, you can wire the 12v fans direct to your battery bank and avoid the self-consumption power that the inverter would be otherwise using up. Three separate units running 24 hrs a day consume about .252 kWh, around a tenth of the consumption that a normal HRV would consume in the same timeframe.
      Oh, and if I remember correctly, the total cost was around $130.

      1. Trevor_Lambert | | #18

        This seems like a really good idea for an off grid house. However, your numbers a little deceptive. The conversion losses from 120Vac to 12Vdc aren't going to be 90%. More like 10% or 20%. So the fact that your system uses one tenth the electricity means that it's also delivering far less airflow. Have you done any measurements on it?

  9. GBA Editor
    Martin Holladay | | #13

    Step one: Verify with your local building department whether the code requirement for mechanical ventilation system applies to off-grid homes.

    Step two: Remember that whatever equipment you are required to install, you don't need to turn the equipment on when you move in. It's your house -- you can't be required to run your fan for 24 hours a day if you don't want to.

  10. MAinspector | | #15

    If continuous ventilation is a code requirement for a new dwelling, how can someone recommending not using it? There are countless articles on GBA speaking to the importance of ventilation for the health of the occupants and the building itself but how is it only important on a grid tied house?

    My point of view would be that the energy needed for the mechanical ventilation is a necessary load that must be figured into the total energy consumption of the house. Not something that can just be omitted because its tough to comply with. How about running the ventilating equipment at a higher rate during the day when the PV system is producing? As long as it met the "24 hour" requirement in 12 hours, it shouldn't have to be "continuous".

    1. Expert Member
      MALCOLM TAYLOR | | #17

      - The only disadvantage of using windows to ventilate houses instead of mechanical systems is an energy penalty, as you invariably over-ventilate and can not condition the incoming air. This is how all houses were built until very recently.

      - It's worth noting that "off-grid " also refers to perfectly legal residences with no source of electrical power.

      - In for a penny, in for a p0und. If the requirements did apply, you can't cherry pick how you want to meet them. Continuous ventilation can't be supplied intermittently.

    2. Trevor_Lambert | | #19

      You can't just average the ventilation rate over 24 hours. With no ventilation, the CO2 levels are going to rise significantly within a couple of hours. I know, because I've measured it; and I was in a 2400sqft house, a <800sqft house is going to be three times as bad. By the 12 hour mark, it's going to be very grim. Then it's going to take several hours at a fairly low CFM rate to get back to healthy levels. Just in time for you to get home from work, and enjoy a couple of hours of good air quality before starting the cycle all over again. Repeat until it's warm enough outside to open the windows.

      By the way, unless you're on the equator, in which case none of this matters, the ratio of daylight to nighttime hours in winter is going to be much worse than 12/12; it will be anywhere from 10/14 down to 7/17.

  11. GBA Editor
    Martin Holladay | | #16

    If you are moving into an off-grid house, you are moving away from civilization. You aren't exactly camping, but you're definitely not in suburbia anymore. Off-grid life is not the same as life in the suburbs.

    When you go backpacking, you don't expect to sleep in a queen-size bed with springs and a mattress; nor do you expect to have a hot shower every day.

    If you want a modern house with 24-hour-a-day ventilation, off-grid life probably isn't for you.

    My wife and I sleep with the window open a crack, even in winter. It works for us.

  12. MAinspector | | #20

    I just don't understand the mentality that and an "off grid" house somehow gets you a pass from complying with building codes. It really doesn't matter where it is and it doesn't matter that the current occupant may have a work around for keeping the building healthy. Just my opinion...I rely on GBA for a lot of insight and advice and appreciate the mentality of going above and beyond building codes but advice to disregard them is where you lose me. Trevor is saying that after 8 hours C02 levels could be bad but Martin is saying just turn the ventilation off and open a window. Will everyone that ever sleeps in that house know they need to open a window every night?

  13. GBA Editor
    Martin Holladay | | #21

    Green Building Advisor has always taken the position that builders should always comply with building codes. That's why I advised Scott (in my Comment #13) to "Verify with your local building department whether the code requirement for mechanical ventilation system applies to off-grid homes."

    My observation that homeowners are under no legal requirement to operate their ventilation systems for 24 hours per day has nothing to do with off-grid homes. That's always been the case, whether your home is off-grid or grid-connected. In the U.S. and Canada, there are no laws compelling homeowners to operate their ventilation systems any particular way -- and we don't yet have "ventilation system operational mode police." All we have is code inspectors.

    If you want to lobby your legislators to establish a ventilation police force to make sure that homeowners keep their fans on for 24 hours per day, feel free to do so.

    I strongly advise GBA readers to supply plenty of fresh air to their homes, especially in bedrooms. I can provide links to articles on the topic if you want to know more. I keep my window open a crack when I go to bed to ensure that CO2 levels aren't dangerous.

    Off-grid homes make up a very tiny percentage of North American homes -- well under 1%. Those of us who live in the woods, far from electric lines, represent a minuscule and shrinking minority of North Americans. But thanks for your concern about our health.

    1. Expert Member
      MALCOLM TAYLOR | | #22

      One of the things I noticed poking through our code on this topic was the injunction that where electrical service was available, it had to be installed in buildings. I guess the spaces on the margins for living off-grid are being further diminished.

      1. GBA Editor
        Martin Holladay | | #23

        One more thought on the topic: Assuming that you live somewhere where it is still legal to build an off-grid house -- a cabin in the woods, so to speak -- I can't imagine that any code would require the installation of an off-grid electrical system. Off-grid homes still exist without any batteries at all -- relying on kerosene lamps. An elderly woman on my road still lives that way, in a house without a battery or a PV array. She reads by kerosene lamp.

  14. rockies63 | | #24

    Given all the back and forth on whether a ventilation system is necessary, when to turn it on, when or if you should turn it off, etc, it's unfortunate that only Andrew mentions any specific product that could be used (I'm not sure if a homeowner-built device would be approved, although I wouldn't mind seeing a diagram and parts list on how to build one).

    In looking at various units the Panasonic WhisperComfort Sport ERV (model FV-04VE1) seems to be the best option. The literature recommends that the unit be set for a 40 cfm flow rate (using 23 watts) and it can be used in my climate zone (although it is rated to run "optimally" from April thru Nov and alternates between "balanced and exhaust only" from Dec to March when the temperature is below freezing). I guess I'd have to open a window a bit during the winter in order to balance the pressure?

    Perhaps I could add a sensor that adjusts the flow rate to a lower capacity during the night, if that's possible. Or perhaps a different product would be better?

    Martin, I will check with the building department about whether a ventilation system is even necessary but I have read several articles on this site discussing the fact that opening a window is not enough to properly ventilate a house. (I think you even wrote one - I'll have to check my Holladay collection). :)

    There's also the issue of balancing the house when the bathroom fan and range hood fan are being used. I'd rather find the right product than having to think about opening and closing windows, setting timers, or worrying about excessive battery usage whenever I turn on a fan.

    1. joshdurston | | #26

      I think you need to figure out if you are installing equipment just to meet some code requirement, or if you are doing it for yourself, or both. And also how much you are willing to actively manage it.

      It sounds like you are looking for an excuse to install a fancy ERV reading between the lines.

  15. GBA Editor
    Martin Holladay | | #25

    If your house is grid-connected, it's certainly best to include a mechanical ventilation system rather than relying on windows for ventilation.

    But Scott, you are building far from the powerlines, and you evidently are about to move into an off-grid house. Everything is about to change for you. Learning when to open your windows a little crack is just the beginning of your adventure. Good luck!

  16. rockies63 | | #27

    Josh, I am not looking for an excuse to install a fancy ERV. If I wanted one I'd install one. What surprises me is that I seem to be required to install one by the BC building code. I will check with the building department to ask if their statement "mechanical ventilation is required for all new buildings supplied with electrical service" means for only "grid-tied" buildings or not but if I am required to install one then I'd like to find out which one is the best one to run off of a PV solar system.

    1. Expert Member
      MALCOLM TAYLOR | | #28


      Even if you were required to provide mechanical ventilation, you wouldn't be required to install either an HRV or and ERV. All the code calls for is a certain CFM, and this can be exhausted by the bathroom or kitchen fans you already intend to install. The only additional step necessary would be a supply fan.

  17. canada_deck | | #29

    @Scott ,
    Re: "According to the new BC Canada building code the ventilation system I have to install must run continuously 24/7."

    I am unaware of this. Do you have a source for this info?

    1. Expert Member
      MALCOLM TAYLOR | | #30

      It's in the recent revisions to the BC building code. A summary can be found in the last link of Scott's post #4.

      1. GBA Editor
        Martin Holladay | | #31

        Is it required for builders to install equipment that is capable of running continuously, 24/7? Or is there actually a requirement that compels homeowners to use it that way?

        1. Expert Member
          MALCOLM TAYLOR | | #32

          The requirement is :
          "Every dwelling unit needs to have one fan that exhausts air continuously (24hr/day) at the minimum exhaust rates outlined in Table This principal exhaust fan may double as a kitchen or bathroom fan, or it could be an additional fan installed anywhere in the dwelling unit."

          However they anticipate owners turning it off. There is a stipulation that the switch for the main ventilation system be in a prominent place and clearly identified so as not t0 be confused with the controls for other fans like bathroom exhausts.

          It's both a sensible ventilation requirement, and as you say, one which you can easily bypass if you would rather open a window, or run the system intermittently.

          1. GBA Editor
            Martin Holladay | | #33

            Thanks, Malcolm.

      2. canada_deck | | #34

        Thanks Malcolm.

  18. rockies63 | | #35

    In looking through this article describing the technical requirements for ventilation it states under heading (sentence 3 - points A and B) that the ventilation exhaust fan has to run continuously and be fitted with a switch that can only be turned on or off (and stated elsewhere that the fan can only be turned off for the purposes of cleaning or repair).

    However, there is also a section describing "Non-Heating Season Natural Ventilation" requirements (section 9.32.2) which seems to suggest that the mechanical system can be switched off during the summer. There is also a section describing the requirements for kitchen range hoods and bathroom fan ventilation requirements (section

    One question I have about section is the requirement for additional make-up air in the case of using an exhaust fan to vent a gas appliance. I'm wondering if that applies to make-up air for a range hood over a propane stove?

    One interesting thing I see mentioned in this document has to do with Passive supply venting requirements. In comment #9 of this thread I mentioned that "passive vents can be used if the average Jan temperature stays above -10C" (which it does in Nelson BC) but in comment #10 Malcolm corrected me by saying that "the 2.5% temp for nelson was actually -18C". According to section (sentence 6 -A-1) the 2.5% temperature has to be higher than -20C, not -10C. That may put passive supply venting back on the table.

  19. PAUL KUENN | | #36

    Scott, I can vouch for the Lunos. Ours are 5 years old now. Only 1 pair. Switched at 10, 15 & 20 cfm, they keep our house very comfortable with never going above 50% humidity level. 1200 sq./ft. house. .8 ACH/50 P very tight. I threw away the wall wart and it run's directly off 12V PV battery. About 15 watts average. We turn it off spring - autumn as we like windows open. Lots of plants and citrus plants watered indoors in winter. Proof is in the pudding.

  20. Expert Member
    MALCOLM TAYLOR | | #37

    Off Grid Buildings In Canada

    In at least two of the larger provinces (BC and Ontario) the Building Branches have interpreted "providing (or supplying) electricity" as including on-site generation.

    The thinking behind this seems to be that the systems and storage are quickly evolving to the point where their capabilities closely mirror those on grid-sourced power. Since these homes will to all intents and purposes be indistinguishable from their neighbours, they should not be exempt from any of the provisions of the building code, especially those related to the safety of occupants.

    This does appear to be another circumscription of the traditional off-grid world people like Martin have enjoyed.

    Edit: Seasonally occupied residences still appear for now to be exempt from many code requirements.

    1. GBA Editor
      Martin Holladay | | #38

      Off-grid homeowners in Vermont have a variety of tricks to help get them through November, December, and January. When the voltage drops, we often cut back on lighting or appliance use, hoping for a rare sunny day to resume using the luxuries. If we have a generator, the generator doesn't always work. Sometimes the generator is in the shop.

      Will the electricity police come to our door and order us to make more electricity? If they show up, how am I supposed to make it?

      1. Expert Member
        MALCOLM TAYLOR | | #39


        This all only affects new residential construction - and as we discussed in the original thread, the code only mandates what equipment needs to be provided, not that y0u use it.

        So in Scott's case, he needs to have smoke detectors, lighting, an electrical panel large enough to service the potential loads, ventilation, etc. included in his build. But I don't even see anything saying he needs to provide a source of electricity capable of running them all. he could live as you do, opening the windows and being frugal with energy use, but the house is set up so that in the future it is capable of either being attached to the grid, or being powered by some alternate source without having to be modified.

  21. bentkibler | | #40

    I'm also building an off grid, tightly sealed cabin, and looking for a highly efficient HRV/ERV, preferably a through wall. I think Martin mentioned Twinfresh a while back as a cheaper alternative to Lunos. Anyone with firsthand experience with Twinfresh in an off-grid setting?

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