GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

ERV or HRV (yes, bringing it up again)

this_page_left_blank | Posted in Mechanicals on

I’ve read all the articles and posts I can find on here about this question, and if anything I feel less able to make this choice than before. So many conflicting opinions. Here are the factors that affect the decision, as far as I can surmise:
-predominantly heating climate, but mixed and with hot, humid summers (SW Ontario) <-points to ERV? -medium sized house? 2430 square feet, no basement -3-4 occupants, higher than average humidity generation (not a lot of showers, but lots of cooking/baking – think 1950s housewife levels, then add some more) <-points to HRV? -tight house (<=0.2ACH@50 expected) -no air conditioning, other than tempering of incoming air via glycol ground loop -no forced air (besides the HRV/ERV fan) -ERV/HRV must exhaust the kitchen and bathrooms <-points to HRV, at least in winter? The original design called for a model of ERV we probably cannot get, which has this claim in its literature: “Futura will automatically maintain the optimum humidity in your house by means of a controlled enthalpy exchanger.” I can’t figure out if this means it’s actually smartly controlling the humidity exchange, or if it’s just marketing baloney. My previous understanding was that an ERV will, while not cooling the house, definitely reduce the heat gain in the summer. But I read lots of stuff on here suggesting that without A/C, it will do nothing. This doesn’t square with the fact that ERVs have a cooling efficiency rating, while HRVs don’t. Don’t know what to think anymore. :-/ Any advice for our particular conditions?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Yupster | | #1

    An ERV only transfers a percentage of the moisture in the air in one stream to the air in the other stream. The moisture will go from high humidity to low humidity. So for a house with no air conditioning, if you had a very tight building envelope and you opened your windows at night to let fresh, less humid air into the house, then through the day the ERV would help keep your ventilation air from bringing in more humidity. If the air inside is the same humidity as outside, it will do nothing for humidity control. Same thing for air temperature. You have to have a difference in temp for an HRV or ERV to do anything aside from provide fresh air in the summer. Your cooking/baking moisture should be controlled with a range hood. Most people welcome the additional humidity an ERV provides in the winter. A very tight house does not usually have the same low humidity issues, so that's a decision you'll have to make. If you are really worried about it, just pick an HRV with a swappable core. Vanee 90H-V ECM is a decent HRV that you can swap out the core and make it an ERV for $100 last I checked. Might put your mind at ease having that option.

  2. GBA Editor
    Martin Holladay | | #2

    Q. "My previous understanding was that an ERV will, while not cooling the house, definitely reduce the heat gain in the summer. But I read lots of stuff on here suggesting that without A/C, it will do nothing. This doesn't square with the fact that ERVs have a cooling efficiency rating, while HRVs don't."

    A. ERVs bring outdoor air into your house. If the outdoor air temperature is warmer than the indoor air temperature, operating an ERV will make the indoors hotter. The longer you run the ERV, the more heat you introduce to the house. So an ERV is incapable of "reducing the heat gain in the summer."

    If you have an air conditioner, operating an ERV also brings heat into your house and makes your air conditioner work harder. But it won't cause as much of an energy penalty as an exhaust-only or supply-only ventilation system (that is, a ventilation system without heat recovery).

  3. this_page_left_blank | | #3

    You said "If the outdoor air temperature is warmer than the indoor air temperature, operating an ERV will make the indoors hotter."
    Isn't this only compared to if you don't bring in air at all? This isn't an option. When compared to opening a window, or some other way of bringing in the air "as is", the ERV will heat the home less.

  4. this_page_left_blank | | #4


    I've toyed with the idea of a swappable core, I know that Zehnder has them but I think they're more like $500. I wasn't aware vanEE had them as well. The 90H model doesn't come close to meeting the code requirement for ventilation for our house, but I'll see if their other models have this option. The range hood doesn't vent to the outdoors (as is pretty standard practice for passive house design, as far as I can tell).

  5. ohioandy | | #5

    Trevor, like so many decisions in the green building scheme, this one can go either way, and it comes down to your priorities and prejudices. You didn't mention a primary factor: cost to install and cost to operate. HRV is cheaper.

    I was born and raised in southern Ontario, and let me humbly challenge your assertion that you have "hot and humid" summers. Those few days or odd weeks that it's slightly uncomfortable simply don't compare with the stinking heaviness of the lower climate zones, where I was dragged by marriage. The HRV/ERV debate on this issue generally rages in the humid parts of climate zone 4 and points south.

    If your tightness goal is 0.2 ACH50 in (US) climate zone 6, you don't need any kind of sophisticated humidity control, rather you will be fighting tooth and nail for 6-8 months per year just to evacuate humidity from your house. The rest of the year, just keep your windows open.

    I'd say a high-end HRV is a no-brainer. (But that's me, with my priorities and prejudices.)

  6. this_page_left_blank | | #6

    I agree that in comparison to southern climes, it's neither hot nor humid here. But it's hot and humid enough that bringing in the humid air from outside is undesirable. My bias comes in to effect since I came from Calgary, where it is dry in the summer. I think my biggest concern is over-humidifying in the winter, in which case you're probably right, the HRV is best. Curious though as to why you say the ERV costs more to install? I know it's more to operate, since the membranes would need replacing and it's slightly lower energy efficient (although that is variable, lots of HRVs out there are much lower in efficiency than many ERVs).

  7. Yupster | | #7

    The Vanee 90H-V ECM produces 157 cfm at high speed at 0.4 ESP. Assuming even a 5 bedroom house, your principal ventilation rate would be 90 cfm, well within the range of the equipment. If you are looking to meet your total ventilation rate with your HRV/ERV, then that's a different case. Can I ask what ventilation rate your hvac designer has spec'ed? I'm going to agree with Andy here though, and say an HRV would work fine for you in our Ontario climate.

  8. this_page_left_blank | | #8

    Yes, we are getting all our ventilation from the ERV/HRV. The design spec'd out requirement of 117cfm. We are shooting for 150-200, for temporary boost purposes. I was looking at the wrong column on the 90H spec sheet (under energy performance instead of ventilation performance). So yes, it can handle the flow requirement, but I would probably rule it out based on efficiency (68% at 117cfm is pretty poor). Oddly, the HRV version of the one I was considering (G2400x ECM) has a lower efficiency than its sister ERV.

    I should also say I don't agree with the 117cfm, which is higher than I get when I plug the numbers into either the ASHRAE formula (103) or the BSC formula (84). But the target for boost ventilation is still 150 in any case.

  9. lance_p | | #9

    ASHRAE 2010 requires (#bedrooms +1 x 7.5) + (sqft x .01), so (3 + 1 x 7.5) + (2430 x .01) = 54 CFM assuming 3 bedrooms. The 2010 standard is what's being enforced here in Ottawa right now. Check with your local officials.

    Installing an HRV usually costs more than an ERV since an HRV requires a drain for condensation, which can also limit placement options or require a condensate pump.

    The smaller/tighter the house, the more occupants and the more humidity generated, the more the argument leans toward an HRV. The bigger/leakier the house, the fewer occupants and the less humidity generated, the more the argument leans toward an ERV. Having never lived in a tight high performing house I've always dealt with low winter humidity, so my prejudice leans towards an ERV. Those with experience in tight houses tell me this is less of an issue for them. The above statements are true and where your situation falls is an unknown beforehand. The swappable core ventilator makes a lot of sense as long as the efficiency meets requirements.

    Speaking of requirements, you'll need to know which compliance package you plan to meet to get your building permit. The minimum efficiency requirements for HRV/ERV are listed in Supplementary Standard SB12:

    An ERV will help reduce cooling load in the summer by transferring moisture from the incoming air to the outgoing air. This was proven here in Ottawa at the NRC Canadian Centre for Housing Technology where they noted a reduced consumption of 12%:

    This is only possible if the outgoing air has lower absolute humidity than the incoming air, which will not be the case in a house without air conditioning or some other form of dehumidification.

    Don't let anyone tell you that Southern Ontario isn't a humid climate in the summer, it certainly is! It's certainly not the hottest place, but it is definitely humid. Personally, I can't imagine living in a house here with no AC... even with windows open 24/7 the humidity would be extremely uncomfortable. For the cost, a small mini split running in Dry mode would be invaluable and would provide some cooling as well. My $.02

  10. this_page_left_blank | | #10

    I find it interesting that Ottawa is using numbers from the 2010 ASHRAE 62.2, since it directly contradicts the Ontario Building Code, section 9.32. This is what our HVAC designer used to come up with the 117cfm number, and what our building inspector cited to me as well. I think the OBC is out to lunch, since it takes into account rooms other than bedrooms (and irrespective of total square footage), so if you had a small house with small rooms the number's going to be similar to a large house with large rooms. But it's pretty hard to argue against the building code.

    I've spent the last 7 years living in two different houses without A/C. Well, technically they both had A/C but I was forbidden to operate it unless the interior temperature hit 29C. These were both terribly insulated, poorly designed houses. If those were survivable without a/c, this house should be fine. I got a quote on a mini split, and even with a hefty rebate it was still $3000. Honestly, with the judicious use of blinds and night time ventilation, I will be very surprised if the house ever gets above 25C. Time will tell.

  11. lance_p | | #11

    Trevor, check out Principal Exhaust:

    "(5) The principal exhaust required in this Article may be provided by means of a heat recovery ventilator installed in accordance with Article"

    Table lists 30 and 37.5 L/s for three and four bedroom dwellings, respectively, which converts to 64 and 79 CFM.

    Section 9.32.3. Mechanical Ventilation seems to be referring to combustion appliances. Is there a chance your people are referring to the incorrect section of the building code? Perhaps the reasoning is because you have no bath fans and no range hood exhaust? Ventilation of Rooms and Spaces, states that mechanical ventilation is required for rooms without natural ventilation (windows). If you're building a house without operable windows they might have a point, but if you do have operable windows then I don't see why you would be held to those ventilation rates? Maybe there's something in the code I'm missing?

  12. this_page_left_blank | | #12

    It's a very convoluted document, as most code documents seem to be. The principal exhaust is 63.6cfm, no argument there. However the principal exhaust is only part of the total ventilation capacity.

    " (1) The minimum total ventilation capacity of the ventilation system required in clause shall be the sum of the individual room capacities given in table" I won't try to reproduce the table here, but it includes every possible room description you can think of plus "other habitable rooms". In other words, aside from closets, every room in the house counts. I think this is monumentally stupid, but there it is.

    Section 9.32.3 does seem like it has something to do with combustion appliances, because in they classify the house types based on presence and type of various combustion appliances. But the upshot of all of that is in, it says for type 3 houses the system must comply with part 6, all other types (including houses with no combustion appliances) must comply with this (9.32.3) subsection. So taken at its word, the code does indeed seem to be saying that every house must follow table, at a minimum (I can only assume the requirements are higher for type 3 houses).

    Interestingly, if you read the clause they reference in, that is, it says:
    "Every dwelling unit that is supplied with electrical power shall be provided with a mechanical ventilation system in accordance with subsection 9.32.3." According the OBC, every new house must have a mechanical ventilation system (unless you have no electricity, which itself probably prevents it from being considered a dwelling unit). I don't think this is being enforced very many places.

    Now for the really convoluted part, seems to contradict with 9.32.2. It basically says each room must be ventilated either by natural or mechanical means. Natural means is describes as basically an operable window, and there's a table describing the minimum size relative to the room size. So as long as the room has a operable window, or is connected (without obstruction, i.e. a door, to another room that has a window, those rooms don't need mechanical ventilation. So mechanical ventilation is required for a room that has no window, and can be closed off from any rooms that do. Sort of makes sense, except the fact that it requires mechanical ventilation shouldn't affect the total ventilation requirement for the house, because ultimately the air in that room is coming from the rest of the house. The fact that you closed the door doesn't increase the whole house ventilation requirement. I am left to wonder what they think happens when you close the door in a room with a window but the window's closed? I imagine the next revision of the code will require an interlock that automatically opens the window when the door to that room closes.

    So yeah. In the end, I agree that our designer has possibly misinterpreted the code and allotted mechanical ventilation to rooms that don't apply.

    Edit: It just occurred to me that the mechanical ventilation system requirement could probably be satisfied by just having a bathroom fan. I wouldn't consider this a "system", but that's probably what the common interpretation is.

  13. Yupster | | #13

    All that code jibberish is basically allowing for an exhaust only ventilation system. You put bathroom fans in your rooms without windows, typically only bathrooms or laundry rooms. You put a range hood in the kitchen. You provide your PVC and your TVC with those. You have windows for natural ventilation of spaces because an exhaust fan doesn't guarantee that all your spaces will see that fresh air, really just the leakiest places. allows a designer to use Part 6 rather than Part 9 for any single family dwelling, giving the designer more flexibility to comply with other standards.

    And I see now that you caught on to the bathroom fan system already...

  14. lance_p | | #14

    Leave it to the Gov't to provide us with such clear direction! LOL

    I'm going to go back to the City code officials and get a more comprehensive answer for our house based on this conversation. I definitely don't want any surprises at the last minute.

  15. user-7323101 | | #15

    Hey Trevor,
    Just curious what you ended up deciding on this. I am currently building my passive house in Wasaga Beach and have same size house and same amount of people. Any chance we can get in contact? My cell is 705 716 4231. [email protected]. That would be greatly appreciated. Some of the other questions you posted are also things that I'm wondering about and would love to hear your advice since by now you probably went through all of that.

    Best Regards,

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |