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Six Steps to Success With Heat-Recovery Ventilation

Whole-house ventilation is one of the cornerstones of a high-performance house

One of the most visible, and perhaps even iconic, features of a super energy-efficient home is the heat-recovery ventilator (HRV) or its close cousin the energy-recovery ventilator (ERV). Both remove stale air from the house and replace it with pre-conditioned fresh air from the outside.
Image Credit: National Renewable Energy Laboratory

Heat-recovery ventilators (HRVs) and energy-recovery ventilators (ERVs) remove stale air from the home and replace it (in winter) with preheated fresh air from outside. The result is better indoor air quality and lower energy use than in standard homes. The HRV itself is fairly simple: an airtight box with a heat exchange core that transfers heat from the indoor air to outside air (or vice-versa) as the air passes through the box. The box also contains two small fans to move the air. All the points below apply equally to HRVs and their close cousins, energy-recovery ventilators (ERVs). This article is based on training developed by Bruce Manclark and Dan Wildenhaus of CLEAResult. This is the first of two parts. Part 2 will cover integrating HRVs with forced air heating and cooling systems.

Ventilation is essential in all modern homes. When homes are built with energy efficiency in mind, they are more tightly air sealed than the average building and therefore need fresh air distributed through the entire home. A central ventilation system exhausts stale indoor air from high-moisture areas, such as bathrooms and kitchens, while simultaneously supplying fresh air to living areas and bedrooms. Central ventilation also offers the option of filtering the outside air to remove particulates, allergens, and chemical pollutants. The result is well-distributed fresh clean air.

All homes pay an energy penalty for ventilation, because air that sneaks in through cracks and openings must be heated or cooled. Very airtight construction combined with central ventilation systems offer the opportunity to preheat incoming air in winter by transferring warmth from the stream of outgoing air. A heat exchanger can capture between 70% and 95% of that heat to reduce the energy needed to heat incoming air – something that is especially valuable in colder climates.

While most HRV equipment is well-designed and durable, the technology has been plagued by poor installation practices that reduce their value. “In all my many years in the HVAC industry,” says Bruce Manclark of CLEAResult, “I have never seen anything screwed up as much as HRVs.” Here are the six steps to success for selecting and installing HRVs.

1. Calculate required air flow

The amount of fresh air flow for any type of ventilation system is calculated according to a national standard known as ASHRAE 62.2 – 2010, which takes into account both the number of occupants and the conditioned floor area of the home. The simple equation goes like this:

(Occupants x 7.5) + (square feet of conditioned floor area x 0.1) = ventilation rate in cfm

So, four people living in a 2,000-square-foot home would need a continuous air flow of:

(4 x 7.5) + (2000 x 0.01) = 50 cfm

This formula will get you close enough, but if you want to be even more precise, there is a sophisticated online calculator that allows detailed inputs for more exact results.

2. Select efficient equipment

HRVs have internal fans that run many hours a day and sometimes continuously. You should choose a model that provides the necessary air flow while sipping as little energy as possible. HRVs should be tested and certified by the Heating and Ventilating Institute. Most manufacturers show these testing results in their product literature. A great way to compare products is the online version of HVI’s Certified Products Directory.

To choose an efficient model, first find the sensible recovery efficiency (SRE) column in the HVI directory. This shows how efficiently the unit transfers heat between air streams. Look for an SRE of at least 80%. This value is clearly shown in the database. Next, you’ll need to calculate how efficiently the unit moves air. This is called efficacy and is expressed as cfm per watt. While this number does not appear in the database, you can easily calculate it by dividing Net Airflow (cfm) by the Power Consumed (watts). You want the efficacy to be at least 1.25 cfm per watt.

3. Locate exhaust points

Since the idea is to remove humid, odiferous air from the house, locate the stale air exhaust points in each bathroom, kitchen, utility room, and other high moisture areas. This allows heat recovery from areas of the home where humidity and odors are most abundant. The HRV can replace spot ventilation (exhaust) fans in these rooms to save money and provide a more pleasant environment. If homeowners are fond of a steamy shower, but averse to a foggy mirror, a standard bath fan can be installed to supplement the HRV.

An exhaust point located near the kitchen area should be at least six feet from the cooking surface. This exhaust point is intended to remove general moisture and cooking odors. While HRVs are not intended to entirely replace the range hood, in some applications, with an HRV in the kitchen, it may be possible to eliminate the external venting on a range hood and operate it in recirculation mode only. As with bathroom spot ventilation, occupant habits may dictate a standard range hood in the kitchen to expel moisture and odors.

4. Locate fresh air supply points

In order to mix fresh air throughout the house, supply points should be positioned a considerable distance from the exhaust points. Bedrooms and living rooms are good choices. Even though incoming fresh air has been tempered by the heat exchanger, during the winter the fresh air is usually slightly below room temperature, so take care not to make occupants uncomfortable by blowing that air directly onto them. Place the incoming vents high on a wall, so it will mix with warm air and not be noticed. In a bedroom, introducing fresh air into a closet allows gentle mixing with room air. Plus, it has the added benefit of helping keep the clothes smelling fresh and clean!

5. Create a dedicated duct system

Most experts agree that it’s best for an HRV to have its own dedicated duct system. If the home has hydronic heat or ductless heat pumps, that’s the only choice. In this case, the HRV mixes the air throughout the house. However, homes with forced air heating and cooling systems can share the ducts used for heating and cooling. This saves money on material and labor and offers great distribution of fresh air. Integrating HRVs with forced air systems requires careful planning, proper controls, and sound installation practices. Manclark covers these issues in detail below.

6. Decide on an HRV or ERV

The information above applies to both HRVs and ERVs, which may perform equally well in most climate zones. But what is the difference between a heat recovery ventilator (HRV) and and energy recovery ventilator (ERV)? The main difference is that an HRV transfers only the temperature of air between the outgoing and incoming air streams. Engineers call this sensible heat. It’s the heat you feel directly as a change in air temperature.

But air always contains some water vapor and that vapor also holds energy. ERVs transfer sensible heat plus a substantial amount of water vapor between the incoming and outgoing air streams along with the energy in that vapor, a property called enthalpy. Because ERVs capture this additional form of energy, their efficiency ratings are generally higher than HRVs.

But wait! Isn’t the purpose of ventilation to remove humidity from a home? Why have a device that returns some of the water vapor? Some climates are very dry and will benefit from this feature of an ERV. This can be useful in many inland areas of the American West. In the American Southeast, the situation is reversed, but an ERV is still appropriate. Here, the indoor air has been dehumidified, so ventilation would introduce outside air with a much higher relative humidity. In this case, the ERV expels the humidity back to the outside and helps maintain a lower indoor humidity.

These two examples may seem contradictory. In one case, humidity is maintained inside the home and, in the other case, humidity is expelled. However, in both cases, the water vapor jumps across the core, from the more humid air stream to the less humid air stream and returns to where it came from originally. Consistent with basic physics, the water vapor moves from a higher concentration to a lower concentration.

If you follow these six steps to selecting the right equipment, you’ll be on the right track to achieving better indoor air quality and greater energy efficiency. For more details see the HRV System Best Practices Poster at

This post originally was published at the Zero Energy Project and is used here with permission.


  1. Randy_Williams | | #1

    Even in a tight home, there
    Even in a tight home, there is some air leaks. Can and should those be taken into account when sizing the HRV or ERV? Is there a way to adjust an HRV or ERV's CFM settings after installation? Maybe your household has reduced from 4 people to 2 people, a reduction of 15 CFM per ASHRAE 62.2.

  2. GBA Editor
    Martin Holladay | | #2

    Response to Randy Williams
    Ventilation equipment installers almost always size their equipment according to the ASHRAE 62.2 formula. The ASHRAE 62.2 formula doesn't depend on the leakiness of the home's envelope -- just the number of occupants and the number of square feet. [Later edit: This isn't the whole story, however. Note John Semmelhack's comment below.]

    HRVs and ERVs almost always include controls that allow you to choose the ventilation rate. Most HRVs and ERVs have multiple speeds, so you can select the speed that makes sense. Some manufacturers also include timers that (for instance) allow you to program the unit to ventilate for 20 minutes per hour. If the unit doesn't have a timer, you can just buy a timer and plug the unit into the timer.

    In short, you can vary the ventilation rate (or even turn the whole thing off, if you want).

  3. user-626934 | | #3

    ASHRAE 62.2
    Martin - ASHRAE 62.2-2013 and 62.2-2016 have an option to include the actual leakiness of the house (using blower door test result as the proxy). Both of these versions increase the per square foot ventilation to 0.03cfm/ft2 (compared to 0.01cfm/ft2 in 62.2-2010) and then allow a reduction of that rate based on the blower door test result.

    Easy online calculators can be found here:

  4. GBA Editor
    Martin Holladay | | #4

    Response to John Semmelhack
    I stand corrected. Thanks for setting me straight.

  5. user-7005952 | | #5

    Typo in formula
    There may be a typo in the formula for step 1. 0.1 is used in the first formula but 0.01 is used to calculate the value for the 2000 sq ft house.

  6. Jon_R | | #6

    There is probably an economic
    There is probably an economic argument for a smart HRV that reduces output as the wind increases.

    > you can select the speed that makes sense.

    But good luck finding data on what makes sense.

    In cases where there are open doors, I can't convince myself that HRV vent location makes a significant difference. Ie, flow through the doorway greatly exceeds HRV flow.

  7. GBA Editor
    Martin Holladay | | #7

    Response to Michael Maines
    You wrote, "I'm curious why sensor-driven ventilation is not promoted more often."

    I could propose several explanations. But sensor-driven ventilation violates the "keep it simple, stupid" principle, and complicates service calls and repairs.

    What do I think of power-adjusted rear view mirrors on cars? They're great, until you realize that a $49 mishap (in 1990) just turned into a $490 repair bill (in 2018).

  8. Expert Member
    Michael Maines | | #8

    On a Very Good House (a PGH
    On a Very Good House (a PGH that will be net zero energy) currently under construction we are using a Zehnder HRV, sized per ASHRAE 62.2 (both 2010 and 2013) and Passivhaus, which all happen to match pretty closely for this project. But we are also going to install sensors for relative humidity and carbon dioxide levels, so the owners can keep the fan running as little as necessary.

    At the other end of the spectrum, I recently consulted on a conditioned crawlspace for a modular home. On that project we will have a fan and return grill so the crawlspace will share air with the living space, with the ability to have it running continuously (to meet code) but also on a humidistat so the owner can choose to have it run only when it's actually needed.

    I'm curious why sensor-driven ventilation is not promoted more often.

  9. Expert Member
    Michael Maines | | #9

    That's a good point, Martin,
    That's a good point, Martin, and honestly the decision on this project was driven by the tech-savvy owner. Your mirror analogy is a good one, but would you say the same for replacing a simple carburetor with a computer-driven fuel injection system, and its associated improvement in efficiency and emissions? Appropriate technology and all that...

  10. GBA Editor
    Martin Holladay | | #10

    Response to Michael Maines
    Swapping out an old rear-view mirror used to be easy. All it took was a screwdriver. You went to a junkyard and found the right car, and unscrewed the old mirror.

    Adjusting a carburetor, however, was always a pain. I could never get the fuel/air mixture where I wanted it, and the floats would stick. So I'm no fan of carburetors.

    When it comes to the KISS principle, it could be argued that fuel injection is a simpler technology than a carburetor.

  11. SwitchgrassFarmer | | #11

    Sensor-Driven Ventilation - Experience
    For the last couple years I have been controlling my HRV with a commercial Honeywell CO2 Monitor and Economizer Controller, both bought off eBay. The sampling is done on the exhaust port on our ducted HRV.

    I have these controls set to run the HRV on high when the CO2 levels exceed 700 ppm, switch back to low at 600 ppm. It works exceedingly well; it will toggle the HRV to high if we have house guests, if I run the oven in our gas range for a long period of time, etc.

    No, it's not simple, now. I can see how with the proliferation of devices that are IoT ready (Internet of Things) that it can and likely will be in the future.

    For example Airthings has announced a new combination CO2, VOC, Radon, and Humidity monitor: They also have a hub in the works to link all these devices. So, in not long, a network of Airthings monitors in a home may be able to talk to an ERV/HRV.

    1. schreib77 | | #34

      amazing Andrew. I have been doing a low tech version of this. I bought a similar CO2 / humidity RH unit and move it around my home to understand what's happening. Great idea to close the loop like you did. Why in the world haven't the HRV manufacturers caught on??! Mine cost $250, an OEM price would probably be half that. Wouldn't you think they could get fantastic sales benefit by incorporating it as a monitor alone. Closed loop control would blow all other HRV's out of the market. . . if people understood the advantages.

  12. user-7005079 | | #12

    Centralized vs Decentralized Question
    Timely article for me... I read the section on decentralized units like the Lunos setup from Germany in a separate part of the the website. Any further musing on centralized vs decentralized other than the avoidance of ducts and personal tastes? Thoughts on more holes (I would need 3 pairs/so 6 holes in the walls) with a decentralized unit?

    Thanks - Raymond/(planning for Fraser, Colorado; 7a climate zone)..and new to the site

  13. schreib77 | | #13

    KISS is a good idea, but let's keep it cheap too.
    I get a big kick out of the running advice over which expensive air exchanger to buy, then add on little tweaks and then admit outright that the REAL users subvert much of this apparatus anyway. I am a realist and a mechanical engineer. I just built a new home, very tight, not as tight as the PassivHaus standard-- blower door rate of 1.0, at 2700 sq ft, slab on grade, two humans. So, per ASHRAE I should be mechanically ventilating 24/7 @ 42 cfm . I COULD have spent a few thousand dollars installing one of these contraptions to make the code guy happy at the state but found out all I REALLY was being required to do was ventilate the same rate in as out-- 42 cfm. NO requirement for a heat exchanger, filters, defrosters, humidity control, pressure control, long octopus runs to various parts of the home. My inspector allowed me to place one bath fan in a guest bath running at 50 cfm and another 50 cfm fan bringing in fresh air in-- in utility room. Both had single switches to turn them on or off; this simple two fan HRV(!) passed the code / inspection for Minnesota. That is not to say it works perfectly nor that I have not tweaked it. But my rationale was to save the money spent on a non-KISS HRV system to pay for the lowered efficiency of my system and LP. It has zero % heat transfer efficiency as opposed to about 65% efficiency of most HRV's so we will pay higher heating costs to account for that efficiency loss over the next years.

    -- I do not run my system 24/7 as the code "says"
    -- I watch my humidistat as a daily guide to determine best duty cycle and the fans are mostly off in spring and fall.
    -- Both fans are on timers($10/ea) to synchronize them for about 20% ON time.
    -- It would take a number of years for me to reach a break even point before my system running 24/7 cost me as much as the up front $2000 expected cost of an HRV. However, the actual duty cycle is only a fraction of the "code" requirement. Humidity concerns simply do not require it. However. . .

    I like the idea of using a combo sensor of the type suggested above($270) as a way to modulate control of these two simple fan units because only then would the real symptoms be directly addressed-- home pollutants and fresh air. That being said $270 for another device to tweak my KISS system seems offensive. . . somehow?! My whole point here is that the HRV train is way too big, far from KISS!

  14. GBA Editor
    Martin Holladay | | #14

    Response to Schreib77
    Many GBA readers agree with you on the advantages of a simple ventilation system. You have chosen to install two bath fans, one providing exhaust, and the other providing supply. If you want to simplify even further, you could have simply installed the exhaust fan without the supply fan. This type of simple ventilation system has been used for years; it's called an exhaust-only ventilation system.

    In an exhaust-only ventilation system, the makeup air enters the home through random cracks. In a very tight home, your approach -- installing a second fan -- probably makes sense, although you end up with a ventilation system that uses twice as much electricity as a traditional exhaust-only ventilation system.

    In a recent article, Revisiting Ventilation, I wrote that exhaust-only ventilation systems "are inexpensive to install and use less electricity than an HRV or ERV. An exhaust-only ventilation system can be a good solution for a small house with an open floor plan."

    The Achilles' heel of an exhaust-only ventilation system (or your variant) is that distribution of fresh air to bedrooms with closed doors isn't very good.

    In 2012, I wrote an article presenting the argument that the upcharge for an HRV (compared to a simple exhaust-only ventilation system) is hard to justify from an energy-savings perspective in all but the coldest climates. Here is a link to that article: Are HRVs Cost-Effective?

    1. schreib77 | | #35

      Yes Martin. I believe that article influenced me to do what I did. SO, thank you! The payback on a $2500 install was too long-- 6 to 10 ? years as I recall. I can still change my mind and am watching technology etc to see if an HRV comes along that is both reasonably priced(ie NOT $6000!) and incorporates CO2 and humidity either monitor or closing the loop as Andrew Bater has done(above).

  15. schreib77 | | #15

    Are HRVs Cost-Effective?
    Excellent article and review of the HRV's comparison to Exhaust only system Martin. Thanks for reference it. I read it over. However, without doing any deep research / measurement I am wary of any exhaust only system applied to extremely tight spaces. To qualify this statement it would be necessary to simply test for real air flow from one of these systems but I am reticent to believe that a 50 cfm rated fan(at zero inwg. SP resistance) connected to a closed box on its inlet side will push even 10 Acfm. In mechanical engineering jargon you are starving the pump, too low NPSH-- Net Positive Suction Head. Connecting a tight house to a fan's inlet is similar to closing off the inlet valve to a centrifugal pump. You get no flow and create a bit of low pressure at the pump eye; the pump still spins though!

    My simple system uses only low voltage DC motor driven fans at each end of the home(DeltaBreez) and allows the incoming cold air to be tempered in the utility room air around the boiler, then disperses across the entire length of the home to be exhausted by an existing, identical fan in the guest BR. We never know they are running. However, the achilles heel of my system is no closed loop control. I am planning to use a combination of a CO2 sensor and wireless relays to close this loop and have the system respond to real IAQ(CO2 level) instead of the subpar timer control. -- at the risk of losing my KISS status!

    One final point. You "have to have" clean and quality air. In your 2012 article there is discussion of the tradeoffs of doing an HRV, exhaust only, or. . . confusingly(maybe I didn't get your connection?) installing PV to offset the costs of exhausting conditioned air. It seems that is comparing apples and oranges. If you have to have IAQ, you can't trade it off for free electricity. Or did I miss something PassivHaus related?

  16. GBA Editor
    Martin Holladay | | #16

    Response to Shreib
    The article you refer to (Are HRVs Cost-Effective?) looks at whether HRVs are cost-effective (from an energy savings perspective) compared to exhaust-only ventilation systems. This cost-effectiveness analysis compared the energy savings associated with the upcharge for an HRV with the energy savings associated with a similar investment in a PV system.

    After this cost-effectiveness discussion was complete, I noted in my article that many homeowners are happy to invest in equipment that isn't particularly cost-effective because the equipment offers benefits other than energy savings -- for example, improved indoor air quality.

  17. user-6944519 | | #17

    HRV vs Exhaust-Only
    Last year I completed a Deep Energy Retrofit on my 1955 home. I considered (because my contractor friends mentioned it, often) an HRV. I decided to try the exhaust-only approach first. If it proved necessary, it would be easy enough to add a make-up air damper or an HRV later.

    Part of the DER was replacing the old single pane aluminum windows and adding 6" of polyiso insulation all the way around the exterior. As I did that, I foam and/or caulk sealed all the gaps, cracks, and holes from the foundation walls to the rafters. I taped all the plywood seams and foamed and taped all the polyiso seams. On the framed floors, I sprayed an inch of foam under the subfloor to air seal before filling the joist bays with batts. On the one ceiling I took down I filled the rafter bays with closed cell foam, air sealing them. I removed the chimney and all the combustion appliances and forced air ductwork (so...many...holes...plugged!).

    My exhaust-only ventilation system is powered by a Panasonic WhisperGreen FV-05-11 (50-80-110) in both bathrooms, a WhisperGreen FV-11-15 (110-130-150) in my basement (for humidity control and when I'm using the basement as a paint booth), and a Z Line GL14i-30 range hood (280-400-580-760). The bath fans are motion activated and remain on for 30 minutes after motion stops. One fan is set for 50cfm and the other is set for 80. With a family of four present, at least one bath fan is typically on during most waking hours. The other two fans are operated manually.

    I haven't done a blower door or even a garbage bag test but I roughly gauge the building air leakiness using a piece of yarn and a cracked window. (Fun fact, when working in a wind tunnel, we used to use yarn or dental floss to guesstimate air velocity. It takes a while for a wind tunnel to get up to speed, so watching the yarn and eyeing the gauges while working lets you get a really good sense for how the string behaves at different air speeds. Once you can guesstimate velocity, you can multiply it by area to get flow.

    With a single bath fan operating (50-80cfm), cracking a window produces negligible yarn motion. If both fans are going, there will be a slight breeze through the cracked window and the yarn will bounce around. The kitchen fan at its most commonly used 280 cfm "1" setting exceeds my "gaps and cracks" makeup air. The yarn in the cracked window will hang at an angle. We're in the habit of opening a door or window any time we use the range hood above level 1.

    The bath fans alone are almost sufficient to meet "ASHRAE 62.2 – 2010" calculated 53 cfm. While I don't have them operating continuously, their use is correlated to occupancy and they often run concurrently. They seem to run enough. If I were to drop another ceiling and air seal (and super-insulate) it, I suspect I might finally need dedicated makeup air. In that case I'd likely add a makeup air damper on a pressure switch. That's a much simpler and cheaper solution than an HRV.

  18. GBA Editor
    Martin Holladay | | #18

    More on exhaust-only ventilation systems
    Shreib raised the question: In a tight house, will a bath exhaust fan be able to find enough makeup air through random cracks to function as expected?

    Determining the answer is easy. Every bath fan needs to be commissioned. That means that you need to test the airflow rate through the fan after it is installed. If you are aiming for 50 cfm, your test will tell you if the fan is moving 50 cfm. If the fan is moving 50 cfm, it's obviously finding enough makeup air through random cracks.

    If, however, the fan is only moving 10 cfm, then either (a) the exhaust duct is convoluted and has unacceptably high static pressure, or (b) the fan is starved for makeup air.

    The bottom line: Commission your equipment! For more information on this issue, see Is Your Ventilation System Working?

  19. Jon_R | | #19

    "(PM2.5), acrolein, and
    "(PM2.5), acrolein, and formaldehyde accounted for the vast majority of DALY losses caused by IAPs considered in this analysis, with impacts on par or greater than estimates for secondhand tobacco smoke and radon."

    So I would want a sensor that measures at least these things. But no idea what I would set it at.

    I don't think that there is any problem with CO2 < 1000 ppm. But I understand using it as an approximate occupancy counter for small adjustments to airflow.

  20. Jon_R | | #20

    > They seem to run enough.>
    > They seem to run enough.
    > I watch my humidistat as a daily guide.. fans are mostly off in spring and fall.

    I can understand "enough" to manage humidity. But how does one know "enough" for PM2.5, acrolein, and formaldehyde?

    ASHRAE 62.2 isn't very scientific, but in my opinion, one should have sound reasoning before running less than 62.2 levels.

    There should probably be some adjustment for cost. Ie, it might be health neutral and cost effective to ventilate more when it's mild outside and less when it's 0F (or windy).

  21. Dirk Denzin | | #21

    We have an ERV in new home.
    We have an ERV in new home. The 3 bathrooms have exhaust fans plumbed thru the ERV. We have no exhaust fan above the range. It took us a while and several phone calls to the ERV manufacture to figure out how to run and set the ERV. The ERV initially was wired to run the furnace fan when it was running. Upon recommendation from the ERV manufacture I added a switch to turn the furnace fan interlock on or off. The ERV manufacture recommended me running the ERV continuously on with the low speed of the ERV fan only.

    After the house was finished we had an independent energy consultant come in and test the air tightness of our home. After we fixed alot of the of the sloppy work from our contractor we got the house down to 1.0ACH@50. This is on a approx 2800 sq ft house not including the basement. Interestingly enough the energy consultant recommended the we run the ERV on its most infrequent possible setting. For us that's 20 minutes of run time per hour.

    We have run the ERV non stop and we have run it on the minimum setting. We also have not run it all. We notice very little difference other than objectionable movement of air in the bathrooms and the noise. I have several humidity and temperature monitors thru out the house. Running the ERV balances the temperature and humidity better thru out the house. Especially when we close the doors on certain rooms. We find this objectionable. We prefer our bedroom to be cooler than the rest of the house. Without the ERV running a room that we close the doors on is approximately 8-10 degrees cooler than whats on the other side of the closed door.

    Another issue that is not covered is one that should not occur but does is poor equalization of the duct work. Our house has very poor equalization of the duct work. Fortunately we have a basement that allows us access to the duct work under the main floor. I already have had to fix 4 of the duct outlets. They where so poorly installed that the duct grate would not even sit down into them. Not to mention the poor sealing of the ducts themselves. At this point we have an extreme amount of air coming out of 2 ducts while the rest of the ducts have very little flow. I plan on fixing this in the near future.

    My take away from all this is aside from temperature and humidity measurements there is no way to easily monitor how much air exchange is really needed. As we sit now we don't run the ERV at all. We prefer the temperature and humidity as it works out with the ERV off completely.

    If I had to do it all over again I would insist that the duct work would of been balanced. You'd expect that would be standard operating procedure but I guess it isn't, well, for our builder it was not at least. I would also like to see a setting so that we could maybe run the ERV on a very minimal setting, maybe 5-10 minutes per hour. Another change I would of like to see was to have the ERV have its own stand alone duct work. Ducting in air out from the 3 bathrooms and air in 2 common areas. The last thing is that is over looked is explaining to the home owner how to operate the system. The manual supplied by the builder was useless. It in no way told of the functions and concept of how to run the system. ERV's are relatively new additions to houses. I'm sure that most home owners don't have this technology in their homes and consequently don't have a clue on using one and what it does.

    This is just my .02. I'm no HVAC expert or anything, just a home owner.

  22. GBA Editor
    Martin Holladay | | #22

    Response to Dirk Denzin
    Thanks for sharing your experience, which (unfortunately) is all too common.

    It sounds like your duct system was poorly installed, and your HVAC system was never commissioned to verify that the air flow from each register matches the design air flow.

    Here at GBA, we usually advise that ventilation systems should have dedicated ventilation ductwork rather than attempting to share ductwork with a heating system. It's possible that running your furnace fan is pulling in outdoor air in ways that the system wasn't designed to do.

    Finally, it sounds as if your ERV wasn't commissioned.

    I'm not sure if these articles will help you, but here's some more information on these issues:

    Residential Commissioning

    Commissioning Our Heat-Recovery Ventilator

    Is Your Ventilation System Working?

    Ducting HRVs and ERVs

  23. SwitchgrassFarmer | | #23

    Energy Efficient Homes - User Manuals?
    Martin, Dirk's comments remind me of a conversation I often have with my wife, usually after I have been engaged in some relatively dangerous activity here at the farm:

    "You know, you have never written a user manual for this house. If something happens to you it's going to take me four months to figure out how everything works here."

    "Four months" might be an exaggeration, maybe, but what kind of user manuals do Passive House, Pretty Good House, etc builders provide homeowners? I have drawers of manuals for the HRV, ground source heat pump, mix valves, thermostats etc. How does one integrate all that together into one easy to read "CliffsNotes" manual?

    Yes, I know you are going to say the house should be simple enough that it doesn't need a manual. I am a retired engineer; what fun is that?

  24. GBA Editor
    Martin Holladay | | #24

    Response to Andrew Bater
    A conscientious builder will always present a homeowner with an owner's manual or user's manual. For those of us who live in a house where the builder didn't do that, the spouse who is the "handy one" needs to prepare a manual for the other spouse. Here are a few references to this idea in past GBA articles and comments.

    In an article I wrote called "Simplicity versus Complexity":
    "It’s good for designers and builders to follow these principles: ... Provide homeowners with a three-ring binder that describes the home’s equipment and lists maintenance requirements."

    In Comment #6 on this page:
    "1. Most contractors are lax about paperwork, and fail to provide homeowners with a good three-ring binder that documents everything the homeowner needs to do to maintain their equipment.
    "2. When a house is sold, the transfer of this kind of any paperwork often gets lost in the shuffle -- especially if the house is being sold due to a divorce or mortgage default."

    In Comment #2 on this page:
    "There are lots of off-grid houses and active solar houses from the 1970s that have secret valves, secret dampers, and secret switches. The owner-builder makes all kind of seasonal adjustments, and knows exactly what to do. When the owner-builder has to go away on a business trip, he has to show his spouse a three-ring binder full of instructions."

  25. user-6944519 | | #25

    Home owners manual
    I know exactly what would happen with a home owners manual while/after I'm gone: nothing. The reason manuals don't follow the home to the next owners is because the previous owners have no idea where to find the manual(s) because they've never read or used it! Just like the manuals for their cars and their [VCR/DVD/oven/other appliance] which blinks 12:00 until someone else visits them.

    I'm all for EVERYTHING Martin recommends in "Simplicity versus Complexity" except the house manual. As a mechanical engineer by training, and a software engineer by vocation, and a writer of much documentation, I'm a real sucker for great docs. I have every manual for every appliance in my home and they're all together on my bookshelf. I'd also wager that anyone reading comments on GBA also appreciates good docs, but we should also be realists and harbor no illusions that anyone else will ever care about those manuals. So why spend time assembling a binder that nobody else will ever open?

    Instead, a single page checklist of maintenance tasks, fastened permanently to the wall or the backside of the door of the utility room has a greater likelihood of being seen regularly and acted upon.

    every time: remove lint from dryer trap
    bi-monthly: remove, rinse, and replace water heater air filter
    bi-monthly: make sure no error lights on water heater
    annually: pour a 5-gallon bucket of water into the sump bucket and watch it get pumped out
    January: rotate mattresses 180°
    July: rotate mattresses 180°
    August: rinse and replace air filters for 2 upstairs heat pump heads
    December: rinse and replace air filters for 2 downstairs heat pump heads

  26. Expert Member
    MALCOLM TAYLOR | | #26

    That's a very good point. I've struggled with the idea of owners manuals for the houses I've built. One real concern is liability, both in what you choose to include, and what you might omit.

    Having permanent signs near equipment with simple instructions makes sense to me. Leaving all instruction manuals or those who chose to use them seems like a good idea too.

    I don't think I'd ever venture outside of basic instructions for the building enclosure and systems. If people don't know to clean their gutters or dryer trap, well...

  27. john_prospect | | #27

    Certified Products Directory
    I found the certified products directory very interesting. Following the article advice, and sorting by SRE on HRVs, there are only the Zehnder, the new Venmar X24 series, and a Reversomatic I have not heard of, that come above a SRE of 80%.

    The Venmar E15 ECM (which used to be the EKO 1.5 HRV) was a suggested pick for energy use in some previous articles, but only has a SRE of 75%. Has anyone used the new X24 ECM units? They also seem to provide more air flow.


    Edit: In the directory, I believe the vanEE and Broan models at 81% are re-branded Venmar units.

  28. GBA Editor
    Martin Holladay | | #28

    More on homeowner's manuals
    I'm attending a building conference in Burlington, Vermont. Yesterday I attending a presentation by Matt Sargent from Efficiency Vermont. He reported the results of in-depth interviews with 11 homeowners, all of whom had built a new custom home enrolled in Efficiency Vermont's "high-performance home" program. (Basically, Efficiency Vermont is promoting pretty good homes with thermal envelopes that have high enough specs to allow the homes to be heated with ductless minisplits.)

    Among the themes identified by Matt Sargent were these: "It was really hard to find an experienced contractor" and "I wish we had a homeowner's manual."

    Recurrent questions that the homeowners mentioned -- questions that could have been addressed in a good homeowner's manual -- were "How do we operate the ventilation system?" and "How do we operate the ductless minisplits?"

  29. Brian Knight | | #29

    Homeowners Manuel
    Something we are adding to add to our homeowners manuals related to HRV/ERV is a picture of exterior outlet and inlet with comment to inspect regularly and keep screens here clean.

    I also think it's very helpful to include pictures of underground utilities location, including downspout drain pipes and outlets.

  30. SwitchgrassFarmer | | #30

    You have to clean the HRV screen?
    Yea, this is on my list of things to re-engineer. These screens are problematic.

    My goal will be to capture more dirt outside, with some sort of filter, before that accumulates as "micro-dirt" on the HRV fans, filters, and core.

    I am dreaming of some sort of Fram/Fleetguard/etc truck engine air filter contraption, or maybe even a centrifugal dust bowl pre-filter like the one on my John Deere bulldozer. (My other dozer has an oil bath air filter; somehow I think that is a bad idea for a home.)

    1. NetzeroinNH | | #36

      Hello Andrew - I am concerned about the level of filtration on the core filters. We have two HRV systems, one being for an apartment, that work in coordination with our ducted mini-splits. We have very good return and AHU filtration (up to Merv 13) on our conditioning systems. Our two Broan HRV systems have either a simple foam filter (small one HRV80S) or a more elaborate fiber mat/plastic screen for the larger whole house model. The larger filter sandwich seems to do a good job as I clean it each month and it is loaded with dust and particles. I am concerned about the foam filter and I am looking for a replacement that will improve the particulate retention while not offering a drastic pressure drop. Sending this out in case any person can offer research or resource sites. Thanks

  31. RMaglad | | #31

    ERV Controls
    Is anyone aware of a control that "links" the recirculating range hood with the ERV boost mode? Whereby when the range hood fan is turned on, the ERV automatically goes into boost mode without having to go hit another switch?

  32. CramerSilkworth | | #32

    ERV Controls
    @Ryan: A current sensing relay is what you need - you run the power line to the hood through it, then when it senses current flowing, it closes the relay contact. If your ERV has a "dry contact" connection for boost mode (Zehnders do, and I think some others) this should do the trick.

    There are various types, you just need to check their amp ratings, but this one should work:

    If the hood doesn't draw enough power to trigger it, you can loop the wire through it a few times to multiply its sensitivity.

  33. user_8675309 | | #33

    The best laid plans...
    Just took a tour of new homes in the Anchorage, Alaska area yesterday. Out of 6 or so homes visited, only one had an hrv and that one had fresh air venting into the bathrooms and stale air exhausting from the bedrooms. Also no insulation on the ducts going to and leaving the unit. Sigh.....

  34. Deleted | | #37


  35. drafthunter | | #38

    ERV retrofit in existing homes

    I have scoured through tons of articles regarding HRV’s and ERV’s on this site. Not one adequately addresses installing an independent system in an existing house. Every article takes the easy way out of just posting an idealistic rendered diagram that only addresses new construction.

    Instead, why not have real world examples on what it really takes to install one yourself?

    In my case, my biggest concern is where to buy continuous rigid flexible duct and manifolds like this:

    Zhender is the only one, but there prices are astronomical and I’m not sure if you can just buy the ductwork and retrofit with other ERV’s

    Next would be, since it needs to be in conditioned space, getting ducts to bedrooms is very difficult since you can’t go through the attic. Are there workarounds that would let you through an unconditioned attic? I have fiberglass batts and blown cellulose for R48. Would running the ducts under the insulation be sufficient?

    If you can’t get to every individually, what are some workarounds?

    What would be the best guidance in drilling holes through sill plates, blocking, floor plates to get from floor to floor etc? None of this is covered anywhere I’ve looked.

    Even trying to find someone who will professionally install them has been next to impossible. Panasonic and Fantech for example list supply houses as their dealers. Not one installer is listed for either of them. Very frustrating.

    I’m hoping one of the experts here will chime in.

    Lastly, it’s very concerning that homeowners here think an ERV/HRV’s sole purpose is humidity control and have in fact decided to shut them off. Or that someone thinks that exhaust only was enough and then doesn’t even run it.

    Not one expert chimed in to correct them! Adequate O2, excessive CO2 VOC’s and Radon are the most pertinent reasons for a ventilation system. This was well known back in 2018 when these posts wee made, but now during the pandemic with more and more people stuck in their homes 24/7, is blatantly obvious.

    1. Expert Member
      MALCOLM TAYLOR | | #39


      I'll take a stab at bits of this and leave the rest to others with more direct experience. The ease of retrofitting mechanical ventilation probably varies too much to make any blanket statements about. A bungalow with a conditioned crawlspace being one end of the spectrum, a multi-story townhouse with cathedral ceilings perhaps representing the other. My feeling is for the complex ones spot ERVs are probably the way to go.

      Your suspicions about homeowners and mechanical ventilation are borne out by my experience here in BC. Once the code mandated that they be included in all new construction, I soon heard anecdotal evidence from the builders I know that homeowners were turning them off, without understanding the implications of doing so. That seems to come directly from them not knowing why they were there in the first place. Those fault that is I can't say.

      1. drafthunter | | #42

        I very well may have to do spot ERV’s. My concern is if I add one like the Panasonic WhisperComfort, on the second floor, the wall cap would be right underneath the soffit vent. What’s the best way of preventing moisture from going into the attic?

        I saw someone suggest taping over the soffit holes. How much would you have to tape? I don’t know if there are other suggestions?

    2. charlie_sullivan | | #40

      Maybe if you tell us you location some people can help you find installers.

      Yes, Zehnder sells ducts, etc., separately from the system. I happen to have a bunch of extra in my shed that I'll sell you very inexpensively if you are close enough to me (central NH/VT) to make it worth the trip.

      In my install, we mostly found ways to run them in conditioned space. One set had to go through the garage so we made a soffit, very well insulated, and boxed in with 5/8 drywall for fire protection, carefully air sealed. It was a pain, it was expensive, but it's a great system.

      If we hadn't wanted filtration on the input, I might have gone with a ductless system like Lunos.

  36. drafthunter | | #41

    Hi Charlie,

    I live in Nassau County Long Island, NY. Way too far for me, but thanks for the offer. I’ve seen other tubing systems used that are similar to Zhender’s, but can’t seem to find any available in the US.

    At what point do you have to be concerned about drilling a 3” hole in sill plates etc. to go from floor to floor?

    Recommended installers would be great. I found only one, and had really bad reviews on Yelp and Angie’s list.

    I’m even considering a CERV but I’m concerned with maintenance or warranty of an item that only one small manufacturer makes. It’s also not clear who installs them.

  37. wolfnowl | | #43

    Under 2. above, the link to the HVI's Certified Products Directory leads to a file not found error. This link works:


  38. orilev | | #44

    If creating a dedicated duct system (#5 above), how cool/warm is the incoming air and is that a problem? I know that the ERV transfers heat from/to the exhaust air, so that the incoming air is warm in winter and cooler in summer than the outdoor air, but I assume it's not as warm or cool as the indoor conditioned air. Is having a dedicated vent blowing cooler/warmer air noticable or a problem? I'm trying to decide between dedicated duct system and using the existing HVAC ducts. Thanks.

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