Using an Energy Recovery Ventilator In Lieu of Exhaust Fans In Bathroom

By Duane Amundson

Energy Recovery Ventilator. Photo courtesy of RenewAire

My home in Wisconsin was well built in 1966, with extra insulation and good air sealing, attributes which have only recently become common in today’s energy conscious homes.  What it did not have was adequate ventilation given its tight envelope.   We found a solution for this problem by installing an Energy Recovery Ventilator (ERV).

We moved into the home in 1996.  During that first summer, with air conditioning operating for several days, I noticed the house had a stale odor to it. I attributed this to the fact that the windows had been closed, and we were just cooling and breathing the same air every day.  Some time later, we decided to install an ERV with hopes of improving the indoor air quality (IAQ).  We were glad we did.

What is ERV Technology?

An ERV exhausts stale air with its fan, and brings the same volume of fresh air back in.  A built-in heat exchanger allows the fresh air to be semi-conditioned by the exhaust air, so that you aren’t just tossing out air you’ve already paid to heat or cool. A master control timer runs the ERV fan from 6-60 minutes every hour to manage how much fresh air is introduced, based on the amount of activity or number of people in the home.

Following the ERV installation in my home, I also began investigating options for solving some bathroom ventilation issues we were having.  Specifically, the bath fans were noisy and did not do a good job removing odors or humidity.  The white ceiling above the shower was developing black and gray patches due to mold and mildew.  At least twice a year, I had to carefully maneuver a ladder into the shower to reach the 8-foot ceiling in order to scrub it down with bleach.  In between cleanings, the stains were embarrassing when guests came to visit.

The Problem with Bath Fans….

Manual on/off control of bath fans was part of the problem.   One of two things always happen with this type of control.  You either turn the fan off upon leaving the bathroom which isn’t a long enough run time, or you end up leaving it to run all day, which wastes energy.  To solve this problem, I installed a timer wall switch that would operate the fan for a set period after it was turned on.

But this didn’t solve all of our problems.  For one thing the bathroom fans vented directly into the attic, a common practice years ago, but one that is forbidden by most current building codes today because of associated moisture problems.   I also wasn’t crazy about exhausting all that heated or cooled air from the living space every time we turned on a fan.  So, I began to investigate ways to connect the bathrooms and the even the kitchen area to my ERV.  That way we would be extracting some of the energy from the exhausted air to temper the fresh air being introduced into my home via the ERV.

ERV Does All the Work

With the help of an HVAC technician, ductwork from these areas was routed back to the ERV.   I actually removed the inner workings of the bathroom fans, leaving that space free of obstructions to airflow, so that the ERV could pull air from the bathroom when we operated the timed switch.  As a result, the measured airflow from the bathrooms nearly doubled that of the previous bath fans, and both bathroom and kitchen odors have been noticeably reduced.

More Energy Efficient Home Ventilation

For the past three years, I have activated my ERV daily with the timed bathroom switch for 20 minutes in the morning for showering, while the master ERV control automatically provides additional ventilation every hour.  In terms of every day living, this change has resulted in my no longer having to clean the shower ceiling and the elimination lingering kitchen odors—even after a stir fry meal. And we don’t have to operate the loud kitchen fan as often as before.

I’m also not throwing away air that I have already heated or cooled just to ventilate the bathrooms and kitchen area, and the ERV is saving me energy (and money) that was previously wasted.  Moisture isn’t being blown into the attic, and I no longer have to listen to the irritating drone of the bath fan when I am in the bathroom.  My house is now a quieter, more energy efficient place to live.

Duane Amundson lives in Prairie du Sac, Wisconsin and has worked as an energy saving consultant for the past 10 years.  He has incorporated many energy saving features to his own home, including CFL bulbs, ceiling fans, a more energy efficient light colored shingles, and an air source heat pump and a closed combustion gas fireplace insert.  Plus, all his family vehicles are now hybrids. His other “green” claim to fame is that he was the very first Campus Recycling Coordinator at University of Wisconsin-La Crosse, when he was a freshman in 1973.


20 Responses »

  1. I’ve been wanting to do some research on EVRs and thoroughly enjoyed this story. It was nice to read about a new, green home product … from the homeowner perspective. Much more interesting

  2. How are ERVs sized? cfm, hp? What size is typically required for, say, a 2000sf home? What are typical price ranges for residential grade ERVs? Do you recall how many hours of labor was required for the each of the elements? I know I could call up a local HVAC company, but then I’d be likely to have to endure a sales pitch. You’ve already been down this road, so I figured you might have the info readily at hand.

  3. [Brand name withheld] ERV’s are sized by CFM & how much is needed is calculated using ASHRAE 62.2 which uses a simple formula (# of bedrooms +1 X 7.5) + (1 CFM per 100 SF) = CFM needed so for a 3 bedroom 2000 SF house it would be 50 CFM (3+1 = 4 x 7.5 = 30 + 2000 / 100 = 20 —- 30 +20 = 50)

    Now there are other factors like existing leakage, exhaust fans, etc… which can lower that number but when designing new we prefer to ignore those other numbers for sizing & instead install an ERV that is closest to that while watching the watts per CFM. Because of those other numbers we ignored earlier we do reduce how often the ERV runs (which is overkill for most people anyways – unless they smoke indoors, have a ton of plants, or animals) & have it run only 25 to 50% of the time required when people will be home.

    Prices vary & a lot depends on your house & how complicated it is to install one, but the best method is as a standalone & not connected to the HVAC system (though in most states a licensed HVAC technician is required). I would also generally recommend staying away from using it as an exhaust system for steam & cooking as an ERV has a filter which can get clogged & soaked by those containiments. It might work great for some, but can be a disaster for others. It is best to make sure you use the regular exhaust fans as they are met to be used & make sure they are vented outdoors away from the ERV or other intake.

  4. I was asked to comment.

    My feelings on this, the unit is founded on good principals. The commercial/industrial HVAC industry has used heat recovery for a long time, but commercial HVAC has some advantages such as a dedicated workforce to maintain things when stuff doesn’t work as expected and usually (somewhat) expensive digital control systems that provide the feedback to operators who should be able to quickly diagnose problems. The size of commercial/industrial systems justifies the use of heat recovery.

    The value of heat recovery for “tight” homes in inclement weather regions – where heating or cooling is very expensive is likely a good idea. from appearances the unit has two fans, an intake and exhaust fan. The intake fan should be slightly larger than the exhaust fan in that, if properly installed, there should be an outside air intake with a filter on it. The larger intake fan overcomes the pressure drop from the in-line outside air filter. In freezing weather, I’d be concerned that the configuration of the intake, and exhaust for that matter, would be a “thermal hole” in the building envelope allowing freezing to occur inside the home. Commercial/Industrial systems have more components including variable outside air dampers, temperature and humidity sensors that warn the main HVAC systems to reduce outside air off should the system approach freezing conditions.

    For a home’s main air conditioner/heater the system makes sense. When the AC turns on, this heat recovery unit can run.

    For bathrooms fan exhausts, it seems this would be an expensive solution.

    First, instead of running one fan motor, you’re running two, or you’re running a larger fan motor with a long shaft running two fans (more likely), so from an energy perspective, it may depend on the season. If it is a hot an humid summer and the incoming air is brought into the home, some condensation should occur in the heat exchanger, reqiring a drain and causing some corrosion or fouling, increasing the need for maintenance. If during a cold winter and the use of a shower in the bathroom, the same might occur. (It really depends on the change in temperature and the humidity content of the two airstreams.

    It would be nice if home units were more simply designed with the ability to modulate between outside and return air. It would also be nice if home units used modulating heating water or cooling water in the AC unit rather than the On/Off of refrigerant based evaporator/condenser spit-systems (straight AC or Heat-pumps) or On/Off gas heating systems.

    With today’s mass production techniques, with the advent of so many home consumers being quite computer literate and mini control systems being so common, and with the low cost of “variable speed drives”, it is very much a shame the home AC market has ignored the “custom-ability” of home systems to suit the peculiar conditions inside a home.

    It’s probably not worth having an HVAC engineer run all the calcs and produce all the sequences of control and install controls to integrate a home heat recovery system to consider the operation of bathroom exhaust fans into a home HVAC system. My hunch is that installing heat recovery on bathroom exhaust is going overboard.

    But each circumstance is different. Each homeowner has different incomes and different limitations on what they are willing to spend on “reducing stink”.

    In regions where temperature extremes are common most of the year, the very cold north and the very hot and humid south, the homeowner may just want it. Out here in temperate coastal California with leaky houses built in the fifties, sixties and seventies, we shouldn’t take the time.

    In Wisconsin or Florida where “tight” might be extremely tight, such a fan may be a viable solution to a problem they can’t get rid of, a stinky bathroom.

    • My ERV and controls are very simple. (These have been around for over 30 years; primarily starting in the home market during the 70s energy crisis, and moved into commercial.) It automatically operates with the master control, based on my desired air exchange rate, and on demand like a bath fan. It is not dependent on how hot or cold it is outside, or whenever the heat or A/C comes on, which would be counterproductive. The system is a two in one; a whole house exchanger, normally required in a tight home anyway, along with the added benefit of replacing the bath fans and providing added kitchen exhaust. Why not use something you are going to buy anyway, do two things instead of one? You do not need bath fans if the ERV and ductwork are sized correctly. Some fans are quiet and energy efficient, but are still pumping air out of the house that you have already heated or cooled, so that energy is wasted when that air leaves the house. The unit does not have a drain and has not produced condensate (many do however) in 9 years. These units have filters to protect the exchange core. Mechanical backdraft dampers could be installed to shut off outside air whenever the ERV is off.

      Municipalities and states are increasingly requiring a sizing calculation for each home, whenever installing or replacing HVAC systems, and are commonly done by good quality HVAC contractors, even regardless of code requirments. Several industry organizations and manufacturers promote HVAC technician training, to get the most out of the homeowner’s energy dollar. I interviewed 3 companies when I replaced my HVAC system (with a two stage heating and cooling and variable speed drive; more costly) and had my house tested for proper HVAC sizing. Energy recovery of bath exhaust is going overboard only if the house tightness, insulation, and lack of air sealing does not warrant an ERV to begin with. For those energy concious like me, we invest in the upfront costs to save in the long run. Others just get the cheapest things and pay more every year. Energy costs are not going down folks.

      • We utilize an ERV in our home built in 2008 near Des Moines, Iowa. Our 2000 square foot ranch has an insulated concrete form finished basement and upstairs are 2X6 walls of high dense pack cellulose, and three pain windows. The energy company testing indicated a 1.12 natural exchange rate given its tightness. I have no complaints accept that I notice the bathroom odor does not leave as fast as it should, unless I open a door somewhere in the home eliminating the negative pressure that bathroom fans cause (yes, its that tight) I am very pleased to read your letter about using the bathroom fan ducting and attaching them to the ERV. I’ve been racking my brain to come up with a solution and you have it. I just need now to route my flexible insulated fan ducting from my attic through the house and into the ERV rather than using the cold air return from our HVAC system. Issue nearly solved, just need to take the time now and do it. Thank you!

  5. Very nice device.

  6. Hi Trish,
    Thanks for your request to reply about ERV’s in residential construction. I am an architectural designer and general contractor and have encouraged ALL of my clients to install this system.

    I am an avid believer in the use of ERV’s and when I built my house in 2000 I had two installed. They were connected to the bathrooms so that when you wanted to activate the units, you would push a button that would be on a timer for 20 minutes and up to 60 minutes depending on how long you wanted it to stay on. You can also install switches that are motion detectors that activate when you come into your bath.

    The ERV allows you to evacuate the baths, in that it exhaust the room in running that already conditioned air through a “radiator” type device in the unit, sending it directly to the exterior and at the same time, bringing in fresh exterior air back through the “radiator” and sends the fresh air to the return air. It is my understanding that it recaptures 80% of the already conditioned air that you’ve paid for.

    With houses being built so much tighter with better insulation and better windows and doors, it is imperative to bring in fresh air in lieu of depending on that fresh air coming in when you open your doors. In our area, it is best not to open your windows, due to all of our allergens and pollen that can be trapped in your home. The ERV allows a safe exchange of air that is filtered.

    With the use of the [brand name withheld] type filers in the return air, this system gives you piece of mind that your home is not toxic and stale. The typical exhaust fan just evacuates the room without any consideration of the air that you have paid to condition.

    Thanks for allowing me to provide my opinion.
    Larry McRae

  7. Most every home would improve the IAQ, by installing an ERV. Using one as the bath(s) exhaust is a very good idea. That said you could get fresh air by opening a window, ERV is more energy efficent, but there is a cost for operation and maintenance.

    One possible issue when used as a bath exhaust is the “exchange” of air is now humid air from the bath ,at times. However that air has to be dealt with some how. In a humid climate, whole house dehumidifier may be required.

  8. This is a very complicated issue and should really be evaluated by a professional building envelope scientist in order to reap the benefits of the system. YES a scientist! I have had one of these systems installed in the past and it can become quite daunting to install properly. The owner did not heed my advice to spend the extra dollars in having the system engineered properly and opted for a standard HVAC contractor to install the system. Ultimately he was not satisfied with the system. He got what he paid for!
    You have all been talking about an ERV, Energy Recovery Ventilator, which mixes some of the outgoing air with some of the incoming air as a way to exchange moisture. Removing a small amount of humidity in the summer and adding some in the winter. Some of the stale air comes back into the house. (10%) There is also an HRV, Heat Recovery Ventilator, which utilizes the out going hot or cool air to temper the incoming air without mixing the old with the new.
    If you have forced air heating and ventilation the incoming air enters the return duct of the heating/cooling system when the ever the system comes on. That way the incoming fresh air ,lets say 90 degrees, will be slightly cooled by the exhaust air pulled from the ERV or HRV before it enters the air condidtioner so it only has to cool 80 degree air instead of 90 degree air.
    There are other controls that can be added such as humidistats at bathrooms so the system starts and stops based upon the relative humidity of the room. CO2 detectors can act as a relay to exhaust stale air when reaching programmed levels.
    Please copy and paste the link below to refer to an article reinforcing how important it is to hire the right scientist for the job.

    • HRVs transfer heat; ERVs transfer heat and humidity. ERVs do not mix the two airstreams, but utilize different technologies to transfer moisture between airstreams. Most (not all) HRVs and ERVs are voluntarily rated (they pay to be tested) by HVI (Home Ventilating Institute), the only independent rating agency for air exchangers. One of the tests is exhaust air transfer ratio (EATR), which varies from 2-10% for all units. Heat transfer efficiencies vary from @ 55-85% and moisture tranfer 0-65%. If a company doesn’t think it’s a good idea to pay for the independent testing, I won’t buy it. Test results are on the HVI site; Untested units only have colorful brochures. Look for a good quality, reputable installer, who should know about simple duct sizing. I ran some of my own ductwork and got the results I intended; not real hard stuff. Use HVI Certified products, installed how (and where) the manufacturer of that product intended it. Products vary by capacity, quality, results, maintenance, and intent of use.

  9. ERV’s are essential to homes with foam insulation. Without them a home with “tight” insulation will disintegrate into a mass of mushy mold, mildew, disease and eventual condemnation. Wood is food. Moisture = death. Where’s the debate?
    Dan K.

  10. It’s a timely question. We have installed HRVs in our newly renovated building in downtown Durham (, I recently installed an ERV in my 1200 sqft. 1940 brick bungalow, we used two for completely different reasons on an energy retrofit job we did recently, and we’re in the process of energy model comparisons for a new design-build project in nearby Raleigh in which the xRV vs. bath exhaust timers plays on the main stage.

    I have to say I was a bit surprised by the official data in our energy modeling exercise for the house in Raleigh. In our mixed climate, the numbers come back at just about a wash. Feeling a bit defensive, and armed with information from an EEBA ventilation seminar I attended last year which basically came down to a question of which RV to use (not whether or not to use one), I pushed back a bit with our energy modeler (a reputable, widely respected area firm), and he confirmed that he had all his bases covered. All things considered (ventilation needs and energy cost), the ERV is projected to cost $3 more per year to operate than timed bath exhaust fans with passive inlet. Having spent $2400 on my ERV install, I had to sulk a bit about the payback!…until I realized that payback is not the only factor in my decision-making. Or actually not at all.

    I’ll do some things a little differently next time, but here are the benefits that we get by going with an ERV as opposed to the bath exhaust route. I have seven ducts on my ERV. Three are returns and four supplies. The three returns draw air from our two bathrooms and from the dining room (just around the corner from the stove in the kitchen, so not a direct smoke sucker). I did not have to put a dedicated exhaust fan in our new second bathroom because the ERV return was sufficient. While we have some work to do to keep our dishes from piling up and diapers and such, adding odor to the space, the ERV made an immediate impact with a fresh air smell and feel when I walked in the door at the end of the day it was installed. And while bath exhaust draws “fresh” air somewhat willy-nilly from cracks and crevices in walls, floors and ceilings, if not from a passive inlet, I get to direct filtered fresh air exactly where I want it. The four supplies are in each of our three bedrooms and in the family/living room. I could be mistaken (in other words, I did not gather family data), but over the last 10 months we’ve had the ERV, I think we’ve all been sleeping better. It’s hard to put a price tag on that.

    Now, I have some modification to do. I don’t have a control module, like a switch or thermostat on the wall for the ERV. There several options, and I will put one in soon. Right now, I run it at low speed continuously, which is about 70 cfm. With the five people in our house, that’s pretty close to ASHRAE 62.2 minimum of 75 cfm. (With our fourth child coming soon, I guess I ought to bump up the speed!) High speed is around 100 cfm. I’m not really sure about the energy use of the different speeds, but I wonder if I would use high speed intermittently, if it would save some watt usage over continuous low-speed operation. I have a notion (I have not had corroborated by any expert) that the balanced nature of an ERV discourages air leakage in a house, too. Maybe some of you can comment on that.

    I don’t know where some folks come up with ERV/HRV install prices. It seems like they are a whole lot cheaper to install up north. One way to save some money on an install is to do it yourself. It’s my understanding that because it does not involve coolant or heating fuel, I do not need a certified HVAC installer to do the work (it’s basically a glorified fan in a box). I’m not sure if ERV/HRV use is increasing in our area, but I would hope the price would come down in the coming years as volume increases.

    Daniel, you’re right about the three m’s (moisture, mold, mildew), but ERVs are not the only way to address those in a foam insulated house. They are a good one, and maybe the best and most versatile, but not only.

  11. Duane Amundson – Yes, the ON/OFF control of such a unit is very simple for a whole house situation, even if the unit turns ON from relays run off bathroom fans.

    But programmed digital controls with user interfaces displaying live flow-chart programming are often actually simpler to install and diagnose than other control systems. These are predominantly used in commercial/industrial situations due to their high cost. Combined with variable speed drives, modulating cooling and heating coils and modulating Outside/Return Air Dampers can significantly improve the energy performance of any building.

    For example, you may have an ERV of 500 CFM that runs with your AC/Heater. But your bathroom fan is only drawing 100 CFM. If it were cost effective to control a home AC/Heater with Direct Digital Controls as it is in commercial situations, you could actually run the whole AC/Heating system at 100 CFM when someone is using the bathroom.

    A building complex I worked on in Orlando required that the exhaust system (and supply air system) run continuously to prevent the inside of the building from suffering mold damage. Using DDC, it was not hard to set the supply system to 20% and lock all the (700) zone controls – except the bathrooms – to minimum air flow after hours.

    Again, too bad home HVAC hasn’t gotten anywhere near as effective as commercial HVAC. Cisco bought Richards/Zeta for the interesting networking capabilities, but let the product line die on the vine. They were pretty easy to learn and Cisco kind-of blew it by not figuring out they could have marketed them to home automation enthusiasts.

  12. ERVs and HRVs do make sense as substitutes for bath exhaust fans. We did just that in small affordable houses in our Santa Fe market that were built in 2008. To make sure they worked as whole-house venilation systems, we installed jumper ducts in both bathrooms and laundry rooms and made sure all bedrooms had jumper ducts as well. If bathroom and laundry rooms doors are kept shut and there are no jumper ducts, then the effectiveness of the HRvs is significantly hampered by restricted air flow.

  13. H/ERV’s are essential for “tight” buildings and exhausting the bathrooms and kitchens is a good way to reduce pollutants and humidity in the structure. In addition, by leveraging the ERV in the baths and kitchens, you can reduce the number of penetrations in the building envelop (e.g. fewer exhaust vents to the outside). Those penetrations are generally a tremendous source of heat loss in the winter.

    The only issue I have found is kitchens with commercial exhaust fan needs. Residential H/ERV’s are not designed to exhaust huge volumes of air.

    Also, if your home is not super tight, you can still benefit from an H/ERV. They generally have good filtration capabilities. For example, the UltimateAir product has a MERV 12 filtration rating. For people with allergies, asthma or other respiratory conditions, the better air quality will help alleviate the related symptoms. Some manufacturers have mentioned a potential benefit for radon dilution. However, none have been approved as a radon mitigation option as far as I know.

    Larry mentioned above that 80% of the heat is captured and there are systems out there that do better than that.

    Someone else mentioned other options like CO2 monitors that boost CFM and another option is positive pressure to provide “extra” air for natural gas combustion products like furnaces and water heaters. Positive pressure helps to insure the water heater and furnace CO2 goes out through the vent and not back into the building.

    Finally, nobody mentioned the need for freeze protection. Some H/ERV’s have built in freeze protection as the heat exchange core can freeze at cold outdoor temperatures. Some have a mechanism that just recirculates air but does not bring in fresh when the outside temps get super cold. Others have anti-freeze options that warm the incoming air so that you always have fresh air coming into the building.

    Great discussion.


    Todd Collins

  14. I have an ERV which supplies its fresh air to my furnace return air drop.
    If i don’t turn on the furnace fan blower at the same time i am running the ERV. It will blow the fresh air backwards through the cold air return vents.
    Im looking at getting it wired to the furnace correctly so this will be automatic.

    Long story short.
    What i learned about having an ERV.
    We dislike running it while outdoor RH is higher than indoor RH. I wish there was a sensor for this.
    My wife will run the ERV after a long shower without checking outdoor and indoor RH first.
    It could be 39% RH in house and outside is 65%.
    Within minutes the inside of the house is at 65%.

    I hate how the ERV lets outdoor humidity inside the house.
    I hate how the combustion air vent in my basement poors freezing below zero outside air all night and day in the winter. I want to move into a different structure.

  15. P.s I didn’t see it mentioned yet in this forum thread but Keep in mind that when you run ERV to bathroom.

    It is best to have bathroom vent connected downstream from kitchen or vaulted ceiling vent.
    Bathroom connection should be connected on a metal “T” ( tin boot) with red tape closest to the ERV than other boots. Less chance of airborne issues we have determined.

  16. We live in a new passive energy house in the deep south…lot’s of heat and humidity and mild winters. It’s not certified passive due to size (6,800sf) and window area, but otherwise it exceeds passive standards. We use a (brand name withheld) ERV in conjunction with a (brand name withheld) HVAC system. The system makes economic sense for us and delivers comfort we desire. The system architect did a good job by venting through the bathrooms so these do not add expense since they double as both bathroom exhaust and ERV vents. With 7 HVAC zones and 3 ERV zones, the ERV units each pull from more than one bathroom and 2 other (non-bathroom) vents.

    Cons: while we managed expenses (and construction energy waste) by integrating the ERV and HVAC, we have paid a price in air quality since air is forced back out the HVAC return air vents when the ERV runs and the HVAC does not (since they share exhaust vents). Our intake grills house air filters so collected dust is effectively blown back into the sealed living space as residual ERV air blows out of the HVAC exhaust vent.

    Recommendation: hire a system architect that works with the HVAC installer. In our case, the installer did not really understand the system design and the system architect did not consider some important installation issues. Moreover, (brand name withheld) engineers do not address (brand name withheld) issues and vie versa. This became a problem with an integrated system design…in short, everyone gets paid but no one takes full responsibility nor is anyone completely knowledgable or accountable.

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