Air Exchanger Cleaning in Minnesota: The Part People Forget
Your air exchanger is the third air system in your house, after heating and cooling, and it is the only one nobody has ever told you to maintain. In most Minnesota homes built in the last decade there is an HRV or ERV hanging in the mechanical room, code-required, running year round, and still wearing the filters it left the factory with. Two filter checks a year and a periodic deeper clean is all it asks.
Here is what it does, why the code made it standard, and what actually needs attention.
What the box in the mechanical room is doing
The Minnesota Department of Commerce puts the purpose in one line: air exchangers provide fresh air for occupants that used to be provided by leaky houses, before we insulated and sealed them properly. Tight construction is a good thing for energy, but it removes the accidental ventilation that old drafty houses had. Commerce is specific about what accumulates without a replacement: an unhealthy build-up of odors, carbon dioxide, or volatile organic compounds.
There are two versions, and they are not interchangeable:
- HRV, heat recovery ventilator. Exhausts inside air, brings in outdoor air, and captures heat from the outgoing stream to preheat the incoming stream. The two air flows do not mix.
- ERV, energy recovery ventilator. Does everything an HRV does and also transfers moisture, moving humidity from the exhaust air into the incoming air in winter and restricting incoming moisture in summer.
Opening a window does the same job at considerable energy loss. That is the trade the equipment exists to solve.
Minnesota does not treat this as optional
This is the part most homeowners do not know. Minnesota Rules 1322.0403, the residential energy code, states that the building shall be provided with a balanced mechanical ventilation system that is within 10 percent of the system’s design capacity. Balanced means what it sounds like: the air coming in has to be within 10 percent of the air going out.
The code goes further than requiring the box. It sets the delivered rate. The total ventilation rate is calculated as 0.02 cfm per square foot of conditioned space plus 15 cfm times the number of bedrooms plus one, and the continuous rate has to be at least half of that and never below 40 cfm. For a 2,400 square foot, four bedroom Woodbury house, that is a real number the system is expected to hit continuously.
It also anticipates our winters directly. An HRV or ERV has to meet HVI Standard 920, a 72 hour cold weather test at minus 13 degrees Fahrenheit, or be certified by a registered professional engineer. And for systems moving more than 30 cfm, the airflow has to be tested and verified at the time of installation.
Two things follow from that. First, the code cares about air actually delivered, not equipment installed, and a loaded filter or a blocked exterior hood is the difference between the two. Second, alterations to existing buildings are exempt, so an older East Metro home may have no exchanger at all, and if someone added one it may never have been balanced.
What actually needs cleaning
Filters, twice a year. The Minnesota Department of Commerce guidance is to clean or replace HRV and ERV filters in the spring and the fall. Most units have two, one on each air stream, behind a door you can open without tools. This is the single highest-value maintenance task in the whole system and it takes ten minutes.
Exterior hoods, after every heavy snow. Commerce specifically calls for checking exterior vent openings for blockages from snow, debris, or insects. In Minnesota this is not a footnote. A drift against the north wall, a wasp nest in the intake, or a hood buried by a plow blocks ventilation completely, and the unit will keep running against it without complaint.
The heat exchange core. Air passes through a dense passageway on both sides, and dust accumulates in it. A dirty core loses heat recovery efficiency and restricts airflow. This comes out for cleaning per the manufacturer’s instructions and is not a twice-a-year job, but it is not a never job either.
The ductwork on both sides. The intake and exhaust runs and any distribution ducting are collecting the same dust as the rest of the system, which is why the exchanger is worth doing at the same time as a whole-house cleaning rather than on its own trip.
The condensate drain. HRVs produce condensate in winter. If the drain or trap is plugged, water backs up into the unit.
The Minnesota timing that matters
Do the filters and the core before heating season, not during it. From roughly November through April the exchanger is working hardest, the exterior hoods are exposed to snow, and the house is closed up tight. Going into that stretch with clean filters and clear hoods is the difference between a system that quietly does its job and one that is running at half its rated airflow while the windows fog.
If your house is a newer build in Woodbury or Cottage Grove, you almost certainly have one. If you are not sure whether yours has ever been serviced, look at the filters. That answers it in under a minute.
Booking it
Fresh Air Vents cleans air ducts and dryer vents across the East Metro with truck-mounted, 7,000 CFM equipment, and Adam does the work himself. Air exchangers are a separate scope from a standard duct cleaning, so we quote them separately and tell you the full number up front. Pricing is posted on our pricing page, and the signs worth watching for are on our air duct cleaning page.
If there is a box in your mechanical room with a fan you have never turned off and a filter you have never opened, that is the one. Book at book.abcamservices.com or call 651-425-1678.
Adam Bonine
Owner of Fresh Air Vents, serving the Twin Cities East Metro since 2006. IICRC certified and fully insured.
What is an air exchanger, and why does my Minnesota house have one?
An air exchanger, usually an HRV or ERV, exhausts stale indoor air and brings in outdoor air while recovering heat from the air leaving the house, so the fresh air arrives tempered instead of frigid. The Minnesota Department of Commerce explains the need simply: air exchangers provide the fresh air for occupants that used to be provided by leaky houses, before we insulated and sealed them properly. Minnesota's residential energy code requires new dwellings to have a balanced mechanical ventilation system, which is why nearly every home built here in the last decade has one.
How often should an HRV or ERV be cleaned?
The Minnesota Department of Commerce recommends that HRV and ERV filters be cleaned or replaced in the spring and the fall, and that the exterior vent openings be checked for blockages from snow, debris, or insects. The heat exchange core and the intake and exhaust ductwork need attention less often but do need it, typically alongside a whole-house duct cleaning. Two filter checks a year plus a deeper clean when you do the ducts is a realistic schedule.
What happens if the air exchanger is never maintained?
Airflow falls first, which quietly undoes the reason the system was installed. A loaded filter, a dusty core, or an exterior hood packed with snow or a wasp nest reduces the fresh air the house is getting, and Minnesota's code is written around a specific delivered rate, not around having the equipment present. The symptoms are the ones tight houses get without ventilation: stuffiness, lingering odors, and window condensation in winter.
Is the air exchanger part of a normal air duct cleaning?
It is a separate scope, and it should be quoted separately rather than assumed. The ducts that run to and from the unit are part of the duct system, and the unit itself, its filters, and its exterior hoods are their own job. When we quote an East Metro home with an HRV, we tell you up front what the exchanger adds so there is no surprise at the end.