Should a Minnesota house have an HRV or an ERV?
A house that runs humid in winter, with sweating windows, needs an HRV; one that runs dry does better with an ERV, which keeps some moisture in. State code requires balanced ventilation in new homes. National guides put a ducted unit at $1,300–$2,500 installed.
Key points
- Both swap stale indoor air for outdoor air and recover heat from the outgoing stream. An ERV also moves some moisture.
- A tight house with wet windows and a full household usually wants an HRV. A small, sparsely occupied house that runs dry may do better with an ERV.
- Minnesota's residential energy code (Minn. R. 1322.0403) requires balanced mechanical ventilation sized by floor area and bedrooms.
- Both need a defrost strategy for Minnesota cold, clean filters and cores, and outside hoods kept clear.
- Published national ranges put a whole-house unit tied into existing ducts at $1,300–$2,500 installed.
Choose an HRV if your Minnesota house runs humid in winter, with windows that sweat or frost, and an ERV if it runs dry and you run a humidifier to reach the low 30s percent. Both bring in fresh air and recover heat from the outgoing air. Older Minnesota houses leak: stale air, cooking smells and shower moisture escape through gaps around windows, sill plates and attic hatches, and a lot of heat goes with them. Newer houses, and older ones that have been air-sealed and insulated, don't leak like that. Without a planned way to exchange air, moisture builds up, smells linger, and windows sweat at humidity levels that wouldn't bother a drafty 1950s rambler. An HRV or ERV is that planned exchange, and our ventilation service page covers how we install and service them.
What do HRVs and ERVs actually do?
Both are a box with two fans and a core. One fan pulls stale air out of the house, usually from bathrooms and the kitchen or from the furnace return. The other brings in the same amount of fresh outdoor air. The two streams pass through the core without mixing, and the outgoing air warms the incoming air.
- A heat recovery ventilator (HRV) transfers heat only. Moist indoor air goes out, dry winter air comes in, and the house gets drier.
- An energy recovery ventilator (ERV) transfers heat and some moisture. Part of the moisture in the outgoing air goes back into the house instead of outside.
Neither one is a heater, an air conditioner, a humidifier or a dehumidifier. They exchange air and soften the temperature and humidity swing that comes with it.
| HRV | ERV | |
|---|---|---|
| What the core transfers | Heat only | Heat and some moisture |
| Effect on winter humidity | Dries the house | Keeps some moisture in |
| Best Minnesota fit | Tight houses with wet windows and a full household | Smaller or lightly occupied houses that run dry |
| Summer | Brings outdoor humidity in with the fresh air | Slows some of the incoming humidity |
| Condensate drain | Needs one, kept in heated space | Check the manual for the model |
| Deep cold | Needs a defrost mode | Needs a defrost mode too |
What does Minnesota code require for ventilation?
The Minnesota Residential Energy Code covers this in Minn. R. 1322.0403. It requires a balanced mechanical ventilation system, meaning the air intake is within 10 percent of the exhaust output. HRVs and ERVs have to meet HVI Standard 920 or be certified by a registered engineer, and be installed per the manufacturer's instructions.
The rule sizes the system with a simple formula:
- Total ventilation (cfm) = 0.02 × conditioned square feet + 15 × (bedrooms + 1)
- Continuous ventilation must be at least half of the total, and never less than 40 cfm.
For a 2,000-square-foot house with three bedrooms: 0.02 × 2,000 = 40, plus 15 × 4 = 60, for a total of 100 cfm, with at least 50 cfm running continuously.
That rule applies to homes built under the current code. An older house isn't required to add one, but if you tighten it up a lot with new windows, spray foam or serious air sealing, it can end up needing mechanical ventilation anyway.
Which one fits which Minnesota house
The question to ask is which way your house leans in February.
HRV: a tight house with a full household, lots of cooking and showers, and windows that sweat or frost even without a humidifier running. An HRV swaps that moist air for dry outdoor air, and it's the traditional choice in cold climates like ours for exactly that reason.
ERV: a small house or townhome with one or two people, where the air runs dry in winter and you're running a humidifier just to reach the low 30s. An ERV throws less of your moisture away, so the humidifier works less. In summer an ERV also slows down the humidity coming in with fresh air, which helps the AC a little. It isn't a dehumidifier, though. A damp basement still needs a whole-house dehumidifier or more AC run time.
If you're adding moisture with a whole-home humidifier and also have wet windows, the ventilation isn't keeping up, and that's worth a look before anything else.
How do HRVs and ERVs handle frost in cold weather?
When it's well below freezing outside, moisture in the outgoing air can freeze inside the core. Both types handle this with a defrost mode: some units briefly recirculate indoor air through the core, others close the fresh-air damper for a few minutes. During defrost, fresh air stops, so in a long cold snap the unit spends more of its time defrosting and delivers less fresh air. HVI-certified ratings let you compare how units perform at cold test conditions, which matters more in Minnesota than in milder climates.
HRVs produce condensate and need a drain, so the drain line has to stay in heated space and flow freely. Outside, the intake and exhaust hoods need to stay clear of drifted snow and frost in winter and cottonwood fluff in June.
| What you notice | Likely cause | What to do | Who does it |
|---|---|---|---|
| Outside hoods frosted over or buried | Deep cold or drifting snow | Clear the hoods | You |
| Unit iced up or dripping | Defrost setting, a blocked drain, or unbalanced airflow | Check the drain line, then have defrost and balance checked | Technician |
| House feels drafty during a cold snap | Airflows out of balance | Have the airflows measured and balanced | Technician |
| Windows still sweat | Ventilation rate too low, or the humidifier set too high | Turn the humidifier down first, then have the rate checked | You, then a technician |
| Musty or stale smell | Dirty filters or core | Clean them per the manual | You |
Why does a ventilator need balanced airflow?
A ventilator only helps if its two airflows match. Run more exhaust than supply and the house goes under negative pressure, which in a tight house can pull exhaust back down a gas water heater's vent. That backdraft is a carbon monoxide hazard, and it is another reason to keep CO alarms current. Airflows should be measured and balanced when the unit is installed and rechecked after any duct work.
There are two common hookups. A fully ducted system has its own small ducts: fresh air to bedrooms and living areas, stale air from bathrooms and the kitchen. A simplified system ties into the furnace return and uses the furnace blower to spread the fresh air, which is cheaper to install but means the blower runs whenever the ventilator does.
Upkeep and cost
Both types need their filters cleaned or replaced every few months, the core cleaned per the manufacturer's manual, the drain checked, and the hoods kept clear. It fits naturally into a fall maintenance visit; our maintenance visits run $129–$349 depending on the equipment. We service ventilators on maintenance visits in Minneapolis and the suburbs. We service the common ventilator brands, including Lifebreath and Broan-NuTone.
On price, published national ranges from Fixr and Trane put a typical whole-house unit tied into existing ductwork at $1,300–$2,500 installed, with ERVs usually costing more than HRVs and dedicated duct runs adding to it. Our own installed range for indoor air quality equipment is $350–$2,800, quoted flat-rate in writing first.
What to do next
Put a hygrometer in the main living area for a week in January and watch the windows. Wet glass at modest humidity points to an HRV; dry air despite a humidifier points to an ERV. For the rest of the winter air picture, see indoor air quality in a Minnesota winter. If a ventilator is iced up, noisy or not running, call 612-429-3465, open daily 7am to 9pm. The $79 trip charge on the service call is waived when you approve the repair.
Common questions about air quality
Can I shut my HRV off in winter to save heat?
You can, but in a tight house moisture and stale air build up fast, which is why code calls for a continuous ventilation rate. If the HRV seems to be chilling the house, the usual causes are a dirty core, a defrost problem or airflows that are out of balance. A working unit recovers a good share of the heat from the air it sends out.
Why is my HRV's outside hood frosted over?
In deep cold, frost can build on the intake and exhaust hoods, and drifting snow can bury them. Clear the hoods first. The core has its own defrost mode, so if the unit keeps icing up, drips water, or the house gets drafty during cold snaps, have the defrost setting and the airflow balance checked.
Does an ERV replace a dehumidifier?
No. An ERV slows down the moisture that comes in with fresh outdoor air in summer, which takes a little load off the AC. It can't pull out moisture the house already has. A basement that smells musty in July needs a dehumidifier or more AC run time, not a different ventilator.
Isn't a bathroom fan enough ventilation?
In a leaky older house, a good bath fan and range hood often cover it. In a tight house, exhaust-only fans pull air out with no matched supply, which leaves the house under negative pressure and can draw exhaust down a water heater vent. That is why Minnesota's code for new homes asks for balanced ventilation, with intake within 10 percent of exhaust.