Why does a tight house need planned fresh air?
Air leaks do a job nobody planned. In an older house, stale air, shower steam and the smell of last night's fish slip out through cracks all winter while cold air slips in to replace them. You pay for that on the gas bill, but the house airs itself out. Tighten it with new windows, blown-in insulation, spray foam or a utility air-sealing job and the accidental exchange mostly stops, and so does the drying it used to do. Frost creeps up the window corners, the bathroom mirror stays fogged, and a closed bedroom smells stale by morning.
Mechanical ventilation replaces the leaks with an exchange you control. Throwing warm air outdoors in January costs heat, so in Minnesota that job usually goes to a heat recovery ventilator (HRV) or an energy recovery ventilator (ERV), which reclaim part of that heat on the way out. Our winter air quality guide shows where ventilation fits among the other fixes.
What an HRV or ERV does, and what it doesn't
Inside the cabinet are two blowers and a heat exchange core. One blower pulls stale air from bathrooms, the kitchen or the furnace return and sends it outside. The other brings in an equal volume of outdoor air. Inside the core the two airstreams travel through alternating thin passages, so heat crosses from the warm side to the cold side while the air itself stays separate. An ERV's core also hands some moisture from one stream to the other.
Don't expect either one to fix temperature or humidity on its own. A ventilator trades air; the core only softens how cold, hot, dry or damp the incoming air is compared with what went out. If the house is too dry, that's a humidifier job. If the basement is damp in July, it's a dehumidifier job.
HRV or ERV: which fits a Minnesota house?
| What to compare | HRV | ERV |
|---|---|---|
| Recovers heat from the outgoing air | Yes | Yes |
| Moves moisture between the air streams | No | Some |
| Effect in a Minnesota winter | Dries the house | Holds some moisture in |
| Effect on a humid July day | Brings in moisture the AC has to remove | Keeps some of it out, but isn't a dehumidifier |
| Usual fit | Tight house, full household, windows that sweat | Smaller or lightly occupied house that runs dry |
| Condensate drain | Needed, in heated space | Depends on the model |
| Defrost strategy for Minnesota cold | Needed | Needed |
In cold, heating-dominated climates, HRVs are the long-standing default, because most tight houses run humid in winter and need moisture sent outdoors. An ERV earns its place where the opposite happens: few occupants, not much cooking or showering, and air that stays dry even with a humidifier running. If you're not sure which way your house leans, a hygrometer and a close look at the windows through February will tell you. Our ERV vs HRV guide goes deeper.
What does Minnesota code require for ventilation?
Homes built under the Minnesota Residential Energy Code need balanced mechanical ventilation under Minn. R. 1322.0403, and the supply and exhaust flows have to land within 10 percent of the design capacity. The rule sizes the system from floor area and bedrooms: total ventilation in cfm equals 0.02 times the conditioned square footage, plus 15 times the number of bedrooms plus one. At least half of that total has to run continuously, with a floor of 40 cfm. A 2,500-square-foot house with four bedrooms works out to 50 plus 75, or 125 cfm total, with at least 62.5 cfm of that running continuously.
The same rule calls for HRVs and ERVs that pass HVI Standard 920's 72-hour cold-weather test at -13°F (or carry a registered engineer's certification), at least a MERV 4 filter on the outdoor air, intake openings at least 12 inches above grade that stay reachable for maintenance, and a backflow damper that closes when the system is off.
Older houses aren't required to add ventilation. But once a house gets tightened, whether through new windows or the insulation and air-sealing programs that Xcel Energy and CenterPoint Energy run, it's worth asking whether it now needs one. In newer suburbs such as Woodbury, many houses already have an air exchanger, and those mostly need upkeep; see maintenance in Woodbury. Ventilation work can need a permit, too; Saint Paul, for one, issues warm air and ventilation permits, and our HVAC permit guide covers who issues what.
Winter in Minnesota: defrost, drains and buried hoods
- Defrost. Well below zero, the damp air leaving the house can ice up the core. Depending on the design, the unit either recirculates warm house air through the core or closes its outdoor damper until the ice clears. Through a week of -20°F nights, defrost takes a bigger share of every hour, so less fresh air comes in; that's expected.
- Drains. Keep an HRV's condensate line inside the heated part of the basement with a steady downhill run. One routed along a cold rim joist can freeze and back water into the cabinet.
- Hoods. Drifts bury low intake and exhaust hoods, and frost can close them off. Check them after every big storm, and again in June, when cottonwood fluff mats the screens.
- Pressure and combustion safety. If exhaust outruns supply, the house runs at a slight vacuum, and in a tight house that suction can reverse the draft on a gas water heater and spill its exhaust into the basement. Balancing prevents it. Minnesota law requires a working carbon monoxide alarm within 10 feet of every sleeping room; see our CO alarm guide.
How the install and balancing work
- We size it. Floor area, bedroom count and how the house behaves in winter decide the airflow and whether an HRV or ERV fits.
- We pick the hookup. The simpler hookup connects to the furnace's return duct and borrows the furnace fan to distribute outdoor air; it's the cheaper install, with one catch: the furnace fan has to run any time the ventilator is moving air. The fully ducted version runs dedicated small ducts, with supply to the bedrooms and main rooms and exhaust pickups in the baths and kitchen.
- You get a written quote. A flat price for the unit, the ductwork and the controls before any work.
- We install it. Hang the unit in the basement or mechanical room, run insulated ducts to the wall hoods, put the intake where drifts won't bury it and at least 12 inches above grade, run the drain, and wire the controls.
- We balance it. Measure supply and exhaust airflow and set them to match within the 10 percent the code allows.
- We walk you through it. Filters, core, defrost and control modes, and whether the manufacturer wants the unit registered for its full parts warranty.
When an existing ventilator ices, rattles or quits, the usual causes are a plugged core or filters, a failed motor, a stuck damper or a frozen drain. A repair visit is a $79 trip charge, waived when you approve the repair.
How much does ventilation cost, and how do you keep it running?
An HRV or ERV sits toward the top of our $350–$2,800 installed range for air quality equipment, depending on the unit, the hookup and how much duct work it takes. You get a written flat-rate quote before work starts, and installs carry our 2-year labor warranty on top of the manufacturer's parts warranty. National figures from Fixr and Trane give a typical range of about $1,300–$2,500 for a whole-house unit connected to existing ducts. ERVs tend to cost more than HRVs, and new dedicated duct runs push the price up. If the furnace is due for replacement, that's a good time to tie a ventilator into the new return; our furnace replacement cost guide covers that project. Our published prices are all on the pricing page, and HVAC costs in Minneapolis lays out furnace and AC numbers.
A ventilator with clogged filters or a dirty core keeps running while it moves less air, so nobody notices until the windows sweat. A fall furnace tune-up, from $129, is the natural time to clean it, and you can ask us about a maintenance plan. We service Lifebreath, Broan-NuTone and Aprilaire fresh air equipment along with other makes, and install it where it fits the house. For the rest of what we work on, see indoor air quality.
What's included with hrv & erv ventilation?
- Airflow sized from floor area and bedroom count with Minnesota's code formula
- HRV or ERV chosen by how your house runs in winter, wet or dry
- Hookup to the furnace return, or dedicated ducts to bedrooms, baths and kitchen
- Intake at least 12 inches above grade as code requires, placed clear of drifting snow
- Condensate drain run in heated space on units that need one
- Supply and exhaust airflows measured and balanced within 10 percent
- 2-year labor warranty on installs, plus the manufacturer's parts warranty
HRV & ERV Ventilation questions
HRV or ERV: which is better for Minnesota?
Neither wins everywhere. An HRV suits a tight house that runs humid in winter, with sweating windows and a full household, because every hour it sends damp house air out and brings dry winter air in. An ERV suits a house that runs dry, since its core keeps some moisture indoors. In cold climates HRVs are the long-standing default, but your house's winter humidity should make the call.
Does my house need one?
Probably, if it's a newer house or an older one that's been tightened up. Minnesota's current residential energy code requires balanced mechanical ventilation, so many newer houses already have one. Older houses usually leak enough air on their own until new windows, spray foam or air sealing change that. Wet windows at modest humidity, lingering smells and stuffy bedrooms are the signs that a house has crossed that line.
Why does the air exchanger make one room cold?
A clogged core is the usual reason, followed by defrost trouble and airflows that have drifted out of balance. A dirty core recovers less heat, so fresh air arrives colder than it should, and the nearest supply grille feels it first. In long cold snaps the unit also spends more time defrosting. Cleaning the core and filters and rebalancing the airflow usually fixes it, and none of it calls for shutting the unit off.
How often should an HRV or ERV be cleaned?
Check the filters a few times a year and wash or replace them per the manual. Clean the core on the manufacturer's schedule, usually at least once a year, and fall is a good time. Clear the outside hoods after big snowstorms and again in June when cottonwood flies, and make sure the condensate drain flows. It fits neatly into a fall furnace tune-up.
Why is my HRV dripping or icing up?
Ice forms when moisture in the outgoing air freezes inside the core during deep cold, and the defrost cycle is supposed to clear it. Dripping usually means a plugged or frozen condensate drain, or a drain line routed through a cold space. Clear the outside hoods first, then have the defrost setting, the drain and the airflow balance checked.
Can you add an HRV or ERV to an older house?
Usually. The least invasive retrofit connects to the furnace's return duct and uses the furnace fan to carry outdoor air through the existing ducts, so only a couple of new duct runs are needed. A fully ducted system with its own supply and exhaust runs costs more in a finished house, because of the walls and ceilings it has to pass through. Boiler homes with no ducts need that fully ducted version or another approach.
Sources
- Minn. R. 1322.0403 revisor.mn.gov