ERV vs HRV in Maryland: Which Air Exchanger Is Best?

Our take

What works in Maryland

Most Maryland homes are better served by an ERV, with a few exceptions.

Maryland's humid summers and moderate winters put the bigger seasonal moisture load on the house in July and August. An ERV is the usual pick, with Chesapeake-area homes needing a close eye on outdoor hoods after storms.

Why that pick

Summer humidity is the larger seasonal load, and an ERV keeps part of it out.
Winters are cold enough to matter but rarely extreme, so heat and moisture recovery both earn their keep.
In the drier or hotter parts of the state, an ERV also helps hold onto some indoor moisture in winter.

When the other type wins

Tight houses that show winter window condensation, and higher-elevation or northern homes with long heating seasons, can be better served by an HRV.

Experts still disagree at the margins. Building scientists writing on Green Building Advisor argue over ERV versus HRV in cold climates: some say the humidity benefit of an ERV is small there, others that tight cold-climate homes fight winter moisture and want it exhausted. The tie-breaker is your house, not the map.

Choose an ERV if…

you run air conditioning through humid summers and want less humidity coming in with the fresh air;
your winter indoor air runs dry, or you run a humidifier most of the winter (an ERV returns part of the moisture);
cooling season matters as much as heating season where you live.

Choose an HRV if…

your house builds up winter moisture, with window condensation or damp corners, because an HRV does not put moisture back;
you have a long, cold, heating-dominated winter and little or no air conditioning;
outdoor winter air is damp (marine climates), so you want no outdoor moisture passed inside.

Neither one is a dehumidifier. If the house is sticky, size the air conditioning correctly or add a dedicated dehumidifier.

The 60-second version

HRV vs ERV vs “air exchanger”

All three names describe the same idea: a fan pulls stale indoor air out and fresh outdoor air in, and the two streams pass through a core so the incoming air borrows some of the outgoing air’s temperature.

	HRV	ERV	“Air-to-air exchanger”
What it recovers	Heat only	Heat and part of the moisture	A general name for either one
Typical core	Aluminum or plastic plates	Paper-like or polymer membrane, or an enthalpy wheel	Check the label on your unit
Moisture	Not passed between air streams; condensation drains away	Partly passed between air streams	Depends on which type you have
Usually best for	Cold, heating-dominated climates and tight homes with winter moisture problems	Humid summers, dry winters, homes with air conditioning or a humidifier	—
Watch for	Very dry winter air in a very tight house	It is not a dehumidifier, and most ERV cores cannot be washed	—

HRV - heat moves through metal or plastic plates. The two air streams never touch, and moisture is not passed along.

ERV - the core also lets water vapor pass between streams, so part of the indoor moisture is kept in winter and part of the outdoor moisture is kept out in summer.

What is an “air-to-air exchanger”? It is a common everyday name for an HRV or ERV. Some people also use “air exchanger” for a simple fresh-air duct with a motorized damper tied to the furnace. That brings outdoor air in but recovers no heat or moisture, so it is a different (and less efficient) thing. If you are not sure what you have, look up your model number.

One shortcut you will hear is that an HRV has a metal core and an ERV has a non-metallic one, and Lifebreath’s own FAQ says exactly that. It is a good rule of thumb, but plastic HRV cores exist, so go by the model number and the manual, not the rule.

Efficiency is measured as sensible recovery efficiency (SRE). ENERGY STAR Canada’s Tier 2 requirement is 65 percent at 0C (32F) and 60 percent at -25C, and the 2021 IECC uses the same 65 percent at 32F for the coldest climate zones. Units in our lookup range from about 68 to 84 percent, depending on model.

Climate check

Maryland by region

Maryland spans IECC climate zones 4A to 5A. Zones are assigned county by county, so check your own county before you decide. The higher the number, the colder the winters; the letter tells you whether the climate is moist (A), dry (B) or marine (C).

Where	What it is like	Best fit
Baltimore-Washington corridor and Central Maryland	Zone 4A - hot humid summers, cool winters	ERV
Eastern Shore and Southern Maryland	Zone 4A - humid, coastal, storm exposure	ERV
Western Maryland (Cumberland, Garrett County)	Zone 5A - colder, snowier	Either

Zone lists come from the DOE Building America county guide and standard IECC maps. Verify your county with your local building department.

Why bother?

Why fresh air matters in Maryland

Modern homes are built tight on purpose, because a tight house wastes less energy. The catch is that a tight house also stops leaking stale air out, so whatever is made inside stays inside.

The U.S. EPA notes that people spend roughly 90 percent of their time indoors and that indoor concentrations of some pollutants are often two to five times higher than outdoors. Ordinary daily life adds to that: cooking and gas appliances, cleaning products and furniture that release VOCs, carbon dioxide from breathing, moisture from showers and laundry, pet dander and dust. Radon, a naturally occurring gas, can also collect in tight homes, and the EPA recommends testing every home for it. A ventilator does not remove radon, so testing is still the only way to know.

A balanced ventilator fixes the imbalance by bringing in about as much air as it exhausts. Both the Minnesota and Washington codes, for example, require the two flows to match within 10 percent. That is different from a bathroom fan alone, which pulls replacement air in through cracks, unfiltered and unconditioned. The heat or energy recovery core is what makes it practical to ventilate all winter and summer without paying for all of that outdoor air twice.

How much? The code formula is CFM = (0.01 x square feet) + 7.5 x (bedrooms + 1). A 2,000 sq ft, 3-bedroom home needs about 50 CFM running continuously. Use the CFM checker to see whether your unit covers your home.

Read this before you touch a setting

Do not run your HRV or ERV off its humidistat if you have a whole-house humidifier

You are more likely to be fighting moisture than adding it in Maryland, but plenty of homes still have a whole-house humidifier, and the same rule applies to them. Most ventilators have a humidity control called a humidistat or dehumidistat (some labels say “RH”). When indoor humidity rises above its setpoint, it kicks the ventilator to high speed to exhaust humid indoor air and bring in drier outdoor air. NRCan and Lifebreath both describe it exactly that way. It is a useful feature in a home that has no humidifier. In a home that does, the two controls work against each other:

They chase each other in a loop. The humidifier adds moisture until the house reaches its setpoint. The ventilator’s humidity control sees that humidity and goes to high speed, exports the moisture you just paid to add, and pulls in dry outdoor air. The house drops below the humidifier’s setpoint, and the humidifier starts again.
You pay for the same water twice. Humidifiers use substantial energy to evaporate water, and running the fan on high adds fan energy and more incoming air to heat. The core recovers only part of that heat, and you also draw more mineral scale through the humidifier.
Humidity is the wrong signal for fresh air. A humidity reading says nothing about carbon dioxide, cooking fumes, VOCs or stale air. The ventilator can sit at low speed for days when humidity looks fine while the air quality slips. Code ventilation rates are set by house size and bedrooms, not by humidity.
Cold weather makes it worse. Humidified indoor air carries more moisture into the core, and in freezing weather that moisture is what turns to frost on it, so you can trigger more defrost cycles and lose fresh airflow when you need it.

What to do instead

Run the ventilator on its own schedule: continuous low speed, or a timer or intermittent mode that delivers the airflow your home needs (see the formula above).
Turn the ventilator’s humidity boost to its highest setting or to off. The exact label varies, so check your manual.
Let the humidifier’s own humidistat hold the indoor humidity, ideally one that adjusts to the outdoor temperature. Lower the target as it gets colder, and if you see moisture on the windows the target is too high.
If you are humidifying constantly, consider an ERV. A good ERV returns part of the moisture in the exhaust air, and one building-science discussion points out that this can save much of the energy a humidifier would burn.
If you do not have a humidifier and your winter problem is too much moisture, the ventilator’s humidity control is helpful. The colder the outdoor air, the more moisture a ventilator can shed.
In summer, neither an HRV nor an ERV is a dehumidifier, and Lifebreath’s FAQ says so plainly.

This explains how the controls interact, based on how manufacturers describe the humidity function. It is not a manufacturer prohibition, so check your own manual for the exact wording on your model.

Keep it working

Maintaining your HRV or ERV in Maryland

A neglected ventilator quietly moves less air every month. A clogged filter or dirty core can cut airflow a lot before you notice anything.

The schedule

Task	How often	Source
Filters	Every 1-3 months. Clean or replace before they look clogged.	NRCan, RenewAire (about every 3 months), Panasonic (vacuum every 2-3 months)
Exterior hoods and screens	Every 1-3 months and after storms. Screens should stay at 1/4-inch mesh or larger.	NRCan
Core	Inspect and clean every 6 to 12 months, and at least once a year before the heating season. Follow your manual.	NRCan (every 6 months), Rise (1-2 times a year)
Condensate drain (HRV)	Every 6 months. Pour 2-3 liters of warm water through it and clear blockages.	NRCan
Fans and interior	Every 3-6 months. Gently brush or vacuum the blades. Lubricate only if your manual says to.	NRCan
Professional check and balancing	Annual service is a good habit. Airflow balancing after installation, then every 3-5 years or after duct changes.	NRCan, Rise

Your Maryland calendar

Season	What to do in Maryland
Spring (Mar-May)	Replace or vacuum the filters. If your annual core cleaning falls in spring, do it now. Check both exterior hoods for nests, lint and debris. Get ready for storm season: clear the hoods and confirm the dampers move.
Summer (Jun-Aug)	Check the condensate drain and pan. Smell the supply vents for mustiness. Filters monthly if the air is hazy or dusty.
Fall (Sep-Nov)	This is the best single time for the annual core cleaning, before the heating season starts. Replace filters and clear the hoods. Check the ventilator's humidity-control setting, especially if you have a whole-house humidifier.
Winter (Dec-Feb)	Mild winters: a mid-season filter check is usually enough. Confirm the unit is on its normal fresh-air schedule.

How to clean the core

First, know which kind of core you have. The rule is different for each, and washing the wrong one ruins it.

Rinsable aluminum HRV core

Lifebreath’s HRV manual and Honeywell’s HR line describe cores like this as washable:

Vacuum first.
Soak and rinse in warm, soapy water.
Let it dry completely.

Vacuum-only ERV core

RenewAire’s manual says “do not wash the energy exchange core.” Honeywell says the same for its ER models:

Remove the filters first.
Vacuum the exposed faces with a soft-brush attachment.
Keep it away from water.

Switch the unit off and unplug it. Open the access door.
Pull the filters and set them aside. Vacuum the filter compartment.
Note the core’s orientation, then slide it out by gripping both ends and pulling evenly.
Inspect it for dust, pet hair and any sign of mold.
Clean it the way your core allows (see above). If your manual is silent, vacuum only.
Let it dry fully if it got wet, then reinstall it the same way up. Push on the sides, not the center.
Reinstall clean filters (Lifebreath: rinse them in cold water or mild soapy water, do not wring them out, no hot water), close the door and restore power.
Check the drain and both exterior hoods while you are at it.

Never

Use bleach, chlorine or cleaning solutions on a core.
Use a pressure washer, or put a core in the dishwasher.
Use very hot water, or soak or scrub an ERV membrane.
Adjust balancing dampers without airflow measurement tools.

Not sure which core you have? Look up your model and we will show the cleaning rule for it.

Local factors

What is different about Maryland

Humid summers: keep the moisture out and the drain clear

In Maryland, the muggy months are when the ventilator is working against the weather. An ERV reduces how much moisture rides in with the fresh air, but it does not dehumidify. As one building-science writer puts it, reducing the moisture coming in is not the same as dehumidifying the air already in the house. If the house still feels sticky, the fix is properly sized air conditioning or a dedicated dehumidifier, not a bigger ventilator.

Check the condensate drain and drain pan at least twice a year, and sooner if the unit sits in a damp attic or basement. A slow drain, water around the cabinet or a musty smell at the supply vents means it needs attention.

Coastal salt air: check hoods and screens more often

Salt spray corrodes metal hoods, dampers and fasteners, and salt and debris clog screens. Look at both exterior hoods every month or two, keep the screens at 1/4-inch mesh or larger (finer mesh clogs faster), and replace corroded hoods or dampers early rather than late.

Storm season: before and after

Before storm season, clear both hoods and confirm the dampers open and close. After a storm, remove debris from the hoods. If the house took on water or the roof leaked, have the core, ducts and drain looked at before you run the unit again, because a wet core can grow mold.

Codes

Ventilation rules in Maryland

Most states adopt a version of the International Residential Code and the International Energy Conservation Code, and the edition varies by state and even by city. The 2021 IECC (section R403.6.1) requires dwelling units in climate zones 7 and 8 to have a balanced heat or energy recovery system with at least 65 percent sensible heat recovery efficiency at 32F.

In the climate-zone lists we used, Maryland does not have counties in zone 7 or 8, so that specific requirement does not apply. Local code may still require mechanical ventilation, so check with your building department.

The whole-house ventilation rate in the 2021 code (and in ASHRAE 62.2) comes from a simple formula: CFM = (0.01 x square feet) + 7.5 x (bedrooms + 1). A 2,000 sq ft, 3-bedroom house works out to 50 CFM continuous. Our model and CFM checker does the math for you and compares it to your unit.

Not legal advice. Codes change, and cities can amend them. Confirm with your local building department.

Quick answers

Maryland FAQ

Should I get an ERV or an HRV in Maryland?

Most Maryland homes are better served by an ERV, with a few exceptions. Tight houses that show winter window condensation, and higher-elevation or northern homes with long heating seasons, can be better served by an HRV.

Can I run my HRV or ERV on a humidistat if I have a whole-house humidifier?

We recommend against it. The humidifier adds moisture, and the ventilator's humidity control responds by running on high speed to exhaust it and bring in drier outdoor air, so the two controls chase each other. That wastes energy, can increase frost and defrost cycles in cold weather, and ties fresh air to a humidity reading instead of your home's actual ventilation needs. Run the ventilator on continuous low or a timer, set the humidity boost to its highest setting or off (check your manual), and let the humidifier control its own humidity.

How often should I clean my HRV or ERV core?

Inspect and clean it every 6 to 12 months, and at least once a year before the heating season, following your manual. Filters need attention every 1 to 3 months. Aluminum HRV cores are often rinsable in warm, soapy water, while many ERV cores, including RenewAire's and Honeywell's ER models, are vacuum-only and must not be washed.

Is an HRV or ERV required in Maryland?

It depends on the code your city or county enforces. The 2021 IECC only requires an HRV or ERV in climate zones 7 and 8, and Maryland has no counties in those zones in the lists we used, but many places still require some form of whole-house mechanical ventilation in new homes. Check with your building department.

What is the difference between an air exchanger, an HRV and an ERV?

'Air exchanger' or 'air-to-air exchanger' is an everyday name for a balanced ventilator that swaps stale indoor air for fresh outdoor air through a core. An HRV transfers only heat. An ERV transfers heat and part of the moisture. Some people also call a simple fresh-air duct with a damper an air exchanger, but that recovers no heat or moisture.

How do I find out what unit I have and how many CFM it moves?

Find the model number on the label, usually on the outside of the cabinet, inside the access door or on the end of the core, and enter it in our HRV and ERV model lookup. It shows the unit type, the rated airflow, the duct size and the correct way to clean the core.

ERV vs HRV in Maryland