HRV vs ERV: Which Ventilator Does Your House Need?

A heat recovery ventilator (HRV) and an energy recovery ventilator (ERV) do the same core job: continuously exchange stale indoor air for fresh outdoor air, while passing the outgoing air through a core that transfers most of its heat to the incoming air. You get ventilation without throwing away the energy you paid to put into the air.

The difference between them is one thing: an ERV also transfers moisture. An HRV doesn't.

That single distinction is what the choice turns on.

Why a tight house needs one

Older houses ventilate by accident — through leaks in the attic floor, the rim joist, and around windows. It's uncontrolled, weather-dependent and inefficient, but it does exchange air.

Seal a house properly and that accidental ventilation goes away. What's left is:

• Moisture from cooking, bathing, laundry and simply breathing, with nowhere to go
• Carbon dioxide accumulating with occupancy
• Cooking byproducts, cleaning product vapours and off-gassing from materials
• Odours that linger

The answer isn't to leave the house leaky — random leaks ventilate unpredictably and only when the weather drives them. The answer is to seal it properly and ventilate deliberately. See how to air seal a house and why your house feels stuffy.

How do an HRV and an ERV work?

Two fans, two airstreams, one core:

1. Stale air is drawn from moisture- and odour-producing rooms — bathrooms, kitchen, laundry.
2. Fresh air is drawn from outside.
3. The two streams pass through a core where energy transfers between them without the airstreams mixing.
4. Fresh, tempered air is delivered to living spaces and bedrooms; stale air goes outside.

In winter: outgoing warm air preheats incoming cold air, so you're not dumping heat outside. In summer: outgoing cool air pre-cools incoming warm air.

The HRV core transfers sensible heat only — temperature.

The ERV core transfers sensible heat and latent heat — a portion of the water vapour moves between the airstreams too.

The humidity difference in practice

So:

• Humid summers → an ERV reduces how much moisture your air conditioner has to remove. Real benefit.
• Cold winters with high indoor humidity — window condensation, damp bathrooms — → an HRV removes that moisture. Real benefit.
• Cold winters with low indoor humidity — static shocks, dry skin, cracking woodwork — → an ERV keeps some of what little moisture you have.

Choosing

The usual guidance:

• Cold, heating-dominated climate → HRV
• Hot, humid, cooling-dominated climate → ERV
• Mixed climate → ERV is often the better all-rounder

But judge by your actual indoor humidity, not the climate label. Get a hygrometer and observe across a season. A well-occupied, tightly sealed house in a cold climate that runs at high winter humidity wants an HRV. A sparsely occupied one in the same climate that runs bone dry wants an ERV.

Target indoor relative humidity is generally in the 30–50% range, lower in the coldest weather to avoid window condensation. See home humidity control.

Sizing

Ventilation rate is based on the size of the house and the number of occupants — the recognised residential ventilation standard sets the method, and building codes reference it. Your local code governs.

Two practical points:

• Bigger isn't better. Over-ventilating wastes energy and, in winter, dries the house out excessively.
• Variable speed matters. A unit that runs continuously at a low rate with a boost for showers and cooking performs better than one cycling between off and full.

Get the sizing from the standard applicable in your jurisdiction, or from a contractor who works to it.

Ducting options

Fully ducted (dedicated). Its own supply and exhaust ductwork — exhaust from bathrooms, kitchen area and laundry; supply to bedrooms and living spaces. Best performance, highest cost, easiest during construction or a major renovation.

Simplified / partially ducted. Exhaust from a couple of key locations, supply to a central area. Cheaper, less even distribution.

Integrated with existing forced-air ducts. The ventilator ties into the furnace or air handler ductwork. Cheapest retrofit route, but distribution depends on the air handler running — many installations use a control that periodically runs the blower to circulate the fresh air.

Note on kitchens: a range hood should be separately ducted directly outside, not routed through a recovery ventilator core — grease fouls the core. See gas stove indoor air quality for why kitchen exhaust matters in its own right.

Cold-climate details

Two things to check on any unit going into a cold climate:

Defrost strategy. In sub-freezing weather, moisture in the outgoing air can freeze on the core. Units handle this with recirculation defrost, a preheater, or periodic reversal. A unit without an adequate defrost strategy will ice up.

Preheating. Some installations add a preheater on the fresh air intake to protect the core and avoid delivering very cold air.

Ask specifically how the unit you're quoted handles defrost at your design temperature.

Running cost and maintenance

Electricity: two fans, comparable to running a bathroom fan continuously. Modest. Efficient units use ECM motors. Estimate with the electricity cost calculator.

The heating and cooling attached to the air exchange is the larger number, and it's exactly what the core reduces. Certified units publish sensible recovery efficiency (and for ERVs, total recovery efficiency) — compare those figures between products.

Maintenance, and it's not optional:

• Clean or replace the filters on schedule — a clogged filter kills airflow and the unit's performance quietly
• Clean the core per the manufacturer's interval
• Check the intake and exhaust hoods outside for blockage, insects and nests
• Check the condensate drain if the unit has one

A neglected recovery ventilator delivers far less air than its rating and gives no warning. Put it on a schedule.

What it isn't

• Not an air conditioner or heater. It tempers incoming air; it doesn't condition the house.
• Not a dehumidifier. An ERV moderates moisture transfer; it doesn't actively remove humidity. See cost to run a dehumidifier.
• Not a substitute for spot exhaust. Bathroom fans and range hoods still do a job a whole-house ventilator can't — see bathroom exhaust fan sizing.
• Not an air purifier, though the filtration in the unit helps with what comes in from outside. See do air purifiers work.

Do you need one?

Probably yes if: the house is new or has been thoroughly air sealed, you get window condensation in winter, odours linger, or the air feels stale.

Probably not yet if: the house is older and leaky. Do the air sealing and insulation first — that's where the energy return is — and add ventilation as the house gets tight. Assess the whole picture with the home energy score calculator.

The bottom line

Both units recover heat from the air you exhaust; only the ERV also moves moisture. Choose the HRV when the problem is too much indoor humidity — typically cold climates with well-occupied houses — and the ERV when you want to limit incoming humidity in a humid summer or retain scarce moisture in a dry winter. Size to the applicable ventilation standard, check the cold-climate defrost strategy, keep the kitchen exhaust separate, and clean the filters and core on schedule or the whole thing quietly stops working.

Start with how to air seal a house — sealing comes first, ventilation follows.

Standards and code reference

The standards behind this guide, for looking up in the edition your jurisdiction has adopted:

• ASHRAE 62.2 — whole-house mechanical ventilation rates
• IRC M1505 — ventilation system requirements

Code editions and local amendments vary. Confirm the adopted edition with your AHJ, and treat manufacturer instructions as governing wherever they are more restrictive.