Choose an ERV in a humid climate and an HRV in a cold dry one. The difference is whether the unit transfers moisture as well as heat.
Older houses ventilated themselves whether anyone wanted it or not. Air leaked through window frames, floorboards, chimneys and a hundred unsealed penetrations, and it carried moisture out continuously at the cost of a large heating bill.
Sealing that up saves real energy and removes the accidental drying with it. This is why damp problems so reliably appear in the winter after new windows go in — nothing got wetter, the leaks that were quietly removing moisture were closed.
- HRV heat recovery
- 60–85%
- ERV moisture transfer
- 50–70%
- Typical whole-house rate
- 0.35 ACH
- Filter service
- 3–6 months
Of the heat that would otherwise leave with the stale air
Why it suits humid climates
Air changes per hour — the usual design target
Neglected filters are the main cause of underperformance
What the units actually do
An HRV (heat recovery ventilator) runs two airstreams past each other through a heat exchanger: stale air leaving, fresh air arriving. It recovers most of the heat from the outgoing air without mixing the streams, so you get continuous fresh air at a fraction of the heating penalty. It transfers heat only — the moisture in the outgoing air leaves with it.
An ERV (energy recovery ventilator) does the same and additionally transfers some moisture between the streams. In summer that means incoming humid air gives up part of its moisture to the drier outgoing stream, so it arrives less humid. In winter it means some of your indoor moisture is retained rather than exhausted, which in a very dry climate is a benefit and in a damp one is not.
A PIV (positive input ventilation) unit takes a different approach: it gently pressurizes the house with filtered air from the attic or outside, pushing stale moist air out through the remaining leaks. It is common in the UK, less so in the US, and it is simpler and cheaper than a full HRV — but it recovers no heat and it only works on a house with somewhere for the air to go.
| System | Recovers | Best for | Verdict |
|---|---|---|---|
| HRV | Heat | Cold, dry winters | Midwest, Northeast, Mountain |
| ERV | Heat and some moisture | Humid summers | Southeast, Gulf, Mid-Atlantic |
| PIV | Nothing | A leaky house with a damp problem | Cheap, effective, no heat recovery |
| Exhaust-only fan on a timer | Nothing | Simple retrofit | Works; costs heat |
| Trickle vents | Nothing | Background air in a sealed window | Better than nothing, weather-dependent |
| Opening windows | Nothing | Free, when the outdoor air is drier | Still the first move |
When it does not work
The limits matter more than the benefits — this is where most money gets wasted.
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It is not a dehumidifier
Ventilation exchanges your air for outdoor air. If the outdoor air is more humid than yours, even an ERV brings moisture in — less of it, but still some. In a humid summer you need dehumidification as well.
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It only pays back in a tight house
Installing an HRV in a drafty building means recovering heat from air that is also leaking out of every other opening. Air sealing comes first, then ventilation.
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Neglected filters undo it
These are the most set-and-forget systems in a house, and the most degraded by it. Filters and cores need servicing on a schedule or the airflow quietly falls away.
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It cannot fix a localized cold spot
Whole-house ventilation lowers whole-house humidity. A specific corner that keeps growing mold is a surface temperature problem regardless of how well the house breathes.
Doing it properly
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Confirm the house is actually tight
New build, recent window replacement, or a retrofit with air sealing. In an older leaky house, ventilation is rarely the missing piece.
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Do the free things first
Extraction, habits and purge ventilation. A whole-house system is an expensive way to solve a problem that indoor laundry was causing.
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Pick the type from your climate
ERV where summers are humid, HRV where winters are cold and dry. In a mixed climate, weigh which season causes you more trouble.
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Size it to the house, not the room
Around 0.35 air changes per hour is the usual design target. This is a calculation worth having done properly rather than estimated.
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Plan the duct routes before buying
Extract from wet rooms, supply to living and sleeping rooms. Retrofitting ducting into a finished house is the expensive part.
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Commission it and measure
A system installed and never balanced often moves far less air than specified. Ask for measured flow rates at the terminals.
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Put the servicing in the calendar
Filters every three to six months, core cleaned annually. This is what decides whether it still works in year five.
What it costs
Prices are US retail ranges in 2026 and running costs assume roughly 16 cents per kWh. Treat them as the shape of the decision rather than a quote.
| System | Installed | To run | What it suits |
|---|---|---|---|
| Exhaust-only (continuous fan) | $400–$900 | $3–$8/mo | Simplest and cheapest; no heat recovery |
| Supply-only with filter | $700–$1,500 | $4–$10/mo | Pressurizes the house slightly; keeps dust out |
| HRV (heat recovery) | $1,800–$4,000 | $6–$14/mo | Recovers heat, not moisture — the cold-climate choice |
| ERV (energy recovery) | $2,200–$5,000 | $6–$16/mo | Recovers heat and some moisture — humid and mixed climates |
| Positive input ventilation unit | $600–$1,400 | $3–$7/mo | Attic-mounted, common retrofit for whole-house condensation |
How to tell it is working
A whole-house system is judged on consistency rather than on any single reading. Before commissioning, log the morning humidity in three rooms for a week — the worst room, an ordinary bedroom, and the living room. After commissioning, do it again. The result you are looking for is that the spread between the three narrows: the point of these systems is that no room is left behind, not that the average drops dramatically.
The second measure is how quickly the house recovers from an event. Run a bath, cook a meal, dry a load of laundry indoors, and watch how long the elevated reading persists. A commissioned system should return the house to baseline within an hour or two without anybody opening a window.
The most common disappointment has nothing to do with the unit. Systems get installed at a commissioning flow rate and then turned down to their quietest setting by whoever lives with the noise, at which point they move too little air to do the job. If a system stops performing months after installation, check what setting it is actually running at before diagnosing anything else.
What to check before you commit
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Pick the type from your climate, not the brochure
HRV recovers heat and dumps moisture, which is what a cold dry winter wants. ERV recovers some moisture too, which helps in a humid summer and stops a very cold climate from getting uncomfortably dry. Fitting the wrong one gives you a working machine solving the wrong problem.
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Ask for commissioning figures in writing
A system is designed around a flow rate. Without a commissioning sheet you have no way to tell whether it was ever set up correctly or whether it drifted, and no basis for a complaint if it underperforms.
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Check where the ducts run
Uninsulated ducting through a cold attic condenses internally and can deliver water into ceilings. It is the single most common installation defect on retrofit systems.
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Solve the moisture sources first
These systems are sized for a normal household load. An unvented clothes dryer or laundry dried indoors every day will keep a correctly specified system permanently at its limit, and the fix costs a fraction as much.
Common mistakes
Buying an ERV for a cold dry climate
It retains moisture you wanted to lose in summer and does not help in winter dryness the way people expect. Match the unit to the season that troubles you.
Installing before air sealing
You end up recovering heat from a fraction of the air actually leaving the building.
Treating it as a dehumidifier
On a humid August day it brings in humid air, however efficiently. It is fresh air with heat recovery, not moisture removal.
Never touching the filters
The most common reason a system that worked at handover does nothing five years later.
Common questions
What is the difference between an HRV and an ERV?
Both exchange stale indoor air for fresh outdoor air while recovering most of the heat. An ERV also transfers some moisture between the airstreams, so incoming summer air arrives drier — which makes it the better choice in a humid climate.
Do I need whole-house ventilation?
If the house is new or recently air-sealed and humidity stays high despite good habits and working exhaust fans, yes. In an older leaky house it is rarely the missing piece.
Why did my house get damp after new windows?
The old windows were ventilating the house continuously through their leaks. Replacing them removed that accidental drying without replacing it with anything — which is what trickle vents or mechanical ventilation are for.
Can an HRV replace a dehumidifier?
Not in a humid climate. It brings in outdoor air, and if that air is more humid than yours it raises indoor humidity. The two do different jobs and a humid summer often needs both.
Will whole-house ventilation make my heating bills worse?
Exhaust-only and supply-only systems do add to the heating load, because they replace warm air with cold. Heat-recovery systems return most of that heat — commonly 70 to 90% of it — so the net cost is the fan power plus a modest heating penalty. In a leaky older house the honest answer is that a system often changes where the air comes in more than how much of it there is.
Is a positive input ventilation unit worth it for condensation?
In the right house, yes. It works by gently pressurizing the building with filtered attic air so that damp indoor air is pushed out through gaps rather than sitting against cold surfaces, and it is a cheap retrofit that has a good record against whole-house condensation. It is the wrong tool where the attic air is itself damp, where the house is very airtight, or where the underlying problem is a leak.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions