Ontario's Plain-English Guide to Custom Home Buildingπ 705-533-1633 | βοΈ 1-866-868-6606 | βοΈ info@icfhome.ca
HRV and ERV Balancing and Maintenance: The Flow Hood, Frost Protection, Cold Drafts, Cores, Filters, the Condensate Drain and the Twice-a-Year Check
Heating, Cooling & Ventilation
Balancing and Looking After an HRV: Twenty Minutes Twice a Year, One Proper Visit With a Flow Hood, and the Drain Line That Freezes When Nobody Is Watching
An HRV is about the lowest-maintenance machine in the house, which is exactly why most of them are never maintained. The filters plug, the core fills with dust, the fans end up moving half what they did on day one, and the owner decides HRVs do not work. They work fine. They need to be balanced once, properly, by somebody with the right instrument, and then cleaned twice a year by you. This page covers both, plus the two winter complaints I hear most: frost and cold drafts.
What It Costs to Keep One Running
| Item | Who does it | How often | Cost |
|---|---|---|---|
| Balancing with a flow hood | Technician | At commissioning, and after any duct or hood change | $200 to $400 |
| Core cleaning and filters | Homeowner | Twice a year | your time |
| Replacement filters, where the unit uses them | Homeowner | As the manual says | $30 to $80 a set |
| Furnace or heat pump service, for comparison | Technician | Once a year | $150 to $250 |
| HRV or ERV retrofit, if it is starting over | Contractor | Once | $2,500 to $5,000 |
Two filter sets a year at $30 to $80 is $60 to $160 a year, or $600 to $1,600 over ten years. Many units have washable filters and the cost is a bathtub and a bit of patience. The install itself is priced on the HRV installation cost page.
Why Ontario prices are all over the map: the contractors and price guides we checked for this page put the same HRV job anywhere from $1,500 to $3,250 for a basic GTA install to $2,000 to $4,000 whole house, and the ducts alone from $1,300 to $6,600. Balancing is one of the reasons. Some quotes include it with the readings written down, some include a fellow turning the knob until it sounds right, and some leave it out entirely. Budget $300 for balancing if the quote does not name it, and get two or three quotes on the same written scope.
Balancing Is Not Optional in a Tight House
Balanced means the HRV brings in about as much fresh air as it throws out. Unbalanced one way, it pressurizes the house and pushes warm, damp air into the walls and the attic. Unbalanced the other way, exhaust-heavy, it pulls the house negative, and a house under negative pressure gets its makeup air from wherever it can, including down the chimney of a natural-draft gas water heater. That is how a ventilation fan ends up putting combustion gas in the basement.
Balancing is done with a flow hood held over the grilles, or with a manometer across the test ports and the dampers built into the unit, and the readings go on a sheet that stays with the house. It takes a technician an hour or two. The knob on the wall control does not balance anything; it only turns the speed up or down.
Rule of thumb: supply and exhaust within about 10 percent of each other is what most installers aim for. If a gas appliance in the house is not sealed combustion, have a TSSA-registered gas contractor check its venting after the HRV is balanced, and keep a CO alarm on every floor.
Rebalance after anything that changes the ducts: a basement finished with new grilles, a kitchen renovation, a new range hood. The hood is a big enough subject to have its own page, range hood makeup air.
Frost, Defrost and the Drain Line
At minus 25 C, the warm, moist exhaust air passing through the core gives up its heat to the incoming air and drops its moisture as water, and in a cold enough core that water freezes. Every HRV sold for Canada has a defrost strategy: it stops bringing in outdoor air for a few minutes, or recirculates house air through the core, or preheats the incoming air. During defrost you may hear the fans change and the unit seems to stop breathing. That is normal. A unit that never defrosts at minus 25 C is broken; a unit that defrosts all day is usually out of balance or has a plugged core.
The meltwater leaves through the condensate drain, a small hose with a trap in it running to a floor drain or a pump. This is the part that goes wrong. A kinked hose, a trap that dried out in summer, or a line run across a cold garage wall freezes or backs up, the drain pan overflows, and the first sign is a wet ceiling tile under the unit. Pour a cup of water into the pan each fall to prime the trap and watch it run out. ERVs make far less water than HRVs and some have no drain at all; the HRV vs ERV page covers why, and I will not re-explain it here.
Cold Drafts and Other Winter Complaints
The core warms the incoming air, but it does not make it room temperature. On a minus 25 C night the supply air comes into the bedroom noticeably cooler than the room, and a supply grille blowing straight down onto a bed or a reading chair feels like a window left open. The fix is where the grille is and which way it throws: high on a wall or in the ceiling, aimed along the ceiling, not at a person. Turning the HRV off fixes the draft and brings back the stale air, which is a cure worse than the cold.
Dry air in winter is the other complaint, and on an HRV running on high all January it is real. Turn it down to the rate the design called for, not higher. The longer story of winter humidity in a new house is on the humidity page.
The Twice-a-Year Check
- Unplug the unit first. It is a plug-in appliance with fans that start by themselves. This is the one machine in the mechanical room you are meant to open; a sealed combustion furnace, boiler or water heater is not, and that stays the gas technician’s job.
- Pull and wash the filters. Washable ones in warm water and mild soap, dried fully before they go back. Replace the disposable kind.
- Pull the core. Slide it out, rinse it gently in the tub with lukewarm water, let it drain and dry, and slide it back the right way round; there is usually an arrow. Do not use a pressure washer or hot water, and check your manual, because some ERV cores must never get wet.
- Prime and check the condensate drain. A cup of water into the pan, watch it run out, look along the hose for kinks.
- Go outside and clear the hoods. Bird nests, leaves, snow drifted against the intake, lint from the dryer vent next door. A blocked intake turns a balanced HRV into an exhaust fan.
- Look at the readings sheet. If the house has changed since it was balanced, book the $200 to $400 visit.
Spring and fall are the easy times to remember it: when the clocks change, the HRV gets its bath. My own record is not perfect. The core does not care what I meant to do.
Questions people ask
How often should an HRV be cleaned?
Core and filters twice a year, by the homeowner, spring and fall. Replacement filters, where the unit uses them, are $30 to $80 a set. Check the condensate drain and the outdoor hoods at the same time.
How do I know if my HRV is balanced?
Ask for the balancing sheet with the measured supply and exhaust airflows. If there is no sheet, it was probably not measured. Balancing with a flow hood is $200 to $400 and should be redone after any duct change or renovation.
Why does my HRV freeze up?
All HRVs make frost in the core in deep cold and are built to defrost. Repeated freezing usually means the unit is out of balance, the core or filters are plugged, the defrost setting is wrong, or the condensate drain is frozen. Clean it, prime the drain, then have it rebalanced if it keeps happening.
Why is cold air coming out of my HRV?
On a very cold night the supply air is warmed but still cooler than the room. A grille aimed at a bed or chair makes it feel like a draft. Move or redirect the grille rather than turning the unit off.
Should the HRV run all the time?
At the low, continuous rate the design called for, yes, with the bathroom boost for showers. Running it on high all winter dries the house and costs heat; running it off brings back the stale air and the window condensation.
Get the Ventilation Right in the Budget
The cost comparison calculator prices the same house five ways with the HRV in each one, so ventilation is in the number from the start instead of added at the end. If you have quotes that mention an HRV but say nothing about balancing, the $99 review reads up to three and points out which one left it out.
Sources and further reading
- What is a heat or energy recovery ventilator and why do I need one?: Natural Resources Canada: HRVs and ERVs in plain language, and why an airtight house needs one.
- HRAI consumer information: the Heating, Refrigeration and Air Conditioning Institute of Canada: what to ask an HVAC contractor and its member locator.
- TSSA: hire registered and certified fuels professionals: Technical Standards and Safety Authority: why gas furnace, boiler and water heater work must be done by a registered contractor with a certified technician, and how to check.
