By Adel Majd, Chief ExtraOrdinary Officer, Air Force Shield (how we write). Published in HVAC Maintenance & Efficiency
A heat recovery ventilator, or HRV, brings fresh outdoor air into a tightly built house and exhausts stale indoor air, passing the two streams through a core that transfers heat from one to the other. Most newer GTA homes have one because modern construction is too airtight to ventilate itself. The filters need cleaning every two to three months, the core and condensate drain at least once a year, and a full service that includes the ducts and hoods is a $90 add-on to an Air Force Shield duct cleaning.
What an HRV or ERV does
Older houses leak. Air moves in around windows, through the attic hatch and up the chimney, and that leakage, unintended as it was, kept indoor air changing over. Houses built in the last few decades are sealed far better, with house wrap, taped sheathing, spray foam and tight windows. That saves energy, but it means moisture from showers and cooking, carbon dioxide from the occupants, and off-gassing from furniture and finishes all stay inside unless something moves them out.
An HRV is that something. Canada Mortgage and Housing Corporation's HRV maintenance guide describes it in one line: a heat recovery ventilator brings fresh air into your home without losing heat. Two fans run inside a cabinet the size of a small suitcase, usually in the basement or a mechanical room. One fan pulls stale air from the bathrooms and kitchen and pushes it outside. The other pulls fresh air in from outside and delivers it to the bedrooms and living areas, or into the furnace return so it is distributed with the heating system. Between the two fans is the core, a block of thin plates through which the streams pass side by side without mixing. In winter the warm outgoing air heats the cold incoming air. In summer, with the air conditioning on, it works the other way.
An ERV, or energy recovery ventilator, is the same machine with a core that transfers moisture as well as heat. In a humid Toronto summer an ERV keeps some of the outdoor moisture out, and in a dry winter it keeps some indoor moisture in. For cleaning purposes the two are handled the same way, with one difference covered below.
Why most newer GTA homes have one
Subdivision houses built in Vaughan, Markham, Oakville, Milton, Brampton and across the outer GTA in recent decades are usually tight enough that the builder installed mechanical ventilation. In most of them that is an HRV, and in a growing number of newer builds an ERV. If your house is a newer build and you have never looked, check the basement for a cabinet with four large ducts attached and two hooded vents on an outside wall near it. That is the unit. Condo suites in some newer towers have a compact in-suite version.
Many homeowners inherit an HRV with the house and never touch it. The Lifebreath owner's manual states that several maintenance procedures are required to keep the HRV in good working order, and CMHC notes that most new HRVs are designed to run continuously. The most common thing we find is a unit that has been running continuously for years with its original filters.
The parts that need attention
The core
The heat exchange core is the heart of the unit. Every litre of air entering or leaving the house passes through it, and dust from both streams settles on the plates. A dirty core moves less air and transfers less heat. HRV cores are usually aluminium or plastic and can be washed. ERV cores are made of a moisture-permeable material and must not be soaked, only vacuumed, so it matters which one you have.
The filters
There are two, one on each airstream, sitting against the core. On most residential units they are washable foam or mesh. They are the first line of defence for the core and they load up fastest. Clogged filters are the usual reason an HRV seems to have stopped doing anything.
The intake and exhaust hood screens
The two outside hoods have a wire mesh to keep out birds and insects. The intake screen catches cottonwood fluff, grass clippings, leaves and in winter frost and snow. A blocked intake starves the house of fresh air and throws the unit out of balance.
The condensate drain
In winter the warm exhaust air condenses on the cold core, and the water runs to a pan at the bottom of the cabinet and out through a small tube to a floor drain. If the tube kinks or the trap blocks, water sits in the pan, and a musty smell from the fresh-air grilles follows.
Balancing
The two airstreams are supposed to move equal volumes. If the intake side is restricted the house goes slightly negative, pulling air in through every gap; if the exhaust side is restricted it goes positive, pushing moist indoor air into the walls. Dirty filters, a dirty core and a blocked hood all unbalance the unit. After a cleaning the unit should be checked for balance, which is done with the dampers on the two ducts and a flow gauge.
How often each part needs service
Intervals vary by manufacturer and by how dusty the house is. The two sources we trust most for a GTA home are CMHC and the Lifebreath owner's manual, since Lifebreath is one of the brands we see most often in local subdivisions.
| Component | CMHC guidance | Lifebreath Series HRV manual |
|---|---|---|
| Exterior hoods | Clear leaves and debris; clear snow and frost in winter | Inspect monthly |
| Filters | Clean or replace every 2 months | Clean quarterly |
| Core | Vacuum and wash per the owner's manual | Clean every two years |
| Condensate drain | Pour about 2 litres of warm water through each pan until it flows freely | Inspect and flush annually |
| Ductwork | Inspect once a year; vacuum inside the duct ends | Wipe and vacuum once a year |
Sources: CMHC's How to Maintain a Heat Recovery Ventilator and the Lifebreath Series HRV owner's manual, Table 4.1. Lifebreath lists the core interval as "biennially"; some of its other product manuals give shorter intervals, so follow the manual for your model. CMHC adds that if a more thorough cleaning is required, call your HRV service technician.
In practice, a homeowner who rinses the filters every season and checks the hoods when cutting the grass will keep the unit working. The core, the drain, the ducts and the balance are the parts that get skipped, and those are what a professional service is for. Once a year is the right interval for that if the unit runs continuously, and every two years is acceptable in a house with no pets and little dust.
What our HRV cleaning involves
On a house visit the HRV is a $90 add-on to the duct cleaning. The technician will:
- Switch the unit off at its disconnect and open the cabinet.
- Remove the filters and the core. Wash HRV filters and cores in warm soapy water, no bleach or pressure washer, as the manufacturers specify. Vacuum ERV cores rather than wash them.
- Vacuum the inside of the cabinet, the fan blades and the drain pan.
- Flush the condensate line and check the trap.
- Clean the two outside hoods and their screens.
- Clean the HRV's own supply and exhaust duct runs with the compressed-air tools and vacuum already on site for the furnace ducts.
- Reassemble, restart and confirm airflow at both hoods.
Full details are on the HRV cleaning page. Book two $90 add-ons and the third is free, so a house that also needs the dryer vent and the humidifier done pays for two.
Where we see the most HRVs
The subdivisions in Vaughan, Markham and Oakville built over the last two decades are where HRVs are nearly universal, and they are where we most often find a unit that has run for years on its original filters. Richmond Hill, Milton, Brampton, Ajax and Whitby are similar. Older Toronto neighbourhoods rarely have one unless the house was gutted and rebuilt.
If you are booking a duct cleaning for a newer house, mention the HRV when you book. Pricing for the cleaning itself by home size, along with every add-on, is on the cost page. Call (416) 548-7833 seven days a week, 6:00 AM to midnight.
Frequently Asked Questions
How often should an HRV be cleaned?
CMHC says to clean or replace the filters every two months. The Lifebreath owner's manual says filters quarterly, the condensate drain annually and the core every two years. A professional service once a year covers the core, drain, hoods and ducts.
Should my HRV run all the time?
Yes. CMHC notes that most new HRVs are designed to run continuously. A tight house needs the air exchange year-round, and the unit only recovers heat while it is running.
What is the difference between an HRV and an ERV?
An HRV transfers heat between the outgoing and incoming air. An ERV transfers moisture as well. ERV cores must be vacuumed, not washed.
How much does HRV cleaning cost?
It is a $90 add-on to an Air Force Shield duct cleaning, before HST. Book two add-ons and the third is free.
Why does my HRV smell musty?
Usually a blocked condensate drain with water standing in the pan, or a core that has not been cleaned. Flushing the drain and washing the core resolves it.
Can I clean the HRV myself?
Filters and hoods, yes, and CMHC's guide walks through it. The core, the drain line, the duct runs and balancing the unit are the parts most people leave to a technician.
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