A home without central ducts: the ventilation puzzle we solve most often in Lachine
Projects in this area almost always begin the same way: a homeowner calls us because they had a wall-mounted heat pump installed the previous year, are delighted with it, and have just realized something no one explained to them at the time of purchase. A wall-mounted heat pump heats, cools, and slightly dehumidifies—but it does not bring in a single cubic foot of outdoor air. It simply circulates the air already inside the house.
In this postwar bungalow located just minutes from the Lachine Canal, the results were visible to the naked eye in February: condensation at the bottom of the living room windows, swelling bathroom baseboards, and a finished basement that held on to the smell of Thursday night's dinner until Saturday. The owner had bought a portable dehumidifier, then an air purifier. Neither changed anything, for one simple reason: neither one brings fresh air into the house.
What was missing was an air exchanger. At AirGreen, we installed a compact FANTECH FLEX 100H HRV with top-mounted connections, suspended by chains above the basement water heater, with a fully dedicated duct network.
The context: why this project was anything but ordinary
The house had no central air distribution. It originally had electric baseboard heating, followed by the addition of two wall-mounted heads whose copper refrigerant line runs through the basement joists—visible in our jobsite photos, just above the unit. There was therefore no return duct into which to inject fresh air, no plenum, and no central fan to interlock.
This scenario represents a significant share of our calls in Lachine, Verdun, the Southwest, and the older neighborhoods of Montreal: fully electric homes with no duct network, where adding an air exchanger requires building the entire system from scratch. It involves more work than connecting to a central system, but technically, it is also the best of the three possible configurations.
Fully dedicated installation: what it changes in practice
The manufacturer describes three ways to connect an HRV: simplified installation (exhaust into the return, supply a few feet downstream), partially dedicated installation (dedicated exhaust, supply into the return), and fully dedicated installation.
In a fully dedicated installation, the unit has its own network, independent of any heating or cooling system:
- Exhaust grilles placed where the air quality deteriorates—bathrooms, kitchen, basement, laundry room;
- Supply registers placed where people live and sleep—bedrooms, living room, dining room;
- no dependence on a third-party fan, so no electrical interlock is required.
The advantages are real and measurable: air delivery is precise, balancing is easy to achieve, and the unit ventilates 24 hours a day without another system needing to run in parallel. In a home without central ducts, it is not really a choice: it is the only practical option.
Why the FLEX 100H instead of a larger unit
This is where an installer's judgment matters more than the catalog. The basement mechanical room was just over one meter wide, squeezed between the foundation wall, the water heater, and a storage door that still had to open fully. Clear height below the joists was barely 7 feet.
The FLEX 100H met these constraints:
- Dimensions: 17 7/8 in. high × 21 1/2 in. wide × 14 1/2 in. deep. It is one of the most compact HRVs in FANTECH's residential catalog, and the six-inch height difference compared with a standard-size unit literally determined whether installation above the water heater was feasible.
- Weight: 39 lb, allowing suspension from the joists with chains without structural reinforcement.
- Airflow: 49 to 104 CFM at 0.4 in. w.g., exactly the useful range for a roughly 1,400-square-foot, three-bedroom home.
- 5-inch oval connections on top, a format that gains height where a 6-inch round collar no longer fits.
- Recirculation defrosting, rather than stopping the supply fan.
Recirculation defrosting, simply explained
When outdoor air drops below approximately -5°C, moisture in the stale air passing through the core can freeze. FANTECH offers two strategies to prevent this.
The supply fan shutdown temporarily cuts off the intake of fresh air and lets the home's warm air thaw the core. It is simple and robust, but during this cycle, the house is placed under slight negative pressure.
Recirculation defrost instead circulates indoor air in a loop through the unit to thaw the core without unbalancing the house. The manufacturer describes it as the most energy-efficient mechanism and recommends it for cold or humid outdoor conditions—two words that aptly describe a January near Lac Saint-Louis. It also limits stagnant air that contributes to indoor condensation in winter, which was precisely the initial symptom in this house.
The deliberate trade-off in energy consumption
We prefer to say it plainly, because this is the kind of detail that technical specifications bury: the FLEX 100H consumes 89 W at low speed and 172 W at high speed, for a ventilation efficiency of 0.6 cu. ft./min per watt. This is not the best figure in the range—electronically commutated motor units perform three to five times better. In return, they are taller, wider, and heavier.
In this house, the mechanical room settled the debate. We compensated by programming the unit to run continuously at low speed rather than in full-power cycles, and by assigning the peaks to bathroom timers that return the unit to its normal speed after 20, 40, or 60 minutes. When the available space dictates the model, we adjust the control strategy, not the physics.
The installation process
The suspension: four chains, not two straps
The unit is suspended by four chains secured to the joists, one at each corner, with hooks facing inward. This detail matters to us. We regularly see, on service calls in Laval and on the North Shore, HRVs screwed directly beneath the joists or held up by two plumber's straps. The first setup transmits every fan vibration into the bedroom floor above. The second eventually deforms and leaves the cabinet cantilevered, which throws the access door out of alignment and lets stale air leak into the mechanical room.
We also leave sufficient clearance at the front to open the door fully and remove the core: two latches beneath the cabinet, and a core that can be removed in one motion, without dismantling the ductwork.
The ductwork
The system was installed with rigid galvanized ducts wherever possible, using oval-to-round transitions at the unit collars, and insulated flex duct only for the final few feet, pulled as tight as possible. Flex duct snaking between the joists means lost airflow at every bend.
Two aluminum wall hoods were installed through the side wall: fresh-air intake on one side, stale-air exhaust on the other, spaced far enough apart to prevent the unit from drawing back in what it has just expelled, and mounted high enough to remain clear after normal snow accumulation. Both exterior ducts were insulated and fitted with a vapor barrier all the way to the unit.
The condensate drain above a water heater
A site-specific point to watch: the unit is located directly above a water heater. The condensate drain was therefore routed with a clear slope and a trap, away from the tank's piping and fittings, all the way to the floor drain. We tested the circuit with water before leaving the site. An HRV drain without a trap draws air through the pipe and brings drain odors back into the house; a drain dripping onto a water heater accelerates corrosion on top of the tank.
Balancing with a manometer
The step that almost no one bills for, and that we do systematically. The FLEX 100H door has a printed balancing table: it relates the airflow, in cubic feet per minute, to the pressure measured at the unit's two test ports—one for supply and one for exhaust. We connect a manometer to each port, read the pressure, compare it with the table, and adjust the dampers until the two airflows match.
An HRV that is unbalanced on the exhaust side puts the house under negative pressure and draws air in through the crawl space, the drain, and around the windows. When unbalanced on the supply side, it pushes humid air into the walls. The table is printed on the unit door for a reason. It is rarely used.
Two days of work, one technician and one apprentice, with the entire system installed.
What a homeowner should check before signing an HRV quotation
- Is the proposed configuration named? Simplified, partially dedicated, fully dedicated: these three words must appear in the quotation. If they are not there, the system was not properly designed.
- Is the defrost type indicated? Recirculation or fan shutdown, according to the planned connection.
- Is balancing included and documented? Ask for the final airflow readings in writing.
- Is access for maintenance preserved? A unit installed three inches from a wall will never be cleaned.
- Are the exterior hoods positioned and spaced properly? If they are too close together, they short-circuit each other; if they are too low, they disappear under the snow.
Grants and certification
The Québec government's Rénoclimat program provides assistance of $500 for installing or replacing an HRV or ERV, provided that the unit is certified by the Home Ventilating Institute (HVI) and an energy evaluation is conducted before and after the work. The initial evaluation must take place before the project begins; retroactive applications are not accepted. Program requirements change from year to year, and we encourage every customer to verify the current conditions before scheduling the work.
ERV maintenance in practice
- Every three months: remove the filters, rinse them with warm water, and let them dry completely before putting them back.
- Once a year: remove the core, vacuum it, wash it with warm soapy water, and check the drain trap.
- Twice a year: clear the exterior hood grilles, which are often clogged with dryer lint and plant debris.
Regular HVAC maintenance makes the difference between a unit that lasts fifteen years and one that only ventilates at half capacity by its third year.
AirGreen in Lachine and Greater Montreal
Our teams serve Lachine, Saint-Pierre, LaSalle, Dorval, and the entire West Island, as well as Montreal, Laval, Longueuil, the North Shore, and the South Shore. We install air exchangers, wall-mounted heat pumps, central systems, and residential ventilation solutions, and we document every HVAC installation before leaving the premises.
If your home has no central ducts, if your windows sweat in January, or if your current air exchanger has never been balanced, write to us. We assess the mechanical room, tell you frankly what will and will not fit, and provide a quote with the ductwork configuration clearly written out.