Installation of a Lifebreath RNC 205 air exchanger in Boucherville

Three ways to connect an air exchanger to a home, and why the least expensive is rarely the right one

When a homeowner from Boucherville requests a quote for an air exchanger, they often receive three very different prices for what appears to be the same unit. The difference does not come from the brand or model. It comes from the connection method, and the manufacturer itself recognizes three of them. They do not produce the same results, they do not have the same code requirements, and one of them places a permanent constraint on the rest of the heating system.

The project described here involved a 1980s home in the eastern part of Boucherville, expanded at the rear with a finished basement. We replaced an undersized unit with a Lifebreath RNC 205, an ENERGY STAR-certified HRV with top-mounted ports—the blue sticker is visible at the bottom right of the door in the photo. The real work, however, was not suspending the cabinet. It was redoing a connection that should never have been installed the way it was.

The house: expanded by 45%, ventilated as before

This is a common sequence on the South Shore. An original home of approximately 1,500 sq. ft. A rear addition, with the basement converted into a family room with an additional bedroom and powder room. The living space increases by approximately 45%, the number of rooms to ventilate goes from six to nine—and the air exchanger, however, remains the one installed during construction.

The homeowners described to us exactly what this imbalance causes:

• the unit ran at high speed continuously, with the corresponding noise;
• the basement bedroom remained stuffy even in winter;
• condensation was accumulating on the upstairs bathroom window;
• the filters were clogging within six weeks.

An undersized unit does not compensate by working harder. It operates at its limit constantly, loses airflow as soon as the filters become loaded, and wears out its motors at the corresponding rate.

The three connection methods explained

The simplified method, known as return/return

It is the least expensive option, and it was the one installed in this house. Both connections on the house side of the air exchanger are tapped into the furnace return duct: stale air is drawn from the return, and fresh air is reinjected into it. There are no dedicated grilles anywhere in the house.

Its limitations are structural, and the manufacturer states them explicitly:

• balancing must be done at high speed, with the furnace fan running;
• it is mandatory for the furnace fan to run continuously, or for the HRV to be interlocked with the fan.

In practical terms, your heating system must circulate air continuously for your ventilation to exist. If the fan stops, fresh air enters a stationary return duct and goes nowhere. That is precisely what was happening here—the original installer had not installed an interlock, and the house was only actually ventilated when the furnace called for heat.

This method also affects the utility bill: running a furnace fan 24 hours a day often costs more than the air exchanger itself.

The partially dedicated system

An intermediate compromise, and often the best value for money in a home that already has a central duct system. Exhaust is dedicated: ducts go directly to the bathrooms and kitchen to remove stale air. Fresh air, meanwhile, is injected into the furnace's cold-air return, which distributes it.

The code distinction is important: unlike the simplified method, continuous fan operation or interlocking with the HRV is recommended here, not mandatory. Exhaust works regardless because it is independent.

The fully dedicated system

The air exchanger has its own duct network for both exhaust and supply: exhaust grilles in the bathrooms, kitchen, and laundry room, and supply grilles in the bedrooms, living room, and family room. It does not depend on the furnace.

This is the only possible method in a home heated by electric baseboards or a ductless wall-mounted heat pump without a duct network. It also offers the best room-by-room control. The manufacturer specifies a point we apply systematically: during balancing, all outdoor exhaust systems must be turned off—range hood, dryer, bathroom fans—because none of these appliances should draw their make-up air from the HRV.

In this Boucherville home, the furnace and its ductwork were in good condition and well balanced. We therefore chose a partially dedicated system: dedicated exhaust from the two bathrooms, the kitchen, and the new basement powder room; fresh-air supply connected to the return; and electrical interlocking of the furnace fan with HRV operation. The house is ventilated continuously without the central fan running unnecessarily all year.

The backdraft damper: the part almost no one installs

For all three methods, the manufacturer recommends installing a spring-loaded backdraft damper on the “stale air to outdoors” collar, with the blade hinge mounted vertically.

Its function is simple and often overlooked: when the HRV is on standby, turned off, or in recirculation mode, but the furnace or air handler is running, it can draw outdoor air through the heat exchanger's exhaust duct. The damper prevents this. Without it, the house gets an uncontrolled cold-air intake in the middle of January, exactly where no one thinks to look.

It is an inexpensive part. It is also one of the first things we check when a customer calls us because “there's a cold draft near the furnace.”

The RNC 205: more capacity, set lower

The RNC 205 is the highest-capacity residential top-port model in Lifebreath's RNC series. HVI-certified data:

• ASE (apparent sensible effectiveness): 79% at 65 CFM, at 0 °C
• SRE (sensible recovery efficiency): 71% at 64 CFM, at 0 °C
• SRE: 68% at 102 CFM, at -25 °C
• Power consumption: 64 W at low speed, 96 W at high speed, 1.4 A, 120 V
• Weight: 57 lb (25.8 kg) — dimensions: 33 5/8 x 18 3/4 x 15 in
• Removable and washable hexagonal counterflow HEX core
• Defrosting by recirculation damper, balancing dampers on all four collars
• ENERGY STAR qualified, CSA, HVI, ISO 9001, and HRAI certified

The sizing rationale

Many customers assume that a larger unit consumes more. At the same airflow, the opposite is true.

1. Noise. The sound level of a fan increases much faster than its airflow. An RNC 205 set to 120 CFM is inaudible from a bedroom; a small unit forced to 120 CFM is not.
2. Reserve capacity. The RNC 205 maintains 179 CFM at 0.4 in of static pressure. When the filters load up or a duct gets pinched, there is still some margin. A unit already operating at maximum has none.
3. Actual consumption. At 64 W on low speed over 8,760 hours per year, the unit costs less to operate continuously than a smaller model kept on high speed.

The continuous operating target selected for this house is around 120 CFM, established by adding the required airflow for each room according to the Quebec Construction Code, including the finished basement and bathrooms. The RNC 205 achieves this without leaving its intermediate speeds.

Execution details that determine the result

6 in outlets on a 5 in network

The RNC 205 uses 6 in (150 mm) oval collars. The existing network was 5 in. We made gradual transitions rather than fitting the outlets with an abrupt reducer: a restriction placed immediately at the unit's outlet creates turbulence where static pressure costs the most and cancels part of the benefit of the greater capacity.

The insulated flexible ducts visible in the photo are taut, supported, and straight for their first few feet. These three details, far more than the duct brand, determine the actual airflow measured at the grille.

Suspension and service clearance

The unit is suspended from the joists by the original straps and their S-hooks, visible on either side in the photo. At 57 lb, the load is modest; access is what matters. The manufacturer requires 25 in (635 mm) of clearance in front to remove the HEX core and filters through the two lower latches. In a finished basement, that clearance disappears within a season: a shelf, a freezer, winter tires. We mark it on the floor and record it on the commissioning sheet.

Condensate

The white braided hose with a red and blue stripe beneath the appliance is the condensate drain. The RNC 205 produces condensate during the cold season. Continuous slope, primed trap loop. A dry trap allows drain odors to rise into the cabinet, then into the distribution network—and the client then attributes the odor to the new appliance.

Terminations

• Exhaust: 10-002 kitchen grille with a washable grease filter, positioned away from the cooktop and never connected to the hood; 5-inch Techgrilles 99-EAG5 grilles in the bathrooms, on 99-TM5 connections.
• Exterior: 6-inch 99-186 high-density polyethylene caps with rodent screens, positioned away from the dryer outlet, plumbing vents, and the property line.
• Controls: 20/40/60 (99-DET01) timer in the main bathroom, wireless 99-DET02 version in the basement to avoid reopening a finished ceiling, 99-RX02 repeater if the range requires it.

Balancing, and the check that doesn't show up on the invoice

Each of the four collars on the RNC 205 has a balancing damper. We take digital manometer readings, adjust supply and exhaust to match, and record the values on the form provided to the owner.

With a partially dedicated connection, balancing is done with the furnace fan running, then checked with the fan off. This second reading is the one most often skipped, and it is the one that reveals whether the house becomes depressurized when the central system shuts down.

This point is not theoretical. The boxed warning on the appliance door is explicit: a ventilation system must never be installed in a situation where its normal operation, shutdown, or partial failure could cause combustion products from an appliance connected to a chimney to backdraft. In areas of Boucherville built between 1975 and 1995, gas fireplaces and chimney-vented water heaters are common. We inventory them before setting the airflow rates, and we measure the resulting negative pressure before leaving the job site.

We also verify the acceptability of the selected method and the placement of the exterior hoods with the appropriate authority: the manufacturer explicitly refers to local codes and regulations, which vary from one municipality to another on both the South Shore and the North Shore.

Grants: the amount—and the condition people forget

The Rénoclimat program provides $500 for the installation or replacement of a heat-recovery ventilation system. Two requirements apply to this amount.

The unit must appear in section 3 of the Home Ventilating Institute (HVI) certified product directory. The RNC 205 is HVI-certified, which we verify in the file.

After that, eligibility depends on an improvement in the EnerGuide rating between the pre-retrofit evaluation and the post-retrofit evaluation. Adding an HRV alone to an existing home increases energy consumption. Without energy-efficiency measures carried out as part of the same project, the rating may deteriorate and the grant may be refused—including for ventilation. The required sequence is therefore: pre-retrofit evaluation, then HVAC installation combined with insulation or air sealing, followed by a post-retrofit evaluation. We confirm this point with the program advisor before including it in a quote.

Maintenance: four steps that keep the numbers on track

1. Rinse the washable filters every two to three months.
2. Wash the HEX core once a year with lukewarm water.
3. Inspect the exterior hoods and backdraft damper in the spring.
4. Have the airflow readings taken again after any change to the duct network, any furnace replacement, or any installation of a central heat pump.

At AirGreen, we install, replace, balance, and maintain residential ventilation systems in Boucherville, Longueuil, throughout the South Shore, as well as in Montréal, Laval, and on the North Shore. If your home has been expanded or its basement finished since your heat recovery ventilator was installed, the unit has probably remained sized for the previous house. An airflow measurement confirms this in under an hour and will also tell you how your system is actually connected.