Heat recovery: cutting the energy bill

Why heat recovery matters in a commercial building

In a commercial or institutional building, heating and cooling are a heavy share of energy use — often the dominant line on the bill. A large part of that energy is used only once before being thrown away: exhaust air pushed outside is warm in winter, and a boiler’s combustion gases leave the stack still carrying plenty of heat. Heat recovery captures part of that already-paid-for energy and puts it back to work instead of letting it escape outdoors.

For a building manager, it’s one of the few levers that lowers spending without degrading comfort or operations. The principle is simple; the value lies in sizing, in integration with existing systems, and in maintenance over time.

Recovering on ventilation: HRVs and ERVs

Every occupied building must bring in fresh air. In winter that means exhausting tempered indoor air and pulling in frigid outdoor air that then has to be reheated. A recovery ventilator passes both streams through an exchanger: outgoing air gives up its heat to incoming air without the two mixing.

There are two families:

• The HRV (heat recovery ventilator) transfers only sensible heat — temperature. It’s a good fit when the main load to recover is thermal.
• The ERV (energy recovery ventilator) also transfers part of the moisture. It helps manage indoor humidity: limiting dryness in winter and reducing the moisture load in summer.

The choice between the two isn’t about brand but about the building’s profile: occupancy, internal humidity loads, process type, air-quality requirements. In Québec, the length and severity of the heating season make the temperature gap between exhaust and fresh air especially favourable for recovery: it’s precisely when it’s coldest outside that there is the most to recover.

On performance, units certified ENERGY STAR by Natural Resources Canada must reach a sensible heat-recovery efficiency (SRE) of at least 65% at 0 °C and 60% at −25 °C. That’s a useful benchmark for comparing equipment, but real-world performance depends on airflow, filter maintenance and system balancing.

Recovering on combustion: the boiler economizer

A natural-gas boiler sends its combustion gases up the stack at a still-high temperature. An economizer is a heat exchanger installed in the flue that transfers part of that heat to the boiler’s feedwater — or to another useful fluid on site.

Natural Resources Canada distinguishes two types:

• The non-condensing economizer, the most common, keeps the gases above their dew point to avoid corroding the ductwork. It typically raises overall efficiency by 2% to 4%.
• The condensing economizer drops the gas temperature below the dew point and captures much more heat; it can improve boiler efficiency by 10% to 15%, provided there is a low-temperature heat sink able to absorb that energy (cold make-up water, a low-temperature return loop, domestic-water preheating, and so on).

These figures are orders of magnitude established by NRCan, not a performance guarantee for a given site. The real benefit depends on the boiler’s operating regime, the gas temperature, the draft, and whether there is a use able to make value out of the low-temperature recovered heat. That’s exactly what a field study validates before any work is committed.

Cost, timelines and what makes it pay off

Heat recovery isn’t a single product but a family of solutions, from a ventilation recovery unit to a waste-heat recovery loop between processes. Cost and timeline therefore vary widely with the scope of the work and the state of the existing systems.

Three factors drive payback more than the equipment’s purchase price:

1. Operating hours. A system running continuously recovers far more than an intermittent one. Buildings with long occupancy (institutions, multi-residential, some retail) are the most favourable.
2. The available temperature gap. The hotter the rejected source relative to what you want to preheat, the larger the gain. Québec’s climate works in favour of ventilation recovery here.
3. A use for the recovered heat. Recovering heat is pointless if there’s nothing to preheat at the right moment. Integration with the existing system is the heart of the project.

The right move isn’t to compare spec sheets, but to start from an audit: where the heat goes, in what quantity, at what temperature, and what on site could use it.

Funding: Québec programs

Several Québec programs support energy-efficiency projects that include heat recovery. Hydro-Québec funds the installation of efficient equipment and systems in commercial, institutional and industrial buildings through its Solutions program, and Énergir offers financial help for energy-efficient renovation and new-construction projects aimed at cutting natural-gas use.

Terms, ceilings and eligibility conditions change from year to year, so the applicable program and its requirements should be confirmed before locking the design. A well-built file — baseline measurements, estimated savings, eligible equipment — makes the incentive easier to secure and protects the return on investment.

Where to start

Heat recovery is rarely a purchase; it’s an engineering decision. Before choosing equipment, you have to map the building’s heat rejections, identify the uses able to absorb recovered heat, and verify compatibility with the existing ventilation and boiler room.

Montréal Combustion works across Greater Montréal, the North Shore and the South Shore to assess a building’s recovery potential, size the solution to real usage, and connect the project to the applicable incentive programs — so the energy you’ve already paid for works for the building instead of leaving through the roof.