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What an HRV Saves in a Cold Climate
An HRV pulls stale indoor air out and fresh outdoor air in, and passes both through a core where heat moves from the warm stream to the cold one without the air mixing. The calculator answers one question: how much of the heat that ventilation air would otherwise need does the core give back, and what is that worth over a heating season.
The Heat Recovery Math
The supply air leaves the core at the outdoor temperature plus the efficiency times the gap between indoor and outdoor. At 21 °C indoors, a -23 °C design temperature and 70% sensible efficiency, the supply air is -23 + 0.7 × 44 = 7.8 °C. Without recovery, 45 L/s of air needs 0.045 m³/s × 1.2 kg/m³ × 1.006 kJ/kg·K × 44 K = 2.39 kW of heat. With the HRV the same air needs 0.72 kW, a drop of 1.67 kW. The efficiency is a single number here. A real core loses ground in deep cold and often runs a defrost or frost control cycle in deep cold, so treat the design-day result as a best case.
From Degree Days to Dollars
Heating degree days count how far and how long the outdoor temperature sits below 18 °C. Multiplying the heat saved per degree (1.67 kW ÷ 44 K = 0.038 kW per °C) by 4,000 degree days and 24 hours gives about 3,650 kWh of heat per year. A 92% efficient gas furnace burning gas at 10.42 kWh per m³, a heat content taken from Statistics Canada's 37.5 MJ per m³, needs 381 m³ less gas, worth $114 a year at $0.30 per m³. The calculation assumes the HRV runs at the full rate all year. Use the degree day calculator if you want the degree days for another base temperature.
Choosing a Design Temperature
The design temperature sets the peak load and the design-day supply temperature, and it does not change the annual saving, which comes from the degree days. Take it from the climatic data for building design in Appendix C of the National Building Code. The free BC Building Code Appendix C, Table C-2 lists the January 1% and 2.5% temperatures and the degree days for each BC location. Vancouver City Hall, for instance, is -7 °C at 2.5%, -9 °C at 1% and 2,825 degree days. The presets above give degree days from the 2020 NBC. They do not set a design temperature, because the value depends on your location and on whether you use the 1% or 2.5% basis.
What Efficiency to Enter
Efficiency is tested to CSA C439 at 0 °C and -25 °C. Under the ENERGY STAR specification for HRVs and ERVs, a certified unit needs at least 65% sensible recovery at 0 °C and 60% at -25 °C, with a minimum fan efficacy of 1.2 CFM per watt when the efficiency is below 75%. Version 2.4 of the specification lifts the 0 °C requirement to 75% from 1 January 2028. Because the figure falls as the air gets colder, an annual estimate is better served by a value between the two ratings than by the 0 °C headline number.
Fan Electricity and Payback
An HRV runs two fans all year. At 95 CFM and the ENERGY STAR minimum of 1.2 CFM per watt, the fans draw about 79 W, which is 696 kWh and $97 a year at $0.14 per kWh. Against the $114 of gas saved, that leaves about $17, and an exhaust-only system would also run a fan, so this net figure is on the low side. Savings grow with colder climates, higher airflow and costlier fuel. The HVAC payback calculator turns a net saving and an installed cost into a payback period. A home that needs mechanical ventilation anyway should judge an HRV on comfort, moisture control and the incremental cost over a plain exhaust fan, not on the gross heating saving alone.
HRV or ERV
An HRV recovers sensible heat only, so the moisture in the exhaust air leaves the house in winter. That suits a tight home that runs humid. An ERV also moves part of the moisture across the core, which holds humidity indoors in winter and keeps some outdoor moisture out in a humid summer. The ERV calculator runs the same comparison for energy recovery.
Frequently Asked Questions
An HRV preheats incoming air with the heat in the exhaust, so it removes a share of the ventilation heating load equal to its sensible recovery efficiency. A 45 L/s (95 CFM) system at 70% efficiency, 21 °C indoors and a -23 °C design temperature warms the supply air to 7.8 °C and cuts the ventilation load from 2.39 kW to 0.72 kW. Over 4,000 heating degree days that is about 3,650 kWh of heat, or $114 a year with a 92% efficient gas furnace at $0.30 per m³. The fans use about $97 of electricity at $0.14 per kWh, so the net saving is smaller than the gross figure.
Start from the ventilation rate your code requires. ASHRAE 62.2 gives 0.03 × floor area (ft²) + 7.5 × (bedrooms + 1) CFM, which is 90 CFM (42 L/s) for a 2,000 ft², 3-bedroom home. The National Building Code sets its own principal ventilation capacity in Section 9.32, and the table depends on the edition your province adopted. Then pick a unit whose certified airflow at your duct system's static pressure covers that rate, not the free-air maximum on the box.
Use the manufacturer's certified value, which is tested to CSA C439 at 0 °C and -25 °C. ENERGY STAR currently requires at least 65% at 0 °C and 60% at -25 °C, and Version 2.4 of the specification raises the 0 °C figure to 75% from 1 January 2028. Efficiency falls as it gets colder, so for an annual estimate enter a value between the two ratings, and for a design-day supply temperature enter the -25 °C value.
An HRV recovers sensible heat only, so the moisture in exhaust air leaves the house in winter, which helps a tight home that runs humid. An ERV also moves part of the moisture across the core, which holds more humidity indoors in winter and keeps some outdoor moisture out in a humid summer. The ERV calculator compares the two, and the better choice depends on whether your home runs too humid or too dry through the heating season.