Will a heat pump keep up in a Greater Victoria winter?

What a marine winter does to a heat pump

The winter a heat pump sees here is weeks of wet air a few degrees above freezing, with a few days of outflow wind every couple of years that push the region to its design temperature. At zero to five degrees a modern unit is well inside its efficient range, so capacity is rarely the problem. Frost is. Near freezing, with our humidity, the outdoor coil pulls moisture out of the air as ice; the unit senses it, reverses briefly to warm the coil, and the ice melts and runs off, often with a puff of steam. For those minutes a ductless head goes quiet or blows cool, and a ducted system with electric strips may run them. In a damp December this can happen several times a day, and it is normal.

What the BC field study found

The best local evidence is the BC Cold Climate Heat Pump Field Study by RDH Building Science for BC Hydro and BC Housing, which monitored heat pumps in real BC homes through real winters, measuring what they delivered and consumed rather than what the ratings promised. In broad terms, units at the coastal, mild-winter sites delivered heating through the season at seasonal efficiencies that compare well with the colder Interior sites, and installation and control choices, including backup heat and setpoints, explained much of the gap between good and disappointing results. This page describes the study qualitatively on purpose; read it for its numbers.

Cold snaps and the −5 °C sizing rule

Outflow events are what people picture when they ask whether a heat pump will keep up: short, cold and dry, and what the rebate programs size to. The CleanBC whole-home rule requires the system to meet the full heating load at −5 °C with no electric resistance backup, using a NEEP-listed model and a CSA F280-12 calculation, which is why a whole-home system here is usually a cold-climate model at a premium of $1,500–$5,000our estimate (our estimate); the fall bonus, Level 1 / any-income examples — ductless-single: $1,000; ductless-multi: $1,000; central-ducted: $1,000, follows the same rules. Bigger is not safer: a unit oversized for the cold snap short-cycles through the other ninety-plus heating days. Ask for the heat-load printout and the unit's capacity at −5 °C rather than its nominal tonnage; the NEEP listing shows it.

Do you need backup heat, and what happens in a power outage?

Backup answers two questions: what covers the house if the heat pump alone cannot on the coldest day, and what heats it when the power is out. A whole-home cold-climate system sized at −5 °C answers the first with 'nothing is needed'; nothing electric answers the second. Most homes still keep something for the coldest day: bedroom baseboards set a few degrees below the heat pump; electric strips in a ducted air handler, allowed as supplemental under the electric-home rebate if the heat pump meets the full load; or a gas furnace kept as backup, a dual-fuel system at our estimate of $9,000–$16,000our estimate that changes which rebates are possible. A wood stove is accepted as backup by the income-tested program.

For the outage: a heat pump is off when the grid is off, and so is a gas furnace, because its blower and controls are electric. A gas fireplace with a standing pilot or battery ignition keeps working, as does a wood stove; a portable generator can run a single-zone ductless unit through an electrician-installed transfer switch, but not a central air handler with strips. The site has no verified local figure for a battery large enough to run a heat pump overnight.