Path-Q Solar
How does a ductless heat pump differ from electric resistance heating when sizing solar?
Answer
A ductless heat pump generally provides the same heating service with less electricity than resistance heating, but its actual demand depends on outdoor temperature, efficiency, sizing, controls, and backup operation. Solar sizing should use the specific system's expected seasonal electricity use rather than assuming the two technologies are equivalent.
Key points
- Resistance heating converts electricity directly to heat, while a heat pump moves heat and can deliver more heat per unit of electricity under suitable conditions.
- Heat-pump output and efficiency can decline in colder conditions.
- A heat pump may use resistance backup or supplemental heat during some conditions.
- Heating load timing is important because much winter demand may occur outside solar production hours.
What it depends on
- Heating load and building insulation
- Heat-pump capacity and performance across outdoor temperatures
- Use of supplemental or backup heat
- Climate and household temperature settings
Risks and trade-offs
- Using a simple efficiency assumption can understate cold-weather or backup demand.
- A heat pump may reduce annual electricity use relative to resistance heating but still increase winter peak demand.
- Solar production may be seasonally misaligned with heating consumption.
Information you may need
- Current heating electricity use
- Heat-pump model and performance data
- Backup heat type and controls
- Monthly heating demand and building conditions
Your next step
What to do next
Compare measured or estimated seasonal electricity use for the existing system with the proposed heat pump, including backup operation.
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