Heat Pumps in Low-Energy Homes

Start with heat demand and system temperatures. An oversized heat pump may perform worse than equipment properly matched to the building.

Load before equipment

Calculate room loads at the design outdoor conditions. Floor area alone does not determine capacity.

System types

Air-to-water serves a hydronic system; air-to-air distributes heat through air; a ground source needs site and ground-loop assessment. Selection depends on distribution and available space.

COP and SCOP

COP refers to specified operating conditions; SCOP is a seasonal assessment under a defined method. An advertised number without conditions is not a bill forecast.

Supply temperature and hot water

Match emitters to the heat pump’s operating temperatures. Hot water has different timing and temperature requirements; check storage, reheating and priorities.

Backup and outages

Define operation in cold weather and during an outage. An electric backup heater can materially change backup-power requirements.

Oversizing and alternatives

Compare minimum modulation with low shoulder-season loads. For very low demand, evaluate simpler systems against capital cost, comfort and maintenance.

ZeroHouse assessment diagram; not a construction detail.

Project review matrix
Item	Parameter	Check / result
Building	Design load	Room losses
System	Supply temperature	Emitter selection
Backup	Peak electrical power	Outage scenario

What this means for your project

Compare quotations using the same conditions and explicitly stated electric backup. Avoid sizing based only on floor area.

Sources and scope of review

Checked: 2026-09-09. Editorial guidance; not evidence of compliance for an individual building.