Heating a rental cheaply: heat pump settings and what actually cuts the bill

What temperature should I set it to?

18°C is the World Health Organization’s minimum recommended indoor temperature for a healthy home. For living areas, most people find 18–20°C comfortable. Bedrooms can sit lower. Every degree above that costs real money — setting a heat pump to 25°C does not heat the room faster, the unit works at the same rate either way, it simply keeps running longer once the room is comfortable, and overshoots. If someone in the household is elderly, very young, or unwell, WHO guidance suggests a higher minimum, which is worth the extra cost.

Is it cheaper to leave a heat pump on all day?

It depends on how long you’re out. A heat pump is dramatically more efficient maintaining a temperature than recovering from cold. Bringing a chilled house back up takes a long, hard run at full output; holding it steady takes short, low-output cycles.

• Out for a few hours — leave it running at a lower setting, or turn it down rather than off
• Out all day, or away — turn it off, and use the timer to bring the house up before you return
• Overnight — most households do better turning it off in living areas, but in a poorly insulated house a low overnight setting may cost less than the morning recovery

The worse your insulation, the more the balance favours leaving it on.

Use heating mode, not auto

Auto mode is the single most common source of wasted money on a heat pump. In auto, the unit chooses between heating and cooling to hold a target temperature. On a variable New Zealand day it can end up cooling a room you are trying to heat — paying to remove warmth you paid to add. Select heat mode explicitly for the whole winter.

Point the louvres down

Warm air rises. With horizontal louvres, warm air collects at ceiling level, where the unit’s own sensor may read the room as warm while you are cold at floor level. Angle the louvres downward in heating mode. Set the fan to auto or high rather than low — running it on low for quietness slows circulation and leaves the room stratified.

Clean the filters

The highest-value maintenance task available to a tenant, and the most neglected. A clogged filter restricts airflow, making the unit run longer for the same result. Clean or rinse the indoor filters every two to four weeks during heavy use — slide the front panel open, remove the mesh filters, rinse in warm water, dry fully before refitting. Keep the outdoor unit clear of leaves, rubbish and vegetation — a blocked outdoor unit is the most common cause of a heat pump that “isn’t working properly.” If the unit ices up or blows cold air intermittently in very cold weather, it is likely running a defrost cycle, which is normal. Constantly, and it should be reported.

What your landlord has to provide

Under the Healthy Homes heating standard, your landlord must provide one or more fixed heaters that can directly heat the main living room, of an acceptable type, meeting a calculated minimum capacity for that room. So: a plug-in portable heater does not satisfy the standard, and neither does a heater that is present but undersized. Tenancy Services publishes a free Heating Assessment Tool that calculates the required capacity. If your living room never gets warm, run the numbers before concluding it’s your habits. The standard covers the main living room only.

The cheapest heaters to run, in order

• Heat pump — moves heat rather than generating it, delivering several units of heat per unit of electricity. Far and away the cheapest.
• Wood burner — cheap where you have dry wood; fuel cost varies enormously.
• Flued gas heater — moderate.
• Electric resistive heaters (fan, oil column, panel, bar) — all convert electricity to heat at essentially the same rate, so all cost roughly the same per unit of heat. An expensive oil column is not cheaper to run than a cheap fan heater. Fine for a short boost; expensive as a primary source.
• Unflued portable gas heater — avoid. Releases roughly a litre of water vapour per hour directly into your home, along with combustion products. A leading cause of damp and mould in New Zealand houses.

For dollar figures specific to your plan and region, use Powerswitch, run by Consumer NZ.

Free heat, and keeping it

• Open curtains during the day on sun-facing windows, and close them at dusk — before the room starts cooling, not at bedtime
• Lined or thermal curtains that reach the sill or floor and sit close to the glass make a substantial difference; a curtain stopping halfway down the window channels cold air into the room
• Close doors to contain heat in the rooms you’re using
• Block draughts at doors — and report obvious gaps or broken seals, because draught stopping is a Healthy Homes standard and unreasonable gaps are your landlord’s to fix
• Close off unused rooms entirely

If your bill is still high

Check whether you’re on the cheapest plan — switching retailers in New Zealand is straightforward, and Powerswitch compares plans free. Then check whether the property actually complies with the heating, insulation and draught stopping standards. A non-compliant house is expensive to heat by design, and that is not a problem you can solve with habits.

Frequently asked questions