HRV, DVS and Smartvent Running Costs in NZ Winter 2026: Are These Systems Actually Saving You Money?

If you've got an HRV, DVS, Smartvent or Lossnay system humming away in your roof space, you've almost certainly asked the question this month: with Contact lifting daily charges from 1 May, Genesis raising retail prices an average of 12.8% from 16 May, and Meridian warning of up to 7%, is it time to switch the thing off and save the power?

Short answer: for most homes, no — and switching it off blindly often costs more than running it. But the right answer depends on which system you've got, what mode it's in, when you bought it, and whether it actually has heat recovery or is just a fan blowing roof air into your hallway. This piece runs the real numbers for the systems most NZ homes actually have, against the new winter 2026 tariffs, and gives you a tighter operating playbook before June bites.

At a Glance

How much electricity these systems actually use

Ventilation systems are sold as "uses less than a lightbulb." That's roughly true for the smallest positive-pressure units and very wrong for the larger balanced heat-recovery models that have two fans, sensors, dampers and sometimes a built-in heater.

Here are the realistic average draws for the units we see in NZ homes most often:

Two patterns matter here. First, positive-pressure systems have one fan and tend to cycle on and off based on humidity or schedule, so they're not actually running flat-out for 24 hours. Second, balanced heat-recovery systems run two fans (one extracting stale air, one bringing fresh air in through the heat exchanger) and are designed to run continuously — that's how the heat recovery works. So the wattage looks higher because it is higher.

What the new May 2026 tariffs mean in dollars

We've worked the running cost two ways: a flat-rate plan at 35c/kWh (a fair national post-hike average) and an off-peak-friendly plan at 22c/kWh weighted average (closer to what an EV-tariff or time-of-use plan looks like).

Positive-pressure system, 30W average, 12 hrs/day:

• Annual energy: 30W × 12h × 365 = 131 kWh
• At 35c/kWh: $46/year
• At 22c/kWh: $29/year

Heat-recovery balanced system, 90W average, 24 hrs/day:

• Annual energy: 90W × 24h × 365 = 788 kWh
• At 35c/kWh: $276/year
• At 22c/kWh: $173/year

Big balanced HRV with built-in pre-heater (Lossnay LGH-50 with heater on):

• Energy can climb to 1,400–2,000 kWh/year if the resistive pre-heater is engaging on cold nights
• At 35c/kWh: $490–$700/year
• This is the case where the running-cost question gets serious — see the section on settings below

So the answer to "does it cost much to run?" is genuinely "depends on which system." A 1990s positive-pressure unit on a sensible schedule is rounding-error territory. A modern balanced HRV with the pre-heater engaging through a Wellington or Dunedin winter is a real line item.

The "I'll just turn it off to save money" trap

This is the question most people are actually asking. It feels obvious: if the unit costs $200 a year to run, switching it off saves $200. Right?

Almost never. Here's what happens instead in a typical NZ home that switches its ventilation off on 1 June:

1. Indoor humidity climbs from 50–60% to 70–80% within a week. Cooking, showering and breathing add 8–10 litres of moisture per day with nowhere to go.
2. Damp air is genuinely harder to heat. Water vapour absorbs energy. Your heat pump or fixed heater works longer to hit the same room temperature. Most NZ homeowners report 10–15% higher heating bills with the windows shut and the ventilation off.
3. People reach for the dehumidifier. A typical 20L domestic dehumidifier draws 300–500W and runs 6–10 hours a day in a damp NZ winter. That's $90–$200 a winter, dwarfing what the ventilation system was using.
4. Condensation reappears, mould follows in 4–6 weeks. Cleaning, repainting, or treating mould-affected ceilings and walls is a real cost most insurance won't touch.

The honest maths: switching off an $80/year positive-pressure unit and replacing it with a dehumidifier and harder-working heat pump usually costs you $150–$300 more across the winter than just leaving the ventilation on. For balanced heat-recovery units, the gap is bigger — those systems are actively recovering heat that would otherwise leave with the stale air, so switching them off forfeits the recovery as well as creating the moisture problem. We covered the diagnostic side of this in how to stop window condensation in NZ homes for winter 2026; this is the running-cost flipside.

Heat recovery: how it pays for itself (or doesn't)

The thing that makes a balanced HRV system different from a positive-pressure one isn't just the second fan — it's the heat exchanger sitting between them. Outgoing warm, stale air passes through one side; incoming fresh outdoor air passes through the other. The exchanger transfers 60–80% of the heat from one stream to the other without mixing the airflows.

In practice, that means the air your heat pump or fixed heater is warming has already been pre-warmed by the ventilation system. The numbers from EECA modelling and Consumer NZ testing land in roughly the same place: a balanced heat-recovery system in a typical NZ winter offsets $150–$400 a year in heating that would otherwise be lost to ventilation.

So for a Lossnay-style system that costs $200 a year to run and saves $300 a year in heating losses, the net is about $100/year in your pocket — which doesn't pay back the $5,000–$8,000 install cost over its life, but means the running-cost question is the wrong one. It's already paying for itself in operating terms.

For a positive-pressure system with no heat exchanger, the maths are different. The system pulls outdoor (or roof-space) air, which in a Dunedin July is bitter cold, and pushes it into your hallway. Your heating system then has to warm that air. The unit doesn't recover anything — it just moves moisture out and cold air in. The benefit is moisture control, not heating efficiency. We unpack the system-choice trade-off properly in positive pressure vs balanced ventilation.

Five settings that quietly double your running cost

If you're going to leave the system on through winter, the easiest 30 minutes of work you'll do this month is checking these settings. We see at least three of them wrong in most homes we visit.

1. Summer profile left on through winter. Most modern HRVs ship with seasonal modes. Summer mode runs the fan slower and uses cooler outdoor air to chill the house at night. Winter mode runs the fan harder to handle higher indoor humidity and engages heat recovery. If you've never touched the settings, you're probably on whatever the installer left it on years ago. Change it.

2. Humidity setpoint too low. The default 50% target was fine in 2015 when power cost less. At today's tariffs, a 55–60% indoor humidity setpoint cuts run-time meaningfully without any noticeable difference in comfort. Below 50% the system runs constantly chasing a target you don't actually need.

3. Pre-heater (booster heater) left on auto. Mid-range and large Lossnay units have a small resistive heater that warms incoming air on very cold mornings. It's an efficiency comfort feature, not a heating solution — and in some installs it's left on through autumn and spring when it's not needed. A 1.5kW pre-heater running 4 hours a day on cold mornings is $300+ a winter on its own. Set it to engage only below 4°C outdoor, or turn it off entirely if your home isn't drafty.

4. Boost mode forgotten. "Boost" or "party mode" runs both fans flat-out for fast humidity recovery — useful after a hot shower or a roast dinner. It's also what the kids accidentally pressed last weekend and never turned off. Check the controller.

5. Filters that haven't been changed since 2024. A clogged filter forces the motor to work harder for the same airflow. You can lose 20–30% of efficiency and add real wattage to the motor draw before you notice anything. Filters are $30–$80 a pop and most balanced systems need both an intake and extract filter changed twice a year.

When it IS genuinely OK to turn the unit off

There are a handful of situations where switching off saves money without backfiring:

• Mild dry days when windows are open anyway. A clear October Saturday with the kitchen door open does the ventilation job for free.
• Holidays. Empty house, no moisture being produced. Switch it off (but consider leaving it on a low-fan timer if you're away for more than a fortnight to keep the air moving and prevent stagnation smells).
• Unused bedrooms. Close the diffuser to that room rather than turning the whole system off — this directs the same airflow to occupied spaces.
• Spring and autumn shoulder months. September and April in most of NZ don't need the system running 24/7. A 6-hour overnight schedule is plenty.

What you should not do: switch it off in May or June because you've heard about power prices going up. The whole point of the system is to manage the moisture that builds up exactly when the windows close for winter.

Pre-winter service checklist (before June)

Before the first really cold week, walk through this list. None of it is hard, and it'll keep your running cost where it should be:

1. Replace the filters. Both sides on a balanced system. Note the date on the housing with a marker pen.
2. Clear the roof intake. A leaf blocking the cowl is the most common cause of unexplained run-time increases. Five-minute job with a torch.
3. Listen to the fan. A new bearing-noise rattle means the motor is on its way out. Replacement is $300–$600; ignored, it usually fails in mid-winter.
4. Check humidity sensor calibration. If the controller reads 45% and your kitchen feels muggy, the sensor is drifting. Most installers will recalibrate during a service visit.
5. Inspect the roof space for damp. This matters more for positive-pressure systems. Wet insulation, mould on rafters or visible water staining means the system is making your problem worse, not better — get it assessed before winter properly bites.
6. Book a service if it's been more than two years. A professional service runs $150–$250 and includes filter changes, sensor checks, fan testing and diffuser cleaning. On a balanced system that's running 24/7, it pays for itself in efficiency.

The bottom line

For most NZ homes with an HRV, DVS, Smartvent, Lossnay or similar system, the answer to "should I turn it off to save money this winter" is: don't, and instead spend half an hour fixing your settings.

A positive-pressure unit on a sensible schedule costs $30–$80 a year to run on the new tariffs. A balanced heat-recovery system costs $150–$300 to run but offsets at least that much in lost heating. Switching either off and trying to manage winter moisture with a closed-up house and a dehumidifier almost always costs more — and adds the slow tax of mould creeping back into the corners of bedrooms.

If your system is more than 10 years old, hasn't been serviced in three winters, or is a positive-pressure unit drawing from a damp roof space, the question is a different one — and worth getting a fresh assessment on. Take our 2-minute home energy assessment to figure out whether your current setup is the right one for your home, or find ventilation installers in your area for a service quote before winter. For the bigger picture on what ventilation actually fixes in NZ homes, our complete home ventilation guide is the place to start.