Flued gas heaters

Performance

We assessed the Energysavers in an expanded version of the thermal comfort laboratory we use to test electric heaters — 5m wide by 6m deep and with a 2.4m-high insulated ceiling. Both heaters are floor-mounted units and, like heat pumps, are costly to shift once installed.

We fitted them halfway along a wall. After stabilising the lab’s temperature at 8°C, we cranked the heater’s thermostat to maximum and started timing.

Heat-up time: In just over 5 minutes, the 559FT raised the temperature by 5°C, and within half an hour had our lab at a balmy 23°C. This excellent result wasn’t surprising as the 5.3kW unit is designed to heat rooms as large as 82m². Its performance is comparable to a similar-sized heat pump. The 309FT, which has a lower heat output (3.1kW), took nearly 10 minutes to achieve a 5°C temperature rise and only increased the temperature to 16°C after half an hour.

Evenness: Both gas heaters warmed the room as evenly as a heat pump would, with just over 1°C variation between the warmest and coldest parts of the room.

The experience: Heat pumps and gas heaters warm through convection, using a fan to circulate warm air, rather than by radiating heat directly at you, like a woodburner or bar heater. However, a heat pump can take a while to get going, especially as the outdoor temperature falls (in the same way your car’s heater blows chilly air for the first few minutes on cold mornings).

In contrast, the Energysavers instantly produce a jet of hot air. Consumers who are frustrated their heat pumps emit a type of heat that’s too “soft” are likely to prefer the instant, powerful heat of a gas convector.

Noise: We measured the sound levels of the Rinnai heaters and found them slightly quieter than heat pumps, though there’s still a perceptible fan noise throughout the room.

Ease of use

How easy heat pumps are to use is a major drawcard. Push a button on a remote and within minutes your home is cosy. Bells and whistles such as timers and WiFi control further automate the heating process. How do gas heaters compare? (Note: the Rinnai Energysaver 559FT and 309FT have the same control panel).

Starting: Both gas heaters have an instant electronic start we found reliable.

Controls: The Energysavers have a push-button digital control panel, allowing you to set the thermostat (16-26°C), select an “economy” mode, activate a child lock or operate the timer. There’s also an indicator light showing when you need to remove and clean the filter. We found the controls easy to understand and use. There’s no remote, so you have to wander over to the heater every time you need to make an adjustment. The electronic controls and starting mechanism mean the heater needs a mains connection, and won’t work in a power cut.

Changing the dust filter: The filter is readily accessible from the top of the heater and easy to remove, clean with a vacuum and replace.

Timer: The Energysavers feature dual timers. You can set each timer to provide 2 periods of heating each day. Setting the timers is simple.

Overall, they’re as easy to use as heat pumps, but the lack of a remote is frustrating.

Economics

If you’re already hooked up to natural gas and paying fixed daily charges for powering your water heater and cooktop, you should get your money’s worth by using gas to keep warm as well.

A heat pump with the same capacity as the Rinnais costs about the same to buy and install. While electricity costs more than gas per unit, heat pumps convert every unit of power into 3 or more units of warmth.

In terms of overall running costs, heat pumps are generally cheaper to run. That said, gas prices vary by region which can change the equation.

The Energysaver heaters can also be powered by 45kg LPG cylinders. That means isolated properties and houses in the South Island can run them as well. However, the much higher cost of LPG makes them miles more expensive to run.

Safety

The Rinnai Energysaver gas heaters we tested are flued models, meaning they have a pipe that serves as a chimney for emissions and airborne moisture. Their external temperatures remain low making them much safer than radiant heaters, especially if there are kids around. They also have a child lock for the controls. Overall, they’re as safe as heat pumps.

Unflued portable gas heaters are to blame for the reputation of gas heating as a hazardous way to keep warm. They’re dangerous to use unless the room is well-ventilated, as they remove oxygen from the air and can produce carbon monoxide if there’s a fault. Even worse is they fill the air with moisture, contributing to dampness and mould. Don’t buy them.

The bottom line

Both Rinnai Energysavers are good heaters: they can be cheap to run, heat up quickly and evenly and are easy to use. As the 559FT has a significantly higher heat output than the 309FT, at a similar upfront cost, we think it’s the better option for homes needing to heat a decent-sized living area.

However, the low running cost of heat pumps, combined with their comparable purchase price and the range of models (which means you can find one for nearly every size living area), means they are the better option for most of us. That said, the Rinnai Energysaver 559FT can be a good bet if you tick the following 3 boxes:

• You get cheap per-unit rates for natural gas and already pay for a connection.
• You have a decent-sized living area to heat (but not larger than 82m² ).
• You want guaranteed instant heat even on the coldest mornings.

The future of gas

It’s no secret natural gas is a depleting resource. Not only that, burning it is bad for the environment.

There’ve been calls for banning new gas connections from 2025 and gas prices are only projected to rise. At the same time the gas industry is touting biogas and hydrogen as the saviour of the industry. This technology is still in its infancy and is no way guaranteed.

In our view, the only thing you can be sure of is natural gas is more of a gamble than electricity. That said, large increases in natural gas prices in the short term are unlikely.