Let's take a standard 2kW (2000 watt) heater as our baseline for this discussion. Over the course of one hour, it will use two "units" of power (costing 50-60c) to produce two "units" of heat. Got the physics? Now, on to the language.
Efficiency is recognised as the ability to reduce waste, save effort or energy, or generally to accomplish more by using less.
For example, an energy efficient lightbulb produces the same amount of light while using less power. Similarly, a fuel-efficient vehicle travels 100km on fewer litres of petrol than an inefficient vehicle.
In most cases, efficiency is a matter of relativity. In other words, one thing is seen as efficient relative to something else that is inefficient. Here is the kicker for today's discussion: all plug-in electric heaters are considered inefficient when compared with heat pumps, wood burners and flued mains gas heaters. By comparison, heat pumps have an efficiency of 1:3 or 1:4. This means that for one unit of power they produce three or four units of heat.
From this perspective, the claims above appear completely out of line. Let's start with the last one: "Outstanding energy efficiency." Shocking claim. I suggest this squarely falls into the category of false advertising. Sadly, it probably works brilliantly and has resulted in many sales to well-meaning people.
Next up: "Only 400 watts." This gets to the heart of the e/eco/econo/ecocalifragilisticexpialidocious claims on certain plug-in electric heaters. They are small and give off little heat. When compared to a 2000 watt plug-in heater, a 400 watt heater uses one-fifth of the power and generates one-fifth of the heat. In both cases the efficiency ratio is 1:1.
Imagine you pull into a petrol station and the offer of the day is one-fifth of tank of petrol for only one-fifth of the price of a full tank. Is that a bargain? Which brings us to another claim: "Save up to 50% or more on your heating costs." According to my calculations, if you replace every 2000-watt heater in your home with a 400-watt heater you will save exactly 80 per cent on your heating costs because you will live in a very cold home.
I could go on all day but it appears I've run out of words, so I'll leave you with this: "Whole room heater." Absolutely true for a small room or a very warm day.
The lesson is to be cautious of all claims on how to make your home warmer and drier.
Seek independent expert advice from the EECA Energywise website (www.energywise.govt.nz) or the Eco Design Advisors website (www.ecodesignadvisor.org.nz). Or submit your questions to: House Calls, c/o Anna Wallis, Deputy Editor of the Chronicle.
