Portable home heating usually means portable electric heaters. While convenient, these invariably ‘burn’ electricity derived from precious fossil fuels. Their initial cost may be low but running costs can be high.
In this Portable Home heating guide, we look at three things
Types of heaters
Where to use them
Efficiency – power use to heat a specified area
We don’t cover furnace, forced air systems, boiler/radiator, heat pumps, ducted air-conditioning, underfloor etc., as these require expensive capital outlays, installation and attention to thermal design. We also will leave gas heaters alone as they need a gas bottle or town gas connection.
A word first on thermal design
Good thermal design (also called passive design) means a home is cooler in summer and warmer in winter than the surrounding air. The nirvana is an 8-10° difference and to retain that cool/heat during the day or night.
A simple way to assess thermal efficiency is to compare the inside temperature to the outside. If it is less than 8° difference, you need to act. Done well, it can reduce heating or cooling costs by up to 40%.
The Australian Government has a great guide here, so here are a few points:
DIY Insulation in the form of fibreglass or aluminium, roof bats, or blow in composite reduces heat loss through the roof by 25-35%.
Window coverings – blinds and curtains reduce 10-20% heat leakage through glass
If you can get your thermals under control, it can mean only having to heat an area from 18° to 22° instead of 10°.
Portable home heating room size
It is essential to match the room size to the heater capacity.
Small bedroom 3 x 3 x 2.4m = 20m3
Medium bedroom 4 x 4 x 2.4 = 40m3
Large bedroom 5 x 5 x 2.4 = 60m3
Open plan kitchen, dining, lounge 5 x 10 x 2.4 = 120m3
As a guide, you need about 2000-2400W per 20m3 – the only issue is how fast you can raise the ambient heat load to achieve 22°.
Assuming electricity costs 30 cents per kilowatt-hour (kWh – number of watts per hour), that small, cheap, radiant bar heater will use 1800-2400W per hour – 55 cents to 72 cents per hour.
Heat the whole room or create a microclimate?
Most heaters radiate hot air that rises and cold air that falls – convection. The problem with convection is cold air from around the room is drawn into the convex. If you tried to heat the whole 120m3 open plan area, you would need six heaters strategically placed, chewing up big $$$ per hour.
Far more efficient are heaters that use fans and oscillation to create a heat zone or micro-climate. For example, the Dyson Hot/Cold fan and purifiers can heat a 45° cone-shaped area approx. 3 metres deep and 2 meters wide (15m2) while using a fraction of the electricity. They do it quickly as they don’t rely on convection. If you can reduce the area you need to heat, you will save significant dollars.
The Dyson Purifier Hot and Cool Model HP07 ($899) uses a 10-speed fan, variable oscillation angles and the Coandă effect (10x air multiplier) to blow air at up to 37°. It is perfect to quickly (10-15 minutes) create a microclimate around the lounge couch and then gradually (over a few hours) warm a larger area. Flat out – fan speed 10 and 37° it consumes <2000W. On auto fan and 22°, it uses from 500-1000W to maintain that microclimate. And you get air purification as a benefit.
The only other Coandă effect is the DeLonghi Air Purifier, Heater And Cooling Fan
Portable home heating – heater types.
No plug-in heater can heat more than a small 20m3 room, but the addition of a fan and thermostat may help heat a little faster.
And you need to know that these are hungry for electricity – most consume the same power as 24 x 100W light bulbs or 480 5W downlight LEDs.
These heaters are generally cheap and have a limited lifespan.
Running cost per hour
Radiant convention heater 2-bar typically <$30
Smaller closed rooms to 20m3
Radiant convention heater 3-bar typically <$60
Usually three settings 800/1600/2400
As above but the advantage of selecting lower heat levels
Ceramic heater with thermostat <$30
As above, but thermostat can save a few cents
Oscillating fan element heater with thermostat <$30
Tower fan heater with thermostat <$50
Convection heater with timer and thermostat <$60
Usually 2 settings from 1000/2000W
As above but the timer and thermostat may save money
Radiant ‘bathroom’ 1 or 2 bar strip heater <30
1200 or 2400W
Room size 10m3 When you are in a cold bathroom, running cost is not an issue
IXL-TASTIC heat lamp bathroom heater
Each lamp is 275W. Usually 2 or 4 lamp switchable
8 cents per lamp or 32c for four
Room size 10-20m3 As above, but as the heats radiates downwards, it can feel hotter.
In reality, these are no better than a radiant electric heater. But people believe they are more efficient – they are not and tend to be left on for far longer.
The heater works by convection. Oil is heated at the base and hot oil rises forcing colder oil to go to the base, etc.
But the catch 22 is that these take a very long time to reach operating heat.
This power rating will take about three times as long as a radiant heater
2400W usually with three settings – 800/1600/2400W
Heated throw rug
The solution uses a fraction of the power to heat you to just the temperature you want.
Typically 150W with 3 to 6 settings and auto-off
Space heaters (not portable – for comparison)
Space heaters are just a marketing term to make you think they are for larger spaces. The irony is that the maximum wattage you can plug into a power point is 2400 (240V/10A).
For example, Dimplex and others have electric faux wood fireplaces from about $2000 to $3000 with ratings from 1.0kW to 2kW – all capable of no more than 20m3. Some have a fan assist that can help to spread the heat. None have a remote thermostat because it would show how ineffective this was. Instead, they measure return or exit air.
You can get some with up to 3600W ($1.10 an hour) if these are wired into a 15W point. Some also work off three-phase and can consume up to 4500W ($1.35 per hour).
Wood fireplaces (not portable – for comparision)
Despite common belief, an open fireplace is one of the less efficient ways to heat a room. Why? A lot of heat disappears up the exhaust flue, and there is usually no way to move heat around a whole room – you may be snug in front of it but freezing three metres away. Not to mention the carbon and pollutants it can produce.
Air conditioning split systems (the best alternative to portable heaters)
The best way to heat (or cool) an area is to install a split system air conditioner. There are way too many brands and models, but the trick is to match the room size to the kW capacity (this is not electrical capacity but relates to BTU capacity) and then look for the most efficient models – usually the most expensive. These also have mandatory energy star ratings, so it is easy to choose. As a guide for a room (assumes 2.4m ceiling height)
The best thing about ACs is that they measure return air temperature and, when set to automatic, provide just enough heating (or cooling) to maintain that. Daikin has the Zena range of Coandă effect ACs that don’t blow on you but pick up to 10x times the air at the exit. These barely use .6kw at peak and over 8 hours average out at just over 30 cents in total. All plug into a 240V/10A/2400W socket.
What have you learnt about portable home heating? The prime take-home messages are
Address thermal design first to reduce the heat or cooling load from ambient temperature
Heat only the area you need – create micro-climates
Any radiant or oil heater that plugs into a 240V socket will not heat over 20m3.
Radiant heaters without a fan are the least efficient
Coandă effect fan heaters are the most efficient (cost far less to heat) but the most expensive to buy.
Finally, look at electricity cost over say 1000 hours.
That radiant 2-bar heater costs $720 – nearly twenty-four times its purchase price.
The Dyson HP07 costs $150, its purchase price is $899, but it pays for itself soon after.