Space Heater Efficiency
The Dollar Stretcher
by Gary Foreman
Hi Gary,
Here's a heating question. I'm someone who really likes to be warm. If you can
believe it, I grew up in a house that was kept at 75 degrees in the winter. I'm
trying to adjust to a cooler house as an adult but it's not easy! Anyway, here's
the question. Which is more efficient, using my electric space heater/fan which
requires about 1000-1500 watts, or turning up my relatively new, gas-powered,
forced air furnace to heat up a good sized two bedroom apartment? I've already
done as much insulating as I can. I'd really appreciate it if you could help me
figure this out! Connie
As someone who's lived in Florida for years I can appreciate Connie's desire to
keep warm! At the same time it's also important to find ways to do that without
watching your energy bills go through the roof. Her inclination is right. As a
general rule, if you're only going to be in one room it will be cheaper to heat
that single room than the whole apartment. And a space heater is often a good
choice.
First, some warnings. Electric space heaters can overload an electrical circuit.
Be careful to avoid problems. No matter what type of heater you use remember to
take all appropriate safety measures. Proper inspection and use are important.
Protect your family from shocks, fires and asphyxiation. Safety should always
come first.
Next, let's look at Connie's comparison. Unfortunately, getting an exact answer
isn't easy.
To figure out the cost of operating a space heater you need to multiply the kilowatts
used per hour times the cost per kilowatt hour for electricity. Multiply that
by the length of time that the heater is actually on. You can get the kilowatt
hours by dividing the wattage by 1,000. Your electric bill should show you how
much you pay per kilowatt hour.
Electric space heaters do not lose any energy through ducts or combustion. So
they're considered to be 100% efficient. All of the warmth generated by the space
heater will radiate into the room.
Here's where it gets more difficult. To know how much it costs to operate her
gas furnace she'd need to know how energy efficient the furnace is. Most convert
between 55 and 85% of the gas used into actual heat. She'd also need to know the
furnace's rate of fuel consumption and the cost of fuel in her area.
If that wasn't enough Connie would also need to account for the loss of heat in
her ducts. Depending on the insulation and condition of the ducts she could be
losing a major portion of the heat generated by the furnace before it gets to
the rooms.
Finally, she'd need to convert both the space and central heaters to a common
measure of heat. The most likely candidate is BTUs. And, there's no easy way to
do that for either of the two heaters.
But that doesn't mean that some comparisons can't be drawn. The U.S. Dept. of
Energy estimated that an average conventional gas system cost 43% as much as a
space heater when heating a whole house. So on average the gas central system
is more efficient.
No, she shouldn't throw out the space heater. Let's keep it in perspective. It
still makes sense for Connie to use the space heaters to boost the temperature
in one or two rooms of her home. And not knowing the exact cost shouldn't keep
her from getting the most heat for her dollar. Her strategy is fairly simple.
Her first step should be to lower the thermostat for the central gas system to
the lowest comfortable level. If she's only using one or two rooms, she should
lower it some more and use space heaters to warm up the room she's using.
Connie can also manage something called her 'thermal comfort'. What's that? In
it's simplest form it means that the coldest part of your body will determine
how cold you feel. Proper management of thermal comfort could allow her to lower
the thermostat by 8 degrees without feeling any colder. And that could save 15%
of her heating bill.
So Connie will want to eliminate drafts and places where her skin is
exposed to the cold. It turns out that Mom was right. You should wear warm stocks
and a turtle neck sweater in winter!
Connie has already taken steps to add insulation. Another possibility is to add
weather-stripping. In many homes if you add up all the cracks it's as if a window
were left wide open letting out heat all winter long. Not only that, the cold
air coming in lowers the thermal comfort.
Connie's well on her way to getting the most for heating dollar this
winter. All she needs now is a cup of hot chocolate!
Gary Foreman is a former Certified Financial Planner
who currently edits The Dollar Stretcher website.
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