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4) Ask a contractor.
Most furnace professionals give free in-home estimates for in-
stalling new heating equipment during which they will recom-
mend a unit size. A contractor familiar with the homes in your
neighborhood will likely be able to give you an idea of what
size you might need. Keep in mind that while a contractor’s
opinion is valuable, it is just that – an opinion – unless he per-
forms a heat load calculation.
5) If you are replacing an existing furnace, look at
what size you have.
If the unit you have now is the correct size for your home,
replace it with the same size. How do you know what size you
currently have? Look at the name plate on the furnace usually
located somewhere inside the unit (remove service panel to
nd). Remember, you want to look at the “output” BTUs here.
Newer furnaces are higher eciency, meaning for every input
BTU, you get more output BTUs (heat) in your home. Therefore
a new furnace will be smaller (a lower input BTU rating) than
your existing furnace.
Replacing a furnace with the same size one might work if you
have lived in the home long enough to go though a winter
season and decide that it is operating properly. However, if
you’ve added insulation or upgraded your windows, a smaller
furnace may be needed. On the other hand, if you’ve expanded
the home, a larger furnace may be needed.
Depending on the type of furnace you’re shopping for, there
are only a few sizes to choose from which move in about 20,000
BTU increments. So while the sizing process might involve a bit
of educated guesswork, since there are only few sizes to choose
from, the likelihood of getting the right size furnace is actually
very good. Also, if you are shopping for a gas or propane forced
air furnace, you might want to select what’s called a two-stage
furnace. A two-stage furnace is actually two furnace sizes
combined into one unit, so using one of these furnaces means
it covers a wider spread of sizing capabilities.
Efficiency
The next thing to do is choose what eciency you want for
the equipment. This is a personal choice, based on how much
money you want to save on your fuel or electric bill when oper-
ating the heater.
Heaters that operate on gas, oil or propane have dierent
eciency ratings which are indicated as an AFUE percentage
(Annual Fuel Utilization Eciency), and indicated as a HSPF
number (Heating Season Performance Factor) on electric heat
pumps. The higher the AFUE percentage or HSPF rating the
more ecient the unit. Higher eciency equipment produces
the same amount of heat as lower eciency units of the same
output BTU size; the dierence is that higher eciency heaters
use less fuel or energy to do so, thereby saving you money on
your utility bills.
Heaters that are 20+ years old usually have eciencies of 65%
to 70%. Old heat pumps usually have HSPF ratings of 5 or 6.
This equipment costs a lot of money to operate compared to
new equipment.
New boilers and forced air gas furnaces have eciency ranges
starting at 80% up to 95+% (also called “direct vent” heaters).
There is also a bonus if you buy a heater that is 95% eciency
or higher: the Federal government gives a $150 - $200 rebate
for this equipment purchased in 2007. Each percentage of
increase in equipment eciency means the same decrease in
your monthly fuel bill. For example, let’s say you have an old
propane furnace that is 65% ecient, and your current gas
bill is $200/month in the winter. If you replace it with a 95%
propane furnace, you will see a 30% savings (95 minus 65). That
means your new propane bill monthly would be $140, or a
$70/month savings.
Heat pumps (and air conditioners) are rated for their cooling ef-
ciency by SEER (Seasonal Energy Eciency Ratio). The higher
the SEER, the less electricity used to create the same amount of
cooling. New heat pumps have eciency ratings from 13 SEER
up to 16 SEER. Each additional SEER rating equals about 7%
savings on your electric bill. More good news: the Federal gov-
ernment gives a $300 rebate for buying a heat pump in 2007
that is 15 SEER or higher.
A high eciency heater is a particularly good idea if:
You live in central or northern USA•
You plan on staying in your home for more than 4 years•
You want to help preserve the environment by using •
less electricity
To help with your decision from a nancial perspective, you can
use this Equipment Efficiency Comparison Calculator to see
how much money you might save in operating costs by com-
paring dierent eciency units for your particular home.
Comfort Features
The primary goal of a heater is to keep you warm, and the
measurement of that is if your home is the temperature that
you set your thermostat for. If you set your thermostat for 72
degrees, and the furnace achieves 72 degrees, the furnace has
accomplished its primary comfort function. Besides this basic
functionality on forced air furnaces there are only about two
real comfort feature options.