our opinions: ADVICE FROM AN EXPERT
In The
Comfort
Zone
In This Instance, Size DOES Matter
W
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hen you’re digging a hole to add a new plant to your
garden, the best tool for the job is probably a shovel. You
wouldn’t use a backhoe to add some petunias to your landscape.
In the same vein, you wouldn’t want to put in a 10-ton air-condi-
tioning unit when a two-ton unit is what your home really needs.
I know we live in Texas and we like everything bigger. I
know it’s hot. But one of the things we hear most when someone
calls needing a new unit is that “my current unit is not cooling
my house, so I need a bigger unit.” That may or may not be the
case. Last month I talked about all of the different reasons your
home may not be as cool as it was last summer. An improperly
designed duct system, leaking ducts, loose or poorly sealed
registers, or missing insulation can all make your system work
harder than it should. If you’ve called a reliable company and
had everything on your system checked and the result is that you
need a new unit, this is the time to make sure that the unit that
the company is recommending is the best one for your home.
I know it’s a big investment. A new unit can cost thousands,
even tens-of-thousands, depending on the size of your home.
And often homeowners want a larger unit than the one that they
are replacing, because the current unit is not cooling or heating
the house to their desired level of comfort.
It’s time to ask some questions of the installation company
when they tell you what size unit they recommend. The first one
is how they determined what size unit you need. Don’t be afraid,
there is math involved. The contractor should have used some-
thing called the “Manual J Load Calculation.” Luckily, as the
homeowner you don’t have to do the math, but you should make
sure that your contractor has. It is less work for the contractor
to guess at the size of the equipment than it is to do a proper
load calculation, according to Ron Therethy, author of This Old
House Heating and Cooling. An oversized system will heat and
cool, although it is not as efficient as a correctly sized one and
will not last as long as its potential. It’s cheaper for the contractor
to buy a bigger unit and cut corners on the installation.
There’s a myth out there that a unit that runs for a longer
period of time costs more than one that cycles. For example, a
four-ton unit will consume twice the energy that a two-ton unit
will if both run the same length of time. But when you factor
the cycling effect on efficiency the four-ton will consume up
to 20-percent more electricity. Electrical usage (expense) is in
direct proportion to system size and efficiency, so you want to
make sure that you are using the correct size system for your
home. In fact, researchers at Texas A&M have determined that
slightly undersized units are more efficient and better at provid-
By Brett Hobson
CEO Comfort Experts
ing comfort.
After the correct size has been determined, ask if new duct-
work will need to be installed. Make sure if they are using the
current duct system that it is clean and in good repair. You don’t
want to install a new system into leaky ductwork.
Ask about any new technology that is on the market. There
are great new tools like digital or remote-operated thermostats
that can greatly improve the efficiency of your system by learn-
ing when you are away from the house, or you can turn on
remotely. Anything that saves a few dollars is worth looking into.
Do some research and know what is out there.
Make sure the system you are installing is the most efficient
one possible. Ask about the unit’s SEER rating. The Seasonal
Energy Efficiency Ratio (SEER) measures air conditioning and
heat pump cooling efficiency, which is calculated by the cool-
ing output for a typical cooling season divided by the total
electric energy input during the same time frame. A higher SEER
rating means greater energy efficiency