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How Much Energy Do Cat Doors Waste?

Posted by Matt Power, Editor-In-Chief

Jul 8, 2014 9:19:00 PM

The Bottom Line: Passive leaks around cat doors waste WAY more energy than slow moving cats.

NOT ALL CAT DOORS ARE CREATED EQUAL. Some are rather flimsy, with very little in the way of weatherproofing, others go to great lengths to seal out unwanted air infiltration (and racoon infiltration, in the case of the one shown in the photo!).

Electronic Cat Doors

Smart SensorsThis electronic cat door identifies the pet by way of an implanted RFID.

To get an idea how much energy  poorly made cat doors waste, we can refer to standards for household doors.

First, I'm going to throw a short explanation at you from Rocky Mountain Power, a utility company, about how to estimate the heat loss through an open door or window: Don't worry, there's no quiz!

"Air leakage is a function of the temperature difference between the inside and the outside, as well as the size of the door opening. The first thing to do is to estimate the amount of air in cubic feet per minute (CFM) that will be moving through the open d oor at various temperature differences."

Let's skip ahead past the mumbo jumbo. These building science experts offer this handy chart referencing energy loss through an 8x10-ft. opening under specific conditions:

"For an outside temperature from 25°F to 50°F, and assuming a gas rate of approximately $1.20/therm and an 80 percent efficient furnace, the results shown in the table below are reached."

Heat Loss Through 8X10 Foot Door Opening

Outside Temp

Total CFM

CFM/ft² door opening 

Heat Loss (Btu/hr)

Heat Loss Cost ($/hr)

20°F

5,580

70

300,000

$4.13/hr

25°F

5,250

65.6

255,000

$3.51/hr

30°F

4,930

62

213,000

$2.93/hr

40°F

4,220

53

136,700

$1.88/hr

50°F

3,400

43

73,400

$1.01/hr

Keep in mind that hot air does not always rise. It's not as dense as cold air, so it's looking for an easy way out of the house. And when it leaves, cold air comes rushing in to take its place.

Let's say you have a SLOW CAT, who saunters through the cat door 100 times a week, adding up to an hour of door open time. Even when the air outside is coldest, the energy cost for using the approx. 1-ft square door would only be 1/80th of the number shown on the top right of the table, or $.05 (5 cents per week!) Let's say the door leaks constantly, to the tune of about 3 inches of overall gap. That's an hourly impact of roughly a penny per hour, or $1.68 per week (24 hours a day x 7 days at $.01 per hour). That's $6.72 a month, or $40.32 over the course of a 6-month winter.

Maybe it's worth spending a few extra bucks on a cat door that doesn't leak, eh?

The video below from Freedom Pet Pass doors. They make a model that looks pretty impressive, with an emphasis on air sealing.

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