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Get the Most From Your Central Air Conditioning
(and save big money on your power bill)

This was written for Canadians with central air conditioning. It also could be applied to the USA and other countries.

In my 40 years of owning A/C homes in Ontario and Quebec I've learned a lot. Many of these tips will probably be found on other web sites but not all of them!

Do you have an efficient home A/C system?
When turned on does your A/C system go on and off all day and all night? This is an indication that it is working correctly. Or does your (outside) compressor stay on all day and most of the night? (Not good). On very hot days does the temperature inside your house rise even with the air running? (Really bad).

Set your thermostat for summer and forget it
Pick a temperature that you want your house to be in the summer.  You might have to experiment to find the right temperature that is comfortable for you and your family. I use 23° (73.5 F). Do not set too low it is not necessary. Do not set too high our local hydro company recommends 26° (78 F) at this temperature you will probably sleep above your blankets on hot nights what's the point of owning air?

Keep the furnace fan on permanantly
Turn on the "fan" at your thermostat and leave on for the summer. It will cool your upstairs with basement air - even when your A/C is not running.

Learn to turn your A/C on and off
In Canada we often have mild summer days and/or nights. Check the expected temperatures for the day on the TV in the morning. If it will be mild turn your A/C off (at the thermostat) and open your windows. Same for nighttime. Do NOT change the thermostat temperature! Learn to do this daily.

Close all the windows
When running air conditioning keep all the house windows closed tight. Ensure your family complies!

Use your curtains & blinds
Radiant (sun) energy through your windows will warm the rooms more than the hot air from outside! Keep your blinds, curtains AND windows closed.

Keep your lights off during the day
Lights generate heat and use power!

Stop A/C empty rooms
Have bedrooms that are not used? Close the window, blinds & curtains, close the vent, shut the cupboard door and shut the bedroom door. Who cares if the room gets warm? Same for all bathrooms in your house. Learn to close the bathroom door after each use.

Cupboard doors
Always keep cupboard doors closed in every room Did you really want to A/C all those old coats and children's toys?

Experiment with your vents
Find the right balance. All vents open on 2nd floor (except as above), most open on 1st floor and all vents closed in the basement. 

Maintain the airflow
Except for the rooms mentioned above all your vents should be open fully. You want good airflow through your furnace A/C system. Is your furnace air filter dirty? Start the summer with a new filter and check monthly. A dirty filter will reduce the airflow significantly. If the airflow is reduced too much, the A/C system will freeze into a block of ice and stop working! 

Too cold in the basement?
This is a common problem in most houses. This is caused because of an obvious combination of items. The A/C system runs through the basement furnace and is freezing cold, heat rises, A/C vents in the basement are not needed in the summer and there is often a poor "return" of air from the basement to the furnace. Even if you do not use your basement your objective is to send that nice cold air from the basement to the upper floors where it is needed. Always keep your basement door shut. Close every basement vent. I actually tape over the basement vents so there are no leaks. Check your basement air "return" to the furnace. Ensure it is open fully. Check the humidifier on the furnace. Ensure it is shut off. Is the humidifier sealed? I place a special cut piece of cardboard in my humidifier so all airflow is completely cut off. When the A/C is running check around the furnace for cold air leaks you'll be surprised at how many there are! Tape over any obvious leaks. 

Basement still too cold?
Here are a few more items that can be done to send that nice cold air upstairs. Remove the metal plate over the furnace filter. This will allow even more basement air to go upstairs. As a last resort, remove your furnace filter it will really improve the airflow!

My temperatures with the improvements I mention above - main floor 23°, upper floor 24°, basement 22°.

Living through a heatwave
Turn the air on and leave on until the heat wave is finished. Do not be tempted to shut off at night. 

Buying a new (or your first) A/C system
(1 Ton is about 12,000 BTU) 
Canadian contractor recommended sizes are 1.5 Ton for small homes, 2 Ton for 2000 square feet. 2.5 Ton for 2500, 3 Ton for 3000, etc. This is the absolute minimum and the recommended size will often not keep the temperature you request when the outside temperature exceeds 30°. I recommend that you purchase 2 Ton for small homes, 2.5 Ton for 2000 square feet. 3 Ton for 2500, 3.5 Ton for 3000, etc.

Buyer beware
When purchasing an A/C system the contractor will often send a salesperson to your home. See what he recommends before you volunteer your knowledge. Be careful if he recommends a system that is too small for your home. The price difference for a larger system should be very little (<$500). If he continues to insist on a (too) small system (for any reason) it is often because the contractor has already purchased several of the small systems and wants to unload them. He does not share your interest in giving you the correct system!

Still having problems?
Done everything above? But temperatures still climbing in your house on hot days? It could be you have an older home with thin wall insulation. Or you need more insulation in your attic. Or an attic fan to get rid of the heat up there. More shade trees on your property will really reduce your power costs and improve your A/C efficiency. But really you probably need a new (or larger) air conditioning system for your house.

Canadian Systems vs USA systems
As soon as you cross the border American systems are 50% larger. In the Southern USA systems are twice as big as Canadian systems.

Comments, corrections and additions
Are all welcomed. Please E-Mail me at


Most recent page review : 2009 08 20