Optimizing your AC: How to reduce the costs of keeping your house cool.


Lower The Costs of Keeping Your House Cool In The Hot Ontario Summer

This is a favourite topic amongst Air Conditioning and HVAC professionals – which does not mean that there is agreement. This is not a straight forward problem – so much of what is ‘best for you’ is a function of your personal preferences on living conditions (do you like it hot or cold, etc.), your budget, and the layout of your house. Remember that any solution for cost savings should take into account time of use pricing for residences in Ontario.

Let me start with the last topic – the layout of your house. Depending on when your house was built, you may have trouble getting the upstairs of your house cool in the summer. The older the house, the more primitive the ducting system moving hot and cold air through your house. A common response is to increase the size of the AC by upgrading. This may not help at all. When the stat calls for cooling the Air Conditioner helps to push cold air into your duct system. While this may move air to the upstairs, if there is not sufficient return air (ducts moving warm air back down to the basement) there will be no place for this cold air to go. Remember, the AC only reacts to what the thermostat tells it to do, and the thermostat can only see the temperature right where it is located. Unfortunately, it doesn’t see how warm it is on the second floor.

So, how can you cost effectively get cool air into the rooms upstairs in your house? The first step is to pay attention to the outdoor temperature over the course of the day. It may be warm outside at the end of the work day, and therefore you need cooling, however once the sun goes down the temperature can drop significantly. Use this drop in temperature to help you cool the upstairs. Open the windows (on opposite sides of the room so you get some circulation) and if necessary use a small fan to help move it through! When the temp starts to rise again in the morning and you’re going to be out of the house all day, try to minimize the ‘heating effect’ that the windows will have. Close them and draw the drapes / blinds – it’s not perfect but it sure helps the Air Conditioner.

If you find that the main floor of your house is comfortable but your upstairs is not, try helping some of that cold air up or warm air down. Put a large fan at one end of the stairs or another – if you chose to put it on the main floor, have the fan blow the cold air up. What is absolutely better is to put the fan at the top of the stairs and blow the hot air down! Think about it, what you’re actually doing is augmenting the effectiveness of the ducting system – helping to pull the warm air out of the rooms and push it downstairs so that the cold air can actually affect the temperature of the room.

The next steps are really dependent on your budget. Most of us don’t have too much money and are looking for ways to save a dollar or two. Here my suggestion is relatively simple. Have the Air Conditioner work hardest when the electricity is cheapest. In the summer that will mean definitely (on week days) from 7pm to 7 am, if necessary between 7 am – 11 am and 5 pm to 7 pm, and as little as possible between 11 am – 5 pm. On weekends you can run it as hard as you like anytime – the cost will not vary. If you want to get into more of the details have a look at our blog post on programmable thermostats from a couple of years ago. The exact costs will be different but the approach still applies.

The most obvious way to minimize the costs of running your Air conditioner in the summer is to buy a super efficient (hi SEER > 18) 2 stage Air Conditioner. The bigger coil size makes the compressor’s work so much easier so that you don’t have to use all of that electricity keeping your house comfortable. The Ontario Power Authority usually has incentives to lessen the financial burden and as electricity rates increase so do your savings!

So, to summarize:

  • Get preventive maintenance done so that your AC operates at peak efficiency.
  • When it cools off at night, open the windows and use a fan.
  • If your house is old, put a fan at the top of the stairs at night and blow the warm air downstairs.
  • Maximize your AC use when the electricity is cheapest. (Weekends, 7 pm to 7 am weekdays)
  • Buy the most efficient air conditioner you can afford.

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