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In the summer, we use a window air conditioner in our bedroom to be able to sleep comfortably at night. It takes a while to cool, and I know it uses quite a bit of energy. Here are a few steps we take to reduce total energy usage:

  • Set the mode to "energy saver," which turns the fan off periodically once the temperature reaches the set point
  • Set the thermostat to 78F / 26C
  • Keep the bedroom door closed when the AC is running
  • Keep the bedroom blinds closed during the day so that the room doesn't heat up too much

What are some other steps I could take?

There is a gap of about 2cm under the bedroom door... should I seal this? Will it make much difference? I also didn't invest much time sealing around the AC where it goes through the window. There are no large gaps, but are there ways I could improve the air sealing?

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Here's a few things to try:

Increase the temperature setting on the Air con

Air conditioning units typically do two things: lower the ambient temperature, and remove humidity from the air. Depending on where you live the humidity can be a bigger factor in getting a good night's sleep than the temperature itself, as it exacerbates sweating and makes the air feel thicker.

If your aircon window unit is set to a higher temperature, it won't need to work as hard to maintain it, but it can still remove a lot of the humidity from the air and help you get a better night's sleep.

Clean the air filter

Look at your air conditioner's filter on a regular basis, especially throughout heavy use times. If the filter seems dirty after a month, clean it (or replace it if it's not a reusable one).

A dirty air filter is likely to slow air flow and make the unit work harder in order to keep you warm or cool — burning up energy and increasing the chances of maintenance issues down the line.

Have your air-con serviced

Air-cons need occasional maintenance especially if the unit is getting on in age. It's best to have this done professionally. The service person will generally check the refrigerant gas levels, test the thermostat and make sure all the internals are in good condition.

Compare the efficiency of your air-con with newer makes

Depending on the age of your unit, there may be more energy efficient options available on the market. Definitely double check the energy efficiency before making a purchase.

Home-level changes:

Depending on whether or not you own or rent these options may or may not apply, but consider the following:

  • Check for air leakage - Not just under doors, but gaps in window frames, cornices, around vents or downlights, gaps in floorboards (they shrink over the years). This site gives a good overview of the sorts of places to check and gives good guides for detecting and mitigating air leaks.
  • Insulate - Add Roof batting, Underfloor (or undercarpet) insulation and if possible, wall insulation. Insulation works double duty - helping to maintain warmth in winter and cold in summer.
  • Install Double-glazed windows - basically the same thing as insulation but for your windows, one of the primary ways heat (or cold) escapes a room
  • Door Seals - look at installing proper door seals for doors with gaps.
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To reduce the effect of the 2 cm gap under the door you could attach a door sweep.

Any gaps around the air conditioning unit in the window can be sealed with silicone sealant.

To reduce electricity consumption, ensure the air conditioner is the correct size/capacity for the room it is supposed to cool. An undersized unit will continuously operate and under humid conditions outside, the compressor will freeze over. This will cause the air conditioner to cease cooling, which would require the air conditioner to be switched off so the ice melts and the compressor dries out. An oversized unit simply costs more than is required.

If possible, providing shade to the outside walls and window would reduce the amount of solar heating the walls and windows receive. Trees, shrubs, an awing or shutters can assist with this.

Retrofitting insulation, at least to the ceiling would be helpful, but if the walls can be done, even better.

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Well, simple aluminum-frame storm-windows, that are made to any size, can be easily installed over existing windows. Insulation can possibly be added over the ceiling in the attic and under the floor in the basement.

Of course the house heats up during the daytime but a steel standing-seam roof-covering, with a special granulated paint, will reflect solar heat and make a cooler house in the summer. In fact a 430, 444, or 304 stainless-steel roof-covering will work just as well but never need any painting.

But consider that most any house could benefit from having a floor-level cold-air-return in the winter but also having a ceiling-level hot-air-return in the summer. Or a ceiling-level hot-air-vent could be made by knocking a 304 pipe through the wall.

Finally, a hardwood tree can shade the house in summer but let sunlight through in the winter. And window awnings can help keep the house from heating-up during the day. But a tree has water evaporating out of its leaves and that's natural shade versus artificial shade.

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