For most people, during summer their air-conditioning unit is their best friend. (I’m not a big fan myself, but whenever they come over, my kids complain that it’s too hot .)

If the A/C shuts down when it’s really hot or during a heat wave, it can be torture. And one question that comes up a lot is what happens to a house that’s too hot?

The good news is that the majority of construction products we use in Canada are made for Canadian weather, which we know can go from one extreme to the other — we get very cold winters and extremely hot summers. So most products can stand up to the heat, especially exterior products and materials.

What we do get is expansion — remember, most materials expand in the summer and contract in the winter — and sometimes that expansion creates too much pressure and causes damage. For example, too much pressure can build up around windows, which could damage the windows themselves or break the insulation seal in between double- or triple-paned windows.

Obviously, a higher quality window will be able to handle this extra pressure better than a lower-quality product. But if it does happen, the window’s thermal barrier is compromised, which means the window might need to be replaced.

What about your roof? Can too much heat damage it?

The heat and sunlight hitting the roof might not — roofing products are made to handle that — but the real trouble will occur if there isn’t enough ventilation and insulation in the attic. That will really do a number on the roof, by causing, for example, asphalt shingles to curl and wear out prematurely, and mould and/or rot in the roof structure. As most roofing materials are dark (especially asphalt shingles) they’ll absorb more heat. If there isn’t enough insulation in the attic, all that heat will eventually make its way inside the house, warming it up throughout the day so that by nightfall it will be hotter inside the house than outside.

If your home is too warm, not only is it uncomfortable for the people inside, in some cases it can be a major health risk, such as for the elderly or small children.

Having too little insulation in the attic and exterior walls, too much moisture and not enough ventilation and airflow throughout your home (including the attic) can definitely cause problems, such as mould, poor indoor air quality, and in some cases even rot, inside the house. A proper HVAC system, which includes air conditioning, can help keep the home comfortable and safe, and protect against such problems.

But the key is to make sure you have a unit that’s properly sized for your home, which a licensed HVAC professional can determine, based on the square footage of your house. The more square footage a home has, the more powerful the unit needs to be.

But don’t go overboard. I’ve heard of people installing a heavy-duty A/C unit for their home — much more powerful than it needs to be — because they think it will cool down their house faster. It does, but it will cost you, sometimes even tripling your energy bill. When an A/C unit kicks in, it needs a lot of energy to start up, but once it gets going, it only needs a fraction of that energy to keep it running. An A/C unit that’s sized too big for a home will be turning on and off more frequently, which will make your energy bill skyrocket.

No one likes a hot house and no one likes high energy bills. Top up your insulation if you need to, keep the soffits clean and clear in the attic, make sure you have enough airflow and ventilation throughout your home, and always bring in the pros when you need to, especially when it comes to your HVAC and air conditioning.

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Source: Mike Holmes, Special to National Post | August 5, 2015 2:36 PM ET