With summers getting hotter and stickier, you may find your AC running non-stop so you can keep your cool. But the constant operation is raising your utility bill and your blood pressure.

So now is a good time to address the 20-degree rule, an axiom of HVAC techs everywhere.

It means you should not set your thermostat at a temperature more than 20 degrees cooler than the air outside.

That’s because most AC systems can’t handle a difference of more than 20 degrees between the inside air and the outside air. They will just labor endlessly, losing efficiency and life span while struggling – and often failing – to reach your desired indoor temperature.

This is not a major problem in New York summers except when temps pass 90 degrees and keep rising. The result: Your home or business may get uncomfortably warm even as the system runs and runs and runs.

You can keep the thermostat in the high 70s and take other measures – ceiling fans to move the air, dark curtains to block out the sun – and pray for rain that will cool the air. Also, hold on until September, when New York City generally gets only one day of 90-degree temps.

Premier HVAC techs handle all sorts of HVAC challenges in Queens, Manhattan, Long Island and Brooklyn, where the locally owned company is based.