[retiredguy123]

Originally Posted by C. C. Rider

I disagree. Without insulation in your garage ceiling, during warm weather months you'll have attic temperatures of about 135* to 140* depending on the amount of ventilation in the attic.

Some of this heat will radiate down into the garage through the uninsulated ceiling which will make the garage even hotter.

Insulation in the garage ceiling will make the garage cooler whether you have any AC in the garage or not.

Also, I would advise keeping the attic access door in the garage ceiling closed at all times that it's not being used. Leaving it open will allow some of that super-hot air in the attic to come down into the garage. I know because I've tested it both ways. If the hot air did NOT come down, there would be no reason for a ceiling at all. You could just attach your garage lights and door openers to the ceiling joists.

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The heat from the attic will transfer to the garage anyway. The insulation will only slow it down a little. That is why builders never insulate between unconditioned spaces.

[C. C. Rider]

Originally Posted by retiredguy123

The heat from the attic will transfer to the garage anyway. The insulation will only slow it down a little. That is why builders never insulate between unconditioned spaces.

You mean that SOME builders don't insulate the garage ceiling. Insulation slows down the heat transfer CONSIDERABLY. If you don't believe it, then wait until a really hot afternoon and take a temperature gun and compare the ceiling temperature in your uninsulated garage to the ceiling temperature in your living room.

If you're going to insulate the walls where there might be a temperature difference of 20* on a hot afternoon, doesn't it make sense to insulate the garage ceiling where there might be a temperature difference of 40* or better?

My garage ceiling is insulated.

[Topspinmo]

Originally Posted by retiredguy123

Without a heating and/or cooling source, like a mini-spilt system, the insulation will be almost worthless. Ventilation may move some air around, but it really won't have much effect on the garage temperature.

But it will on his sweatie body, moving air cools hot body. My garage has never got above 89 degrees in 95 degree hot summers, so something making it cooler?

[retiredguy123]

Originally Posted by Topspinmo

But it will on his sweatie body, moving air cools hot body. My garage has never got above 89 degrees in 95 degree hot summers, so something making it cooler?

For one thing, you don't have the radiant heat transfer from the sun inside the garage. Outside the garage, the sun heats up surfaces and the surfaces increase the temperature of the air.

[vintageogauge]

I had them installed with dampers, 2 at the bottom of each door painted to match the door along with a thermostat controlled roof exhaust fan and it made a noticeable difference. Some say it brings in hot air which I'm sure it does but heat rises and it is then sent out through the exhaust fan and once the sun move around it pulls in cooler air for the evening and throughout the night. When you go into the attic to get something you can really feel the cooler temperature up there. Well worth the effort and cost which was minimal.

[Topspinmo]

Originally Posted by retiredguy123

For one thing, you don't have the radiant heat transfer from the sun inside the garage. Outside the garage, the sun heats up surfaces and the surfaces increase the temperature of the air.

Yes, IMO but air temperature still 95 degrees. So why isn’t the garage 95? Insulation if nothing else just from building and transfer from inside house temperature?

[Topspinmo]

Originally Posted by vintageogauge

I had them installed with dampers, 2 at the bottom of each door painted to match the door along with a thermostat controlled roof exhaust fan and it made a noticeable difference. Some say it brings in hot air which I'm sure it does but heat rises and it is then sent out through the exhaust fan and once the sun move around it pulls in cooler air for the evening and throughout the night. When you go into the attic to get something you can really feel the cooler temperature up there. Well worth the effort and cost which was minimal.

Isn’t moving air cooler that stagnant air?

[retiredguy123]

Originally Posted by Topspinmo

Yes, IMO but air temperature still 95 degrees. So why isn’t the garage 95? Insulation if nothing else just from building and transfer from inside house temperature?

In addition to the radiant heat transfer from the sun, you may also be getting some cooling effect from the air conditioning in the house. But, I think most of the temperature difference is due to the sun heating up the driveway and other outside surfaces. The driveway gets hot and transfers heat to the air.

[vintageogauge]

Originally Posted by Topspinmo

Isn’t moving air cooler that stagnant air?

Is it?