I have a new house with a metal roof and without a ridge vent. Please recommend a vent system without cutting holes in the metal roof.-Bjorn
That would depend on the style of roof you have. If your house has a gable roof, you can install a vent in each gable then mount an exhaust fan in the attic behind one of them that is controlled by a thermostat. If you have a hip roof, you would either have to replace the existing ridge with a vented one—making sure the roofing and sheathing at the peak are cut back so air from the attic can escape through it—or mount a power vent fan on the roof itself, which would require cutting a hole in the roofing.
If you decide on a roof mounted fan, position it high up on the back of your roof, but not so high that it is visible from the front. Solar powered models are available that don’t require wiring, though they are more expensive than hard wired ones. Be sure the soffit under the eaves is vented so outside air can enter the attic.