Kitchen Ventilation.
You need to have proper ventilation to the outside for your cook-tops and ranges, especially if you are cooking with gas. But don't run the fan longer than you need to or you'll waste money heating your home. And make sure the fan you use in your hood or downdraft vent is not too large since that would waste energy too.
FYI: Ventilation fans create a slight vacuum. To balance the air pressure, cold air is sucked in from the outside through cracks in the walls, around windows and doors, etc. Then your heater kicks in to heat up the cold air. This is why too big a fan leads to energy waste.
Worse, if the fan draws out so much air that cold air cannot come into the house fast enough to equalize the pressure, an oil or gas heating system may not vent properly. This situation may lead to a backdraft of combustible gases into the house. Can you say "Boom"?
The backdraft problem is a big concern with large downdraft ventilation fans used with some cook-tops and ranges. You should ask about make-up air ducts for these. Some manufacturers offer make-up duct options.
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