Kitchen exhaust fans

All kitchens should have exhaust fans, a lot of hood fans do not vent the bad air to the out side, but instead they push the air through a charcoal filter and than exhausted it back into the kitchen. When these hood fans are used over 50 hours of use the charcoal filters should be changed. If you don’t, are your doing is blowing the smoke and cooking smells into the rest of the house.

Using an exhaust fan below 300 Cubic feet per minute, most houses have areas that leak this much air into these houses. Newer homes leak about 150 cfm around windows and doors.
If an exhaust fan is turned on blowing out 300 cfm, your short 150 cfm and it will draw it from a bad source. One of the easiest places for the air to come into the house is by sucking the air out of the chimney either the fireplace or the furnace chimney.

We remodeled a house along with the kitchen; we installed a 1280 CFM exhaust fan. We told the homeowner that he need makeup air he refused Than came thanksgiving, the family was there the owner has a 5’ wide and 4 tall open wood fireplace the fire was going for about an hour when the wife turned on the kitchen fan. Instantly the fireplace chimney reversed bringing the smoke into the house the fire in the fireplace was still burning but the flames were blowing horizontally into the room. He wanted a quick fix so he had a 12” fresh air intake installed into the cold air return on his furnace. This did fix 1 problem the fireplace now works properly while the kitchen fan runs on full speed.

If the furnace is running it was not sided to handle super cold air coming into the heat exchanger. With this much cold air coming into the furnace, the furnace cannot heat the house because now it has to heat the incoming cold fresh air. The other problem is that the heat exchanger is being stressed with 400 ° on the burner side and -10° on the other side this shortens the life of the heat exchanger by years.
If the house is warm because of the fireplace the furnace won’t turn on. With the fresh air dumping in to the return air plenum, the super cold air is now coming out all the vents cooling down your floors making a draft along the floor to the fireplace and the kitchen stove.
The proper way is to bring fresh air into the house and run it through a furnace designed to temper the makeup air.