If the home is too tight air will be pulled in from the outside. Try the Skuttle Self Adjusting Makeup Air Controller. Getting a house too tight saves energy; so too tight is just right in my book. All you need to do is control the source of air that your combustion appliances are pumping outside. Furnaces, hot-water tanks, bathroom vents, vented kitchen range hoods and clothes dryers depressurize a building. Window condensation article.
Atmospheric combustion appliances use air from inside the home but newer sealed combustion furnaces and hot-water tanks draw outside air for combustion, so these units do not depressurize a building.
The furnace, hot-water tank (atmospheric combustion) and dryer need air to operate efficiently. Bathroom and kitchen venting efficiency is also greatly reduced when working against negative air pressure. To solve this you need to provide makeup air to your home.
Insufficient makeup air in a home increases drafts around doors and windows creating a less comfortable residence. In extreme circumstances negative air in a home can draw air down the chimney bringing carbon monoxide with it.
If you need to let air into your house, you can do it in a controlled manner.
I recommend installing the Skuttle Self Adjusting Makeup Air Controller #216 to the cold air return of your furnace. It connects from the cold air return of the furnace to the outside of the home. It has a damper that opens to let in fresh air as the furnace and other appliances cause negative pressure in the house. It is important to locate the outside air inlet away from contaminated air like car exhaust or other fuel burning appliances.
This way cold outside air will mix with warm air in the cold air return of the furnace where it will be filtered, heated and humidified as it is introduced into your home.
Even if your home is not airtight you will enjoy increased comfort by controlling how and where makeup air enters your environment.