This duct to the outside is your fresh air supply to the home.
It depends on how tight your house is, if it will cause any ill effects.
- Newer homes, because they are built tighter are required to bring into the home a prescribed amount of fresh air per the ASHRAE 62.2 Ventilation & Acceptable Indoor Air Quality in Low-Rise Residential Buildings standard set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers.
- Not knowing the age of your home, this pipe could have been the low cost solution at time of construction to satisfy this requirement, which is very typical of builder homes in the late 90s and 2000s.
- However, if you have an older home, a previous homeowner could have had an energy audit performed on the house and it was recommended to them to have the duct installed to improve the indoor air quality of the home due to a low blower door test number.
However based on my experience it is my recommendation to remove the insulation from the duct and install a mechanical damper with a timer on it so the duct only stays open a prescribed amount of time. I installed one by Aprilaire a couple of years ago and noticed a big difference in our indoor air quality because we did not have any ventilation before.
Although if you are still concerned about the cold air that is being drawn into the home, there are alternative ways to bring fresh air into the home. Read this great article from Greenbuildingadvisor.com that discusses the way to ventilate your home.
For more information:
Read "How can you add fresh-air ventilation to an old home with a forced-air system and only supply ductwork throughout?" a Q&A answered by Danny Kelly.