In many homes, the fresh air intake is just an open duct flowing from an outside vent into a basement or other room where the furnace is located. Fresh air intakes may be found throughout your house, particularly in newer homes according to contemporary construction requirements, which require dwellings to be considerably tighter than older buildings. The National Safety Council recommends installing fresh air intake vents in all living rooms and bedrooms above grade level.
These vents help to ensure that air within your home is always moving. If a door or window is closed but unglazed, then warm moist air will slowly find its way inside. This can cause mold to grow if there is moisture present such as from damp walls or flooding. Closing off the opening with a screen will help prevent this but it cannot be completely prevented. It is important to remember that even with a screen installed, someone could remove it and go inside without you knowing. This would allow in-coming air but not out-going air which could lead to problems for people with allergies or asthma.
People often ask me why my house doesn't have an air conditioner. Well, it used to be one! When I bought this house in 1990, it came with a very small unit that only cooled about 250 square feet. I had it repaired so that it could cool a little more than that but not enough for today's standards. I also had the filter replaced because it was pretty dirty.
Furnaces, regardless of the kind installed, require fresh air intake since they are normally intended to push air out of the residence while operating. With the fresh air intake installed, you can ensure that the furnace's combustion does not degrade the air quality in your house. You should also install an exhaust fan if one is not already available with the furnace.
The type of furnace you have will determine how the fresh air intake and exhaust fan are connected to it. For example, if you have a forced-air heating system, the intake and exhaust fans will be integrated into the ductwork and will need to be large enough to provide adequate ventilation without causing resistance problems. If you have a heat pump, the intake and exhaust fans will attach directly to their corresponding units and will not have any ductwork associated with them. They will usually be about the size needed to move sufficient amounts of air through the heater or cooler when it is operating at its maximum capacity.
Since furnaces are used to heat homes, they should only work hard enough to do so. If they are working too hard, they will be inefficient and waste energy. This could lead to higher electricity bills and less comfortable temperatures inside the home. A furnace that runs all the time uses more energy than one that is turned off at night. However, if it is not running for some reason, it could cause problems with pests such as insects coming into the residence through open doors or windows.
It is determined by the home and the system. You haven't supplied much information in any case. Because older dwellings are frequently drafty enough to supply ample combustion air, a specialized intake is not necessary. Modern dwellings are frequently considerably more tightly sealed, necessitating the use of air intakes. However, even these intakes do not always need to be external, depending on how they are designed. For example, some internal units run off the main air handler while others don't.
The answer depends on how the house was built and what kind of heating equipment is used. But generally, yes, all houses have them. They can be located anywhere from under the eaves of a roof to inside the wall with an exterior unit.
They draw outside air through the roof or floor into the house where it is filtered by any insulation or weather stripping that may be present and then distributed around the building via ducts. The amount of outdoor air that enters a house through an intake equals the number of people living there plus one if a pet is kept outside. If you add up the number of people and pets who will be breathing in fresh air each day, you'll know how much needs to be brought in.
Intakes can be either internal or external. External ones are usually placed near the top of the wall, below the soffit, because this is the best place to get clear air while keeping out snow, rain, and heat.