If you are planning to install an HVAC (heating, ventilation, and air conditioning), then you should know that the entire design of the system (sizing and placement of air ducts and registers, among others) is just as important as the type of the installed system. Here are some examples of poor placement of air registers during your heating and air conditioning installation:
Return and Supply Registers Near Each Other
In an efficient register design, fresh air delivered by the supply register is supposed to circulate around a room for sometime before getting pulled back by the return register (after it gets stale). This will not be the case if the return and supply registers are placed next to each other; for example, if one is placed above a door and the other is placed below the same door. In such a case, the supplied air will just take the shortest route to the return grille – a phenomenon known as short-circuiting. This means your HVAC will be working but you will not be enjoying the benefits of its operation (for example, you will still be breathing in stale air).
Return Registers Next to Combustion Appliances
Another common mistake as far as placement is concerned is to place the registers next to combustion appliances. There are two main reasons why this is bad; first, the return registers can pick up exhaust gases from the air around the combustion appliance. It becomes even more dangerous if the appliance is malfunctioning and emitting carbon monoxide, which is a poisonous gas. Secondly, the return register will be competing for air with the combustion appliance, which may reduce the efficiency of the appliance. Therefore, return registers should not be placed next to water heaters, stoves, and fireplaces, among other combustion appliances.
Return Registers in Wet and Moldy Places
Lastly, it is also bad practice to place return registers near wet and moldy places. For example, if you have an unfinished basement with damp walls and floors, or even suspected mold problems, you should not use it for a return register. The air around those places is likely to be stale, and the return register will just be sucking in polluted air. Don't forget that mold is a poison that has been linked to a variety of respiratory health conditions.
This is why it's important to consult an HVAC technician when remodeling your house. The remodeling may leave your registers in the wrong places even if they were properly installed in the first place.