When (and why) did home HVAC change the way return air is handled?

[Marvin_the_Martian]

@jjakucyk

So if you have a system that both heats and cools, you want either low supplies with high returns, or high supplies with low returns to maximize air mixing.

I’ve had at least two houses (both built since 2000) which had returns in each room with a door as well as central returns for the main open area. Each return had two intakes, one high on the wall and one low. The intakes had dampers so that in heating season you would close the upper return on open the lower, vice versa in cooling season. Only one supply vent type - in the floor or in the ceiling depending on the location of the air handler. I think this type of adjustable return height is pretty common in areas where heating and cooling seasons are similar.

My current primary residence in Arizona originally had large centralized returns for each air handler (two systems on opposite sides of the house). Rooms that could be isolated by doors had what they called “jump ducts” - a short length of ducting that ran from the ceiling on one side of the door to the ceiling on the other side. The two systems also had multiple zones with dampers in the ductwork controlled by local thermostats - the system could heat or cool whatever combination of rooms needed it. When we replaced the system we had them change the jump ducts to proper returns.

[jjakucyk]

@Marvin_the_Martian

Each return had two intakes, one high on the wall and one low. The intakes had dampers so that in heating season you would close the upper return on open the lower, vice versa in cooling season.

I’ve seen that a few times but I don’t know how common it is. That’s a good way to do it, but a bit more expensive since you need additional dampers and multiple grilles.

@Marvin_the_Martian

Rooms that could be isolated by doors had what they called “jump ducts” - a short length of ducting that ran from the ceiling on one side of the door to the ceiling on the other side.

Jumpers are a decent compromise if you don’t want to undercut the doors to allow air out. They also have a benefit in a second floor cooling application by creating a high return rather than what is effectively a low return with an undercut door. You just need to be careful about sound transmission.

[a6ka97]

My house (2 full stories + basement) was stick built in 2010. The HVAC contractor suggested having 1 large cold air return in the hallway next to the stairs on the main floor with the open stairway as the cold air return from the upper level to save some money. He also pointed out that in order to get good airflow when the HVAC was running we would need to leave the bedroom doors open for airflow. We decided this wasn’t the place to save money and had cold air returns placed in each bedroom.