My parent’s 2-story w/basement house (furnace in the basement) (built in 1942) has a supply and a return duct in every room, which makes the ducting massively complicated. My split-level house in Arizona (built in 1970) (a bigger house than my parent’s) has supply ducts in every room, but the return is just a big grate at the air handler. Our cottage in Colorado (built in 1959) is similar - supplies to each room, single return at the air handler.
Are any houses still built with dedicated return runs? When did the switch-over happen, and who decided that it was OK?
I’m not an HVAC expert, but my understanding of it is that it’s mostly a cost savings thing. Instead of having ducts run all over the house, you have supply vents around the outside of the house, then the air has to flow back through all of the rooms to the center of the house, where there is only one or maybe two return vents. Often the house will rely on a stairwell to provide the return path for the air, further reducing the need for return ducts.
It’s also supposed to be more efficient. When you have a whole bunch of ducts, you have to very carefully adjust each vent so that the air circulates evenly through the house. If you do it right, it works pretty well. Most people just leave all of the vents wide open though, so you end up with poor airflow through the entire house due to the differing lengths of each run of ducts. With the newer system, the air circulates through more of the house, making the temperature throughout the entire home more uniform.
In my experience, 1940-ish and earlier homes have either steam radiators or they have both supply and return vents in every room. 1960-ish homes often have baseboard water heat (the most comfortable kind of heat, IMHO), but if they have forced air, they have fewer ducts overall and significantly fewer return ducts. 1980-ish and later homes often have crappy heat pumps (great for efficiency, crappy for comfort) and since the heat exchanger is typically outside and not in the basement, the vent and duct layout is significantly different.
FWIW, Google’s bullshit generator says that the shift occurred between 1960 and 1980, which matches up with my experience.
Poking around online, it seems that some new homes are made with returns in every room, thogh they are much less common than they used to be.
I don’t know, but I bet the answer is in your question: Having a full second set of ductwork throughout the house for the return is way more complicated - and expensive - than a single set with a common, centrally located, intake.
Our house was built in the mid-1950s. We have two returns, one in the living room, one in the master bedroom. That essentially divides the airflow into two zones offset at a 45 degree angle.
Another change I’ve noticed is that one-story houses built before 1950 typically have supply ducts in the floor. Since heat from a forced-air furnace rises, that was efficient. When houses started being built with air condtioning, the vents were placed near the ceiling, because cold air would sink. Probably less efficient in winter, though.
As already mentioned it is a cost saver to have a single return. But a system with supply and return in each room allows you to have the doors shut and still heat evenly. My 1925 house had multiple returns but they just opened into the crawl space. I installed a complete closed system myself.
My 1940 home has two floor returns on the main floor (furnace is in basement).
My 1905 home has one large return on the main floor. Furnace is in walk-in crawlspace. House has two above grade finished floors (the attic is also finished but I don’t count it because that finishing came much later.
Our 1940 home could pull return air at the furnace but that would be pulling much cooler air. Our 1905 could not since it is outside the conditioned envelope. For both houses, it makes sense to pull return air where they do.
The 1912 house I grew up in had a single return on the floor in the living room. The furnace was in the basement. So I don’t think that a return in every room was universal in old houses.