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.
MY 1909 built 2-story house has a supply vent and return in each room on the first floor, but the upstairs has only supply vents in each room – no returns. That’s fine in winter, extra heated air rises up the open staircase to the second floor. But in summer, the central air doesn’t cool the upstairs nearly as well as the downstairs – heat from the attic bleeds down into the upstairs rooms, and there are no return vents to pull it back thru the AC.
To cool the upstairs to the desired temp, then the downstairs is too cold (and the AC is overworked). Adding an upstairs return vent, even a single central one, would be helpful – but that’s hard to do in an old house.
Much less efficient in the winter. My home was built in the mid 50s and had the supply vents on the wall close to the ceiling, producing a definite comfort zone. While standing, you were comfortable from about mid-chest up but once sitting, it was best to wrap up in a blanket.
Supply vents are now on the floor, and I’ve noticed no adverse effects during the cooling months.
All of these discussions also have a significant local component.
In the USA we have regions where every house when built had/has AC but few to none have heat, where every house has heat but few to none have AC, and areas where full HVAC is the norm. Some of which are combined systems and others separate.
The typical, much less ideal, ducting for each kind is different.
So it’s worth mentioning generally where our various anecdotes are coming from.
Is it a forced air system or an old gravity furnace system? The house I grew up in had an older gravity furnace that had returns from each room , in addition to the hot wheels / Lego pit of death in the first floor hallway…
My current (Canadian) house - built about 20 years ago - has returns in most larger rooms. The return duct parallels the furnace duct down the middle of the house (alongside the center beam). It’s less complex, as for example there are several hot air ducts in the open living room-kitchen-dining area, but only two returns. Same with the master bedroom. Return ducts also are on the inside walls of the rooms, while the heat ducts are along the outside walls, usually under the window(s). So the return ducting is less complex, fewer vents, shorter runs, but not trivial. Most ducts are near the floor, so hot air (theoretically) goes up the outside wall, cools, and is returned from the inside wall of the room, to help prevent dead spots. (And as usual, the same venting works for heat and AC). Obviously the furnace includes a fan which pushes the air out, thus creating inbound suction… Every so often we notice and clean the air intakes where dust accumulates…
Rather than return ducts, the bathrooms have a vent to outdoors. To make it easier to retain heat, all 3 of those exhaust vents go through a central heat exchanger.
I have done some minor fiddling with the vent openings to help distribute the air better. I assume to some extent this is state of the art new house construction in Canada.
My parents’ house, built in 1962, is a slab ranch with one return in the middle of the house. My house, built in 1969 in the same neighborhood, is a raised ranch with a basement and I’ve got returns in every room. Also, all of the ducts go into the wall cavities, and a couple runs in the basement consist of a piece of sheet metal covering two floor joists.
I’m guessing that for a house with a basement and no second floor, the ducting was easy peasy and they could do it the way they did with no extra cost. For my parents’ slab, it would have been a heck of a lot more planning and work to add any extra returns - and for how small the house is, probably negligible airflow improvement.
Works as in it functions yes, but not as well. In a heat-only system low supplies and low returns are great, because as you said the heat rises up and mixes while the cool air falls and gets sucked in by the return. Similarly for a cooling-only system, high supplies and high returns perform the best. However for a system that both heats and cools, you want the supplies and returns not only at opposite ends of the room (best practice in any system) but also opposite heights to prevent stratification.
If you retrofit air conditioning to an older heat-only system with low supplies and low returns, the cold air sits near the floor on a direct path between the supplies and returns, never scouring out the bubble of warm air above waist height. It’s even worse if it was a gravity hot air system that has oversized supply ducts and just one big return on the first floor. The denser cold air is harder for the blower to push, and it doesn’t want to rise up to the second floor which was probably under-supplied in the first place. Bonus if the supplies are on the wall blowing out into the room rather than in the floor blowing up. So the dribble of cold air you get on the second floor immediately heads to the stairs to fall back down to the first floor where it’s already too cold. You can mitigate that with very deliberate adjustments to dampers and registers but it’s difficult to dial in.
Conversely, forced air heating where the supplies and returns are both in the ceiling is subpar because the heat just stays up there and gets sucked back into the return. This is especially true in most commercial drop ceiling installations where the supply diffusers are specifically meant to spread out the air to eliminate cold drafts in the summer, but they’re terrible at pushing heat down in the winter.
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. Often for practical purposes in homes, the former is what you’d do on the first floor with a furnace in the basement, and the latter is what you’d do on the second floor with a furnace in the attic or a closet. If you’re stuck with low/low or high/high then unidirectional ceiling and floor supply registers are better so they can push the air up (or down) and better mix out those warm (or cold) bubbles. Ceiling fans help too.
I worked as a sheet metal apprentice at my father’s HVAC business 40ish years ago. I don’t think things have changed much since then.
If a HVAC system is installed while a stick-built house is being built, a dedicated return is still used, but it doesn’t use metal ductwork. Instead, one or more of the gaps in-between joists in the area between floors in a stick-built house are used. They just block off the bottom and block or open ends as needed to create a “duct” for the return air to pass through. They may leak (actually suck in) some air from other spaces, but it doesn’t matter much because it’s negative pressure. In the pic below, the round metal duct is the supply and they could easily use the empty space between the two joists to the right of it as the return air duct by closing off the bottom and punching a hole through to the other side.
When HVAC is added to an existing home, unless the walls & ceilings are gutted, they don’t usually do that. They just add a grate at the air handler then insure return air can flow between major areas by adding a few strategic vents in walls.
Far too late to edit - the house is in New England, has gas heat but did not have central AC when it was built. Built by a builder on spec. Given the many other cost cutting measures the builder made (no exhaust fan in either bathroom, single GFCI in basement covering all code-required GFCI outlets, no dedicated breakers for gas stove or microwave), I’m surprised they went to the cost/effort of individual returns.
The problem is making something that works for both hot and cold. I suppose in Canada, heating is the priority and so the ducts and returns tend to be on the ground. Since the supply vents are pointing upward, even cold air when pushed gets some assist to go up. I’ve never noticed an excessive heat differential on height.
This is sort of how my house is built. The returns are close to the center beam, which is flush with the bottom of basement joists, so where a return duct is, there’s metal between the joists to close off the return and direct it to the return main duct. It saves a bit of ductwork.