that depends a lot on the HVAC spec and how big is the single vent. If it can handle certain size of the HVAC unit.

Read other post will give you some idea of how big it should be.

What type of home and how many sq feet basement or crawl and location of air handler/furnace would be helpful. I like having room specific returns but if not done and sealed correctly it can lead to a lot of re-work. For comfort I would say each room other than the kitchen and bathrooms.

Laura,

What area do you live in? In Ohio it's common for each room to have returns. But in Fl. they usually get away with one in a central location. It does't work very well in a large house. Some rooms don't get cooled properly.
Scott

I don't have specifics on the system overall yet as we just finalized the plans and we are waiting on the construction drawings.

That said, our house will have 3300 sq ft on the main floor, and 1000 upstairs. It will have two furnaces and AC units, with the furnaces being placed in the attic.

We live in Northern California, and our house is built on a crawlspace.

I asked the question because I had thought from reading on here that new construction was commonly set up with multiple air returns, and when I brought it up with the archetict he didn't know what I was talking about.

Have you considered installing the furnaces on the first floor in a utility room? How high is the crawl space? It may be possible to install the first floor furnace and duct work in the crawl space. It is best the HVAC equipment is inside the insulated envelope.

We can't put the furnace on the first floor in a utility room as there isn't space, and the crawlspace isn't very high (I don't know the exact height).

There will be two AC units, and two furnaces, though I was told each furnace would only have one air return which I thought was odd given the size of the house.

Here is our floor plan:

Home will have one system or two?

IMO

Two systems.

Minimum 1 upstairs

Minimum 3 downstairs

Of course, I prefer individual room returns. That is a mark of quality you rarely see today in new construction.

And for central returns, doors have to remain cracked or at least cut at bottom to allow air movement.

IMO

Thanks! I asked for one in each bedroom and our designer had not heard of such a thing so I thought maybe I was the one who was confused!

I know it is regional and based on many factors, but any idea how much it would cost to add extra returns?

IMO, you get more air circulation by having return in the center of the house and vents at each room. It cost less and having less duct work in the attic so I can get around more up there.

Some people prefer to have the bedroom door close all the time. If that is the case return in each room is better.

Sizing the return and the vent correctly to meet the CFM requirement for each system matters. My house has 2 20x20 return air for a 3 tons system and 2 20x30 for the 4 tons system.

your mileage will vary.

In my area, southern Texas, all most all upper scale new houses have individual returns (in every room), I am in one, they are much better and much comfortable compare to the old houses (with one or 2 returns).

As many as you can afford up to one per outlet.

Individual returns have a cost and I believe it was about $1000 per floor if we wanted that but that included a central filter. The returns have an ongoing cost if the ducts are not in conditioned space.

Laura - are you insulating the attic rafters? Ductwork or units in the attic is less than ideal unless you are insulating the rafters. A lot of the time insulating the rafters is a big expense that wouldn't be needed if the ducts were just relocated.

In NC, it isn't common to have individual returns but it is done. I have both and to be honest, it isn't a particularly big deal. When I say I have both, the master has its own returns.

Hmm... Lots to think about. I think I'd be happy with just extras in the bedrooms (and at a minimum one extra in the master bedroom.

I don't know much about how they are putting the furnace in the attic, and how the attic is being insulated just yet... I just know that for new construction it is extremely common in our area for it to go there.

I'm probably over thinking this as I doubt with a well insulated house in our area that we will use the heater all that often!