Dockside Chat - high velocity a/c for home

I have a 1940 two-story stone colonial and I am looking to add central air.

I got a quote for a single conventional a/c system, with the air handler in the attic and ducts running to the first floor through closets, but the neighbor has that same set up and his first floor doesn't get cool enough because there are not really enough closets to run ducts down.

Next option would be high velocity. Anyone have experience with those? I understand they are not quite as efficient as newer convenitonal a/c, but otherwsie don't see much of a downside.

Only other option would be two systems, one for the first floor with the air handle rin the basement and one in the attic for the second floor, but that is substantially more expensive.

The two unit system is by far your best system.

It's strange that the 1st floor wouldn't be cool enough with a single unit in the attic. It's got to be more than "not enough closets for ducts".

A single unit with one zone will always have one floor too cold or too hot. There's no way to design a single zone two story system that would be balanced due to different loads.

The "high velocity" units work well IF installed properly. The typical problem related to these systems is excessive noise and installers that aren't properly trained.

Look at ductless systems

I'm piping my house with SpacePak right now... the noise is a concern, but my house is 1927. I'm re-siding the house, so it's easy to run the lines in the exposed walls rather than carving up rooms for larger ductwork. I'll deal with the sound, it's no worse than the window units I have now.

You can balance the system, or you can use zones.

I would Seriously consider the ductless mini split system or go with the 2 systems. Installing 1 system in the attic and zoning is an option too.
Do you know if the walls in your 1940 house are insulated? I've seen many that aren't.

noise can be kept to a minimum when runs shorter than 13 feet are piped with sound attenuator, unico and spacepak are great systems when installed properly.

one system is still going to give you a large temperature gap between the 2 floors. There are very few systems I have seen work 2 floors with close temperature gradient. Even if they try to load the second floor.

http://www.fujitsugeneral.com/cassette.htm

Google cassette AC systems

I'm piping my house with SpacePak right now... the noise is a concern, but my house is 1927. I'm re-siding the house, so it's easy to run the lines in the exposed walls rather than carving up rooms for larger ductwork. I'll deal with the sound, it's no worse than the window units I have now.

You can balance the system, or you can use zones.

The reason you can't "balance the system" is the loads are too disproportionate and in flux. On a sunny day, the 2nd floor might need 3 tons of cooling and on a cloudy humid day, the 3nd floor might need 1 1/2 tons. During both scenarios, the first floor might need 2 tons.

Even a single floor house is hard to balance as the load changes with the position of the sun.

It's all resolvable, it's a matter of $$$. A single zone system is going to be the cheapest. If you can live with the short comings, great. I don't know what a 2 zone properly installed high velocity system cost. Years ago, a conventional 2 unit system wasn't much more than the 2 zone HV.

The major installation problem for a HV system is in it's turns (elbows). A 90 degree turn take a lot of space and installers usually don't have the room to do it properly.

I had two buildings on the campus where I worked where the "enginers" designed a single unit to do two floors. Neither worked right and since one of them was where the ITs worked they were a constant pain in the asp complaining that they were to cold or to hot.
Go with dual units and forget the HV system.