Square footage cutoff for dual zone HVAC? (floors, grill, AC)

[dmann]

I am looking at building a 2200sqft house with a national builder in Apex. I was kind of surprised to see that it was single zone hvac with no option for dual zone.

My frame of reference is my current home which is 1700sqft with a cathedral ceiling and loft area over the living room, also single zone. After a few years we finally got a handle on the seasonal opening and closing of vents to get even heating/cooling throughout the house.

Without going into a full "Manual J" hvac sizing analysis on the new home, I was wondering if anyone had any comments on dealing with single zone in a house this size.

Square footage is about 1000sqft downstairs, 1200 upstairs with bonus over garage. The transition from first floor to second floor is a standard straight 15 step staircase.

[guest12]

I have a total of ~1700 square feet, 1.5 story, vaulted ceiling downstairs - it was originally built with one unit and a single zone, and it was miserable. When I had dual-zones installed, I was told that the house size was approximately the size at which two units should be considered (seems a little small to me for that, but...I'm not an HVAC specialist!).
2200 sq feet does seem like a rather large size for just one zone - but that's just my opinion! Good luck!!

[MikeJaquish]

Is the builder installing dampers in the ductwork to create zoning?

[frankpc]

Just my humble opinion but you absolutely need at least damper control to balance the temperature upstairs vs down. I would go with two zone/two compressors and adjustable thermostats on each floor myself.
I would also have a discussion with your builder about how they insulate the bonus room over the garage. Many folks have difficulties with temperature control in this space. Placing R-30 in the garage ceiling under the bonus room floor instead of R-19 and ensuring that the cavity remains well insulated with a thermal break will have very little incremental cost now and help keep the floor warm in the winter.
Bonus rooms also tend to be good candidates for radiant barriers in the attic above, especially if you have significant solar exposure.

Frank

[boardjnky4]

+1 for damper controlled zoning. We installed it at our house and it was a HUGE improvement.

[dmann]

Damper as in a manually adjustable damper or something with some electronics/smarts behind it? In our current house I know there are some distribution points up in our attic but being a 1.5 story I would need to be spider man to get over to the .5 story side of the attic and see if they had any adjustments.

I am meeting with the builder for the new house tomorrow and will grill them a little more about their setup. They did note in their Energy Efficiency features that they put extra insulation above the garage, so it sounds like they have at least thought about the insulation issues. I will ask what R-value they specify for this insulation.

Radiant barrier is a good idea too. I will consider this when picking a lot and determining southern exposure.

[fallingwater]

Interesting question, I am curious what other replies are going to be. A friend of mine owns a 2400 sft house in AL. She has two units.

[Donn2390]

Originally Posted by dmann

Damper as in a manually adjustable damper or something with some electronics/smarts behind it? In our current house I know there are some distribution points up in our attic but being a 1.5 story I would need to be spider man to get over to the .5 story side of the attic and see if they had any adjustments.

I am meeting with the builder for the new house tomorrow and will grill them a little more about their setup. They did note in their Energy Efficiency features that they put extra insulation above the garage, so it sounds like they have at least thought about the insulation issues. I will ask what R-value they specify for this insulation.

Radiant barrier is a good idea too. I will consider this when picking a lot and determining southern exposure.

The new damper systems are controlled in each room. If you have a room you seldom use, turn the tem off in that room. Each room has it's own thermostat. Turn of a room and a damper electronically closes. Great system, very expensive. We looked ito it for a retrofit. For our two system it was over $6k..! It would be cheaper in new construction
As far as one or two units, a lot depends on if it's one or two story. We lived in a two story 2800 SQ home with one system. it was very inefficent. Could never get the top and bottom floor equal. We now live in a single story 4000+ sq ft with two systems. We leave one system off during the daytime, and shut the doors to the unused rooms. One system controlles the end of the home with the bedrooms, so we shut the doors and turn off that unit in the daytime. Before bed we shut down the other unit, and turn on the BD unit for half an hour to warm the room, then shut it off for the night. Same plan durning the hot season, but in reverse. Saves a lot on the fuel bill..

[Chrisk327]

I don't know much about the damper systems. I do know what we did, which was what the HVAC companies recommended to me.

We put in 2 systems, one up one down, 2 compressors 2 air handlers with actually 3 thermostats. We are a 2000 sqft colonial with a vaulted entryway.

Basically I was told I could do it in 1 system and it might be a little cheaper, but doing 2 systems is the better way to go for easier controllabilty of temp between floors.

we actually have the additonal thermostat for heat, according to our plumber and confirmed by our AC guy, the Tstat in our hall works well for AC, as cold air sinks, but for hot air, since its open between floors etc, it will always be warm from the first floor and the second unit wouldn't kick on leaving the bedrooms cold.

[khuntrevor]

I would consider multi-split, duct free.