[Jaxx]

Hello,

I need an all new HVAC system and I was thinking about installing a system with variable speed motor and zoning (+bypass damper).
Does a setup like this including zoning make sense in a single story, 1100 sqft, 3 BDR house, especially if 2 of the 3 bedrooms are mostly not occupied?

Thanks!

 

[user_12345a]

A sensible way to zone would be to put all the bedrooms on one zone and the living space on the other.

If you want fine control over each bedroom, skip the ducted forced air and put in a mini-split system. In single story zoning is tough to justify.

If you value efficiency, don't put in a system with a bypass. You need 2-stage equipment so that when one zone is calling the capacity/airflow match, with both stages only being allowed to come on with 2+ zones calling.

I imagine the ducts would also have to be oversized, because first stage on multi-stage equipment is 60-70%+ capacity. The smallest zone would need to be able to handle all the airflow on first stage.

The builder better have a damn good hvac sub if you want zoning done right.

I see you're in california - best investment would be to have the roof deck insulated and make the attic space a semi-conditioned space with a real floor. Use sheet metal ducts, not flex. In a new house it may not cost that much extra, and ammortized over 20+ years the energy savings could offset the higher mortgage payments.

 

[Jaxx]

A sensible way to zone would be to put all the bedrooms on one zone and the living space on the other.

If you want fine control over each bedroom, skip the ducted forced air and put in a mini-split system. In single story zoning is tough to justify.

If you value efficiency, don't put in a system with a bypass. You need 2-stage equipment so that when one zone is calling the capacity/airflow match, with both stages only being allowed to come on with 2+ zones calling.

I imagine the ducts would also have to be oversized, because first stage on multi-stage equipment is 60-70%+ capacity. The smallest zone would need to be able to handle all the airflow on first stage.

The builder better have a damn good hvac sub if you want zoning done right.

I see you're in california - best investment would be to have the roof deck insulated and make the attic space a semi-conditioned space with a real floor. Use sheet metal ducts, not flex. In a new house it may not cost that much extra, and ammortized over 20+ years the energy savings could offset the higher mortgage payments.

Thanks for the feedback.
The house doesn't really have an attic. The roof is low sloped and the roof is the ceiling in all rooms. Only the hallway along the center of the house has a low crawlspace-type attic in which all HVAC duct will need to be run.
I was planning on using sheet metal duct even thought that attic space is super tight and it will be really hard getting that stuff in there.

BTW: No builder - all me:vs_wave:

 

[gregzoll]

Hello,

I need an all new HVAC system and I was thinking about installing a system with variable speed motor and zoning (+bypass damper).
Does a setup like this including zoning make sense in a single story, 1100 sqft, 3 BDR house, especially if 2 of the 3 bedrooms are mostly not occupied?

Thanks!

Leave it as is. You will end up with those other rooms showing signs of mold and/or moisture, if they are not kept conditioned like the rest of the house.

It is a old myth that people think shutting vents off in rooms that are not used, is going to save them money. It does more harm then good.

Zoning is good if you are say using one room for a Home Theater and do not want the heat running while in there, or want to cool that room off, but do not want to cool off the rest of the house, unless there is a call to the zone controller.

You will not notice any cost savings difference if you go around closing vents. But you will notice an increase of output in those areas that may not have great airflow CFM coming out of the vents.

 

[Jaxx]

Understood.
But I can still use a variable speed air handler, I assume?

 

[beenthere]

To zone in a small home of 1100 sq ft, single level. You would need to use a better zone panel then the what is commonly used. And you will need either a bypass damper. Or the dampers to all zones must be set to bleed some air to them when they aren't calling.

For the zoning panel, an Evirozone panel. W8835A1004U, uses communicating thermostats, and is an auto mastering panel, and only the master zone can bring on the heat or cooling. Prevents short cycling so its easier on your furnace.

Plus use Truezone dampers. These have adjustable range stops. So you can set up enough bleed that you may not need a bypass damper.

You can always use a VS blower, no matter how small or large a home is, or whether or not its zoned.

You won't be able to shut off the unused bedrooms. A single bedroom in a small house would be to small to be its own zone if it were ever able to call for heat by itself.

Zoning isn't always about saving on heating and cooling cost. Often its just about having an area your in at the temp you are comfortable at.

 

[gregzoll]

Understood.
But I can still use a variable speed air handler, I assume?

That is what I have for my furnace. Majority of the time it runs at Stage 1. Rarely does it kick into Stage 2, unless we have had a really cold day or a really hot day.

 

[yuri]

If you live in California heating is not a major issue. AC is. I would get a 2 stage 80% efficient furnace with a ECM Variable speed (not X13) type fan motor. Will give you better AC as it can dehumidify better plus it uses less elec $$.