Adding another HVAC Zone

handy man88 · 10-09-2007, 10:37 AM

If a home has only 1 zone, how hard is to to add another zone?

House that we are considering buying is a standard colonial style with a finished walk out basement. Gas heat, electric cool.

I want to possibly segregate the 2nd floor as another zone, with gas heat. This probably means a gas line would need to be run to the attic, if one does not exist already. I know flex piping is sometimes used to run gas lines, but does code dictate only for a short distance, otherwise cast iron is required?

Other issue is ducting. It's not hard adding dedicated ducting to the 2nd floor, but how would they seal off the 2nd floor service from the main unit? Would I need to replace the main unit b/c it may be oversized if it now only needs to heat/cool the 1st floor and basement?

Is this normal or common for HVAC techs to add another zone to a house without major demolition?

scorrpio · 10-09-2007, 11:24 AM

How is your ductwork currently configured. Usually, coming out of air handler, the main supply splits. One branch runs in the basement, supplying 1st floor registers, while other branch rises to supply 2nd floor.

What do you do:
1. Install motorized dampers on both branches
2. Install a zone control panel. Wire it to the dampers.
3. Wire existing 1st floor thermostat to zone control panel.
4. Install a thermostat on 2nd floor, run a wire to zone control.
5. Wire zone control into your furnace/AC.

When either thermostat calls for heating or cooling (in the unlikely event thermostats are making conflicting calls, "first come, first serve" method is used), zone control signals the HVAC equipment and opens dampers to all zones requesting that type of conditioning.

One place to check:
http://www.retrozone.com/

Should be a whole lot cheaper and easier than installing a whole new HVAC system in the attic.

handy man88 · 10-09-2007, 11:31 AM

Quote:

Originally Posted by scorrpio

How is your ductwork currently configured. Usually, coming out of air handler, the main supply splits. One branch runs in the basement, supplying 1st floor registers, while other branch rises to supply 2nd floor.

What do you do:
1. Install motorized dampers on both branches
2. Install a zone control panel. Wire it to the dampers.
3. Wire existing 1st floor thermostat to zone control panel.
4. Install a thermostat on 2nd floor, run a wire to zone control.
5. Wire zone control into your furnace/AC.

When either thermostat calls for heating or cooling (in the unlikely event thermostats are making conflicting calls, "first come, first serve" method is used), zone control signals the HVAC equipment and opens dampers to all zones requesting that type of conditioning.

One place to check:
http://www.retrozone.com/

Should be a whole lot cheaper and easier than installing a whole new HVAC system in the attic.

I have no idea how the ducting is wired up, as I didn't think to look at this issue when I visited the house. But, thanks for the great suggestion about the dampers. I hadn't thought of it.

I did see space heaters in the basement though, so I wonder if there's a heating issue. Home was built in 1993, and I guess zoned heating/cooling wasn't as popular then.

dmaceld · 10-09-2007, 10:45 PM

Where are you located? That will make a big difference in how you tackle this. One issue to watch for, if you add a second unit, is sizing and balancing. Warm air rises, so the first floor unit can carry the bulk of the heating load. Cool air drops so the second floor unit can take care of the bulk of the cooling load. That right there can create size conflicts when you select the unit to install.

Make sure whoever HVAC contractor you use, that he does heating and cooling load calculations by the book, not by rule of thumb. If he says, "Oh, we always put in a ton of cooling for every 400 sf of floor space," or, "We always install a 100,000 Btu furnace in a house your size," lose him as fast as you can.