single vs/ dual zone central a/c

[tran92]

we're in the process of getting quotes for a new central a/c system. (ours is 18 years old now)

currently its a single zone for a colonial (4 ton system)

our big question, is it worth it to split this system into 2 zones?

the first company we asked gave us a price quote and said they would just redo the ducts in the attic to make 2 separate lines, one for downstairs and one for upstairs and use dampers to open and close either system. the cost was 2100 to add the new ductwork and dampers.

we got a second quote today, and this person said no way, not to use the dampers as they could be points where moisture could build up in the system, and that there would be too much air into one zone (since its a 4 ton unit) and we would have to have the extra air released someplace, which is a waste. He said we would not save any money on electricity if we split the zone (although he did also mention the variable speed control so that the 4 ton unit could start up as a 2.5 ton unit, which would seem to be lower the air flow through the single zone, but anyway)

the question is, are the dampers a problematic piece in the system? do they break down alot? could we end up with moisture in the system?

and the big one, will we save any money by splitting out single zone at all, using dampers? if it will cost the same for electricity to run the unit, we might as well leave the single zone and save 2100, but if it will help with the bills we would consider splitting the the system to 2 zones.

Can anyone give us some advice or better explanations for what we were told?

thanks alot

Amy

[browntigerus]

Zone system do work....

If you have temp imbalance btw 1st and 2nd floor, zoned it could cure it. Zoned is the only way I can have basement heated w/o replacing furnace....

For 2 stage untis zoned system can be set to call 1st stage if only one zone is making call for heat / cool.

>not to use the dampers as they could be points where moisture could build up in the system

Dampers not 100% closed, they set to bleed. Not seen much moisture on mine....

> and that there would be too much air into one zone (since its a 4 ton unit)

Could be true if one zone 500 sq ft and another 2500 sq ft.

> and we would have to have the extra air released someplace, which is a waste.

Not very true. Zoning system could have bypass, bleed 70% closed, dump zone or even all together. Dumping air into two story entry inside of your house is not a waste. Sounds like he did not have training, experience or both.

>are the dampers a problematic piece in the system? do they break down alot?

So far I had one honeywell damper failed, some suggest EWCs.

>and the big one, will we save any money by splitting out single zone at all, using dampers

How could one tell? Depends on how you are using it. In my case 3 zones: 1st, 2nd, basement. Savings come from not heating or cooling basement, somewhat less cooling / heating house.

[Irascible]

You might save a little on your bill. As brown points out, it's difficult to prove. The real reason to get your system zoned is for even comfort. However, a properly designed zone system is a rarity in my opinion. It's so rare that I advise people against them unless they have a rare contractor.

This may be a little more than you want to digest now. But I wrote it to explain the challenge of a zone system:
http://hphaa.com/services/installati...m#Zone_Systems

[beenthere]

Zoning is more for comfort then saving.


If you use set back stats you will see some savings from zoning.

The dampers won't sweat. If they install them in the attic, they should insulate the sude plate where they have the damper installed.

Yes damper motors can fail, so can A/C fan motors.

We use EWC mostly. But have recently begun to use Arzel also, and both are good brands.

You can use a bypass damper with most zoning systems so as not to dump the air you just paid to condition.