Converting a single zone A/C system to a multi-zone? - AVS Forum
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post #1 of 11 Old 05-17-2005, 05:01 PM - Thread Starter
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Is is possible to convert an existing single zone heating/cooling system into a multi-zone system?
Is it even practical? What kind of cost are we talking about?
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post #2 of 11 Old 05-17-2005, 06:28 PM
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Yes, it can be done. It depends upon the layout of the system in the attic. The zoning unit is expensive. About $1000, maybe total install $1500?? I would try calling some AC companies to get an estimate. I am just guessing from my limited knowledge of zoned systems. I would do this if I had the budget, it is the best way, but I'm cheap and broke, so I just bought a $150 window unit tonight. Sucks, but I can always toss it later if money flys outta my hind quarters!

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post #3 of 11 Old 05-17-2005, 07:15 PM
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Since cooling was involved, I'll guess the system is forced air. That requires installation of a motorized damper for each zone as well as the associated sensors and controllers. If the ductwork is easily accessible and not many zones are needed, it can be very do-able. If the Ductwork is in wall and many zones are required, costs can skyrocket. Getting an estimate is really the thing to do as there are too many variables. A pro needs to be in your house to figure the possibilities.

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post #4 of 11 Old 05-17-2005, 07:24 PM
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I had 2 different HVAC contractors quote me for my attic to make it a 2 zone system using the existing 2nd floor system. The cost to add the dampers, run ductwork for the attic, 2 programmable thermostats and all labor was ~ $3,700. Both quotes were about $20 apart.....

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post #5 of 11 Old 05-18-2005, 01:08 AM
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I had 4 quotes done to convert our attic single zone system into a 3 zone system. Quotes ranged from $2000-$2400. We could have just gotten a new system for the new room, but that would be a 4th HVAC unit on the house. It was better for us to zone the existing upstairs unit. We are now able to set the thermostat in the guest rooms to high/low temperatures since they are rarely used and don't need to be heated and cooled unless they get too hot/cold. Also, the theater is not used that often so it can be set to high/low temps and then set to comfortable temps for times when it is going to be used. Essentially, we were able to lower the HVAC use in lesser used rooms by converting to a 3 zone system.

There are no stupid questions, but there are a LOT of inquisitive idiots. Me being one of them at times.

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post #6 of 11 Old 05-18-2005, 08:07 AM - Thread Starter
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Thanks for the replies. This gives me an idea of what to expect when I get a quote.
Our house might be considered on the small side so I'm not sure if we would need more than 2 zones. One for the HT (basement) and 1 for the rest of the house (1st and 2nd floors). The more zones the better, but I guess I'll have to see how the estimate comes out.
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post #7 of 11 Old 05-18-2005, 08:53 AM
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You might want to consider a 2-zone solution with the first floor on its own zone, and the basement and 2nd floor on a second zone. The heating/cooling needs of the basement are slightly closer to being in line with the 2nd floor of the house than the first floor.

With zoning, you have to be careful about the static pressure in the ductwork when only one zone is calling for heating or cooling. If the static pressure is too high, you can run into a number of problems; automatic humidifiers may end up spraying water, your air handler (fan) may become damaged, or the refrigerant in your cooling coil may not completely vaporize and you can end up passing liquid into your compressor (due to air that is too cool already when passing through the cooling coil). This can cause a compressor to literally shred itself via a circumstance known as "slogging"...

Zoning needs to be designed/installed by a professional who understands how to do it properly. Many pros are not expert in zoning and can produce a real mess for you. So, get references and check them out!

Good luck,

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post #8 of 11 Old 05-18-2005, 10:17 AM
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Quote:
Originally posted by dwightrahl
The heating/cooling needs of the basement are slightly closer to being in line with the 2nd floor of the house than the first floor.
Huh? The needs are radically different. The worst case is on a sunny summer day when the basement walls are next to the cooler earth while the summer sun is adding heat to the air warmed top floor. Additionally, the convection favors cooler air descending while warmer air rises.

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post #9 of 11 Old 05-18-2005, 10:22 AM - Thread Starter
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Dwight,
That is interesting. I would think the basement and 2nd floor would have almost opposite needs. In the summer my basement stays relatively cool even with the A/C off while the 2nd floor is blistering. You know the whole heat rises and cold air falls.
In fact, with my current setup down there (the whole basement is open), I could probably get by without ever running the air. I'm just worried that once I seal it up and put a projector and people in the room it will heat up fast.
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post #10 of 11 Old 05-18-2005, 10:38 AM
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Quote:
Originally posted by greywolf
Huh? The needs are radically different. The worst case is on a sunny summer day when the basement walls are next to the cooler earth while the summer sun is adding heat to the air warmed top floor. Additionally, the convection favors cooler air descending while warmer air rises.
I agree.... a basement requires very little heating or cooling, compared to the rest of the house, and especially a 2nd floor that most likely has a very hot or very cold attic above it (depending on the time of year).

In speaking to the HVAC contractors I had to my house, they both said they would build a new exhaust plenum on the existing fan unit and build a bypass into the system. That way, the motor and coils are still seeing the proper flows and aren't working any harder. If you try and stuff twice the amount of air into the same duct, the motor works a lot harder, is less efficient and the coils are as efficient either.

Just my 2 cents...

Jerrod

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post #11 of 11 Old 05-19-2005, 06:23 AM
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Hi Greywolf,

I can only describe how the temperature situation has worked out in my home.

I have my basement (where the theater, a playroom, and my office are) and first floor on one zone, and the second floor on a separate zone. In the winter, the first floor calls for heat more frequently than the second floor does (due to heat rising naturally from the first floor to the second). This has the effect of warming up the theater dramatically in the wintertime - so much so that I've had to open up the door at times to let the warm air out of the theater.

I have a mini-split heat pump in the theater, but I haven't had a low-ambient-temp kit installed on the outdoor unit, so I can't use it for cooling during the dead of winter.

During the summer, the second floor tends to call for cooling a little more frequently than does the first floor. I say only a little more frequently because my house is very well insulated (r60 in the 2nd floor ceiling/attic, and 2x6 exterior walls with r19 insulation). The theater would tend to get a bit cool when not in use in the summer if tied to the 2nd floor's heating/cooling needs, but that can be easily mitigated by the heat generated by the PJ and people during a film, and if necessary, I can make heat with my mini-split heat pump during the summer. Being tied to the first floor's heating and cooling needs has been OK for the summer months, but I have still had to augment the cooling in the theater with my mini-split during movies.

I live in NorthWest NJ (rather cold most of the winter, really hot for only a few weeks during the summer); so for other areas of the country, a different solution might very well be needed.

Jerrodshook,

Sounds like your HVAC guys know how to deal with the static pressure issues that arrise when zoning isn't done properly (assuming that your air handler isn't a variable speed one - if it is, you don't need the bypass at all because the fan will automatically slow down in response to an increase in pressure in your ductwork). Just make sure that they are planning on using a pressure-operated bypass damper rather than a manually operated one. Don't laugh - I had one HVAC contractor try to pull that one on me...

Good luck,

Dwight
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