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  1. #1
    Join Date
    May 2005
    Posts
    74
    Getting quotes for my 2,900 sq feet split level house. I just put a 650 sq feet addition on over the garage. The outside is 3.5 tons and air handler in attic is 5 tons. I thought I wanted two units - one for the upstairs and force the existing unit to cool the downstairs.

    One contractor said that adding zoning costs more than I can ever recoup in energy savings.

    Another contractor said that the Carrier Infinity is the best at zoning and it would be possible without costing too much more.

    I have read through many posts but I have not found one that gave me a simple overview of zoning with one system and how it uses dampers and a variable speed air handler.

    Here are the facts: I want two zones - one for upstairs and one for the small "middle level" and downstairs of the split-level home. I guess that when I open the upstairs thermostat, the damper electronically closes the duct(s) that feeds the entire downstairs (typically, is there one duct or multiple ducts that feed downstairs?). If I open the downstairs thermostat, the damper closes the duct(s) that feeds the entire upstairs. Obviously, when both thermostats are opened, the dampers open up and the full 5 ton unit is blasting throughout the whole house.

    Let me know if I'm wrong on that understanding. That brings me to my next question - how does a 5 ton unit uses less tonnage when only one zone is being called for (to avoid short-cycling)? Does the variable speed air handler come into play? Meaning, if only one zone is used, the variable speed air handler would go on low speed (hopefully enough the cool the one level). Obviously, if both zones are used, the air handler goes on high speed (no speed in between?).

    That brings me to my last question. If I have a central return installed in the upstairs hallway (currently on the slanted ceiling above the staircase), can that be used in a two-zone system? That is, if I just want to cool the downstairs, the one central return will pull the hot/humid air from the downstairs to the upstairs hallway? Or does another return have to be installed?

    I thought this would be a good post to cover some of the basics that other newbies might not be aware of. Your thoughts would be much appreciated on this.

  2. #2
    Join Date
    Jun 2005
    Posts
    83
    The Carrier or Bryant zoning system works nice with the infinity zoning system. Can control the speeds on their air handler or furnace. The infinity can control a two speed condensor, two speed furnace, humidifier, with the zoning it can control dampers. This is a nice control system that contractors can work with.

  3. #3
    1. it will cost more to install a 2nd system than a zoning system
    2. it will cost you more money to service 2 systems than one
    3. you will pay more for electricity for using 2 systems over one.
    4. most residential contractors do not understand zoning systems so you will have more contractors giving you false information about zoning. just because 5 contractors say one thing and one says another does not make the 5 right.

  4. #4
    Join Date
    May 2005
    Posts
    74
    Anyone on whether one central return can be used on a zoned system?

    Also, does variable speed come into play when only cooling one level?


  5. #5

    Zoning

    Airworx is 200% correct in his statements. Now the question of does a variable speed blower come into effect on a zoning system? Only if you are installing the Infinity Carrier Zoning System. If you don't use that system, you will be installing a bypass damper to limit the air capacity. If you are using a two stage cooling and two stage heating system, you save considerable energy with a zoning system. If you use a single stage cooling and a single stage heating you save a little over two units, but not dramatically. As for the central return air grille with a two zone system, it depends on its location and size.

  6. #6
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    crt, are you including the Trane integrated zoning system ("IZS")in your assessment? My understanding is that the IZS when used with the XL19i does control a variable speed fan. At least that's what I've been led to believe by the Trane distributor, dealer and participants on this forum.

    I also seem to recall that the Lennox Harmony zoning system controls the VS fan.

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by mxylplik2
    Anyone on whether one central return can be used on a zoned system?

    Also, does variable speed come into play when only cooling one level?


    One return is fine for two zones,IF it's inthe middle of the two zones,so that that it returns the "calling" zones air without affecting the temperature of the other zone.


    That said ,all rooms with doors,need a return air "Path",or the dors need to be let open.This becomes more important with zoning systems.

  8. #8
    Join Date
    May 2005
    Posts
    74
    [/B][/QUOTE]


    One return is fine for two zones,IF it's inthe middle of the two zones,so that that it returns the "calling" zones air without affecting the temperature of the other zone.


    That said ,all rooms with doors,need a return air "Path",or the dors need to be let open.This becomes more important with zoning systems. [/B][/QUOTE]

    So if the return is in the upstairs hallway, it wouldn't be in the middle of the two zones. But if the return is in the ceiling above the staircase, it would be in the middle of the upstairs and the downstairs. I would imagine that the return will still suck air from both levels even if only one zone is operating, so I'm not exactly clear how that would that affect temperature in the other zone if the supply registers are blowing only in one zone.

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