Multi zone HVAC? Help me understand
I have a 2 story house in MN, and I've got a question about making my HVAC setup a multi zone (main floor upstairs definitely, maybe basement). Currently, the furnace exists in the full basement, approximately centrally located. From the furnace, there are 2 main trunk lines that go in opposite direction and terminate with smaller round ducts (8?) that go perpendicular to the main line (toward the front/back of the house) and on to their final destination. The trunk is perpendicular to the joists (runs just below them in our unfinished part of the basement), and the feeder lines are between the joists. All are accessible where they branch off the main trunk. If I wanted to create a multizone setup (2, maybe 3 zones specifically), it seems that I'd have to add dampers to each feeder line (the 8 tubes I mentioned above), and then wire those into the zone control box. Both sides of the main trunk feed different parts of both zones. Using the current HVAC setup I'd need something like at least 11 - 8 individual dampers. I'd want the main floor during the day to be heated/cooled, and the upper floor to be heated/cooled more in the evening. Currently we heat/cool everything and the main floor is always either too hot/cold for the given season. Closing registers isn't really a realistic option as it's annoying to have to run around an open and close them. An automatic method would be nice. Installing the upstairs wired thermostat shouldn't be an issue. This leaves me with 2 questions: 1) Is this the correct thought process for creating a multi zone system, or would it be better to somewhat redesign the main trunk to better separate the individual feeders into logical zones to reduce the number of dampers? Does this make sense? 2) Can you wire multiple dampers into one zone? Thanks for your time! SkydiverMN First two story home should have two units! It just works so much better. You would be better off fixing what you have by fixing the duct work! 95% of jobs I see the duct work is not designed correctly sounds like yours is the same! Zone systems??? No way!! All your duct would have to be replaced for you to do this. Plus the added up keep and all the control issues, I'd fix what u have or add the 2nd unit I hardly doubt there's anything wrong with our ductwork, as everything works as expected with good pressure in each register. Keeping the house at any realistic temperature is easy and our gas/electric bills are not out of line for the given season. I'm simply looking for a more efficient way to heat/cool different parts of the house at different times based on our needs. Our house was built in 1969, has 2x4 walls, is 2000' square feet with good double pane low e windows all around. Our furnace is 5 years old and probably overkill at 100,000 BTU (98% high efficiency type), so I truly can't imagine the needing a second unit. Actually, even the idea that you'd mention that is pretty ridiculous. That being said, I do appreciate the comment, despite it not really helping or answering my question. Sorry best I could do! Just telling u the truth. With a zone system most all duct would have to be replaced First, zoned systems can be used in 2 story homes. The issue is addressed in Manual RS and Manual J. My house, 30 years old, is a two story home and originally built with one unit. At some point, an HVAC contractor installed a second HVAC unit dedicated to upstairs because he told the original owner it just works better The unit is 1 1/2 tons, the smallest split system they make. The footprint of my second floor is 450 square feet. Since I have owned the hosue, I have never turned it own and will actually be removing it. This house should have been setup using zoned and I plan to do so when my unit is replaced. Second, you do need to re-evaluate your ductwork. Its not an issue that your ductwork may be in bad shape. The issue is when you close 2 of your three zones, will your smalled zone be able to handle the total flow of the system or will it come apart. Further, will your system be able to work against the static pressure of putting all the flow through one third or less of the distribution system? Probably not. So for example, your system has 11 each 8 branches, lets assume 3 in the basement, 4 on the main floor and 4 on the top floor. When your basement and main level have no hvac call and you upper floor has a cooling/heating call, will your system (hvac and duct distribution) be able to deliver all the flow through 4 8 ducts for the full length of their run and not split the ductwork and/or freeze your coils? Regardless of yes or no, the quick fix to this is to install a bypass damper and avoid the situation. Now, for your house as descibed, I would do 3 zones minimal; Basement, First and Second. I would try to redo some of the ductwork to minimize the number of dampers required. Make sure you use Normally Open dampers so that they fail in the open position. This is better for your system in case of failure. Most zone controllers I have looked at for my house will not handle more than one damper but will provide some instructions on hook up a relay and transformer to operate more than one damper on a single zone. As a disclaimer, I am not an HVAC professional, but this should at least set you in the correct direction. Chris Airman, what is the upkeep you are refering to in the zone controls? The zone control board should have the same upkeep requirements as my main system control board and thermostats. Are you talking about have to replace the dampers as they fail? How often is this? I can see this being a problem if I had 11 of them or if my system often short cycled. But if I have three larger ones and the system is properly cycled to not short cycle, what will my upkeep be on a zoned control. Thanks!
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