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I have a 2000 sq ft house in TN(mostly air-conditioning is used, winter is mild) and the house has 2 trane gas furnace for heating(both 25+ yrs old) that need to be replaced, one 25+ yr old air conditioner that needs replacement and one fairly new Trane air-conditioner. I just want to go with a ductless 6 zone mini split in the whole house for both cooling and heating. One to save energy(most of the time we keep windows open, 6 months out of 12 i would say), rest of the time we often want individual control in rooms hence lot of energy wasted in traditional systems. Secondly, I have allergies and I really hate filthy ducts. The cost to replace all the ductwork and all HVAC is also quite expensive.

The only challenge I see is that cost of Daikin 6 zone is around 6-8k but I am hearing that installation will be quite high so any advice on that? And if I go this route, is it easy and cheap to just remove old duct work and seal whatever needs to sealed properly?

On same lines, considering to put a hybrid heat pump water heater in garage also.

ns12345
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    "I have allergies" - you'd have to tell me then. Is it better to have forced air with a filter, or not? And have you ever had a TFP? (Turbulent Flow Precipitation). - Can't have either of those w/o whole house forced air. Well, you can but.... - "save energy" usually just means all the stuff costs more. Pay for comfort, not efficiency. Which one do *you* WANT? – Mazura Feb 28 '22 at 02:00
  • Na, I use air filters - def helps. But i think i really like ductless environment better, just seems better than forced air. I think colder weather regions need heat on gas for affordability that's a mjor reason to centrally heat as well as cool. But may be I'm wrong, seems like waste of energy too. I want best utility for my scenario like i want to set my own temperature in my office vs rest of the house etc. But you're right, trade-offs! – ns12345 Feb 28 '22 at 02:42
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    A good minisplit head **has** filters - nice washable electrostatic ones on mine. – Ecnerwal Feb 28 '22 at 03:36
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    Watch out for heat pump water heaters. They steal heat from the room they're in, making that room colder. If you don't do something to put heat back in the room, they get less and less efficient. In the winter: just shifting the cost of heat. In summer: free A/C. – Harper - Reinstate Monica Feb 28 '22 at 08:07

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One of the biggest benefits of going with all ductless mini-splits is that every room can be controlled independently. If you aren't using a room, you can shut off the climate control in that room. This can translate to major energy savings, depending on how you use the rooms in your house. Additionally, in many houses the ductwork snakes through the house in ways that cause significantly restricted airflow, which is not a concern with ductless units.

On the other side of the coin, one of the biggest downsides of going with all ductless mini-splits is that every room must be controlled independently. It means you need to keep aware of what the rooms are set to, and remember to change all of them when you need them changed. Different systems have different rules they follow when some units are calling for heat while others are calling for cooling. Some units, such as those made by Daikin, can have a WiFi module installed (in each indoor unit) that will allow you to manage all the rooms from an app in addition to the remote control, allowing you to change all of them at once. Others, such as Mitsubishi, have other network capabilities, but I don't know the details.

In terms of installation costs, those depend very much on your local market. You'll have to get quotes from local installers. You don't need to remove the ductwork -- that will almost certainly be very expensive, just seal it off and leave it there. The simplest seal (on the room end) would be a magnetic sheet like this, but that doesn't look so nice and it only works if your vent louvres are pretty flat. A nicer option would be to remove the louvers and patch the wall. Either way, you'll probably want to put some kind of fire-blocking inside the duct so that fire can't spread easily from room to room. You'll also want to make sure you seal up the furnace (trunk) end of the duct, which you can probably do easily with the same sheet metal the duct is made from.

One other possible downside of a ductless system is that it is typically cost-prohibitive to install an indoor unit in hallways or bathrooms, necessitating that those rooms are heated/cooled by other means (or by spillover from the conditioned rooms). One way around this is by breaking up the existing ducts into smaller groups and having some of your indoor units be ducted instead of ductless so they can handle more than one room. However, that's going to be a lot more expensive to set up.

Despite the potential downsides, I would be inclined to lean toward the mini-splits in your situation.

Moshe Katz
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