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I saw a video where Richard talked about mini duct A/C. I have a split level house with hot water baseboard heat so no furnace. Is it possilbe to still use mini duct A/C. How would you do it with no furnace to connect to?
He's probably talking about mini-splits. These still have a small outdoor condenser and copper lines to a inside unit. THe difference is that the indoor unit is either mounted to the wall or a flush mounted unit in the ceiling.
The main advantage is that some models can run multiple indoor units so you can have 2, 4 or even 8 zones on a single outdoor unit.
Samsung, Fujitsu and Mitsubishi, IMO make the best units.
There is also a small diameter heating/cooling system - - - one is "Unico" which you can google and I believe Richard Thuhe the TOH HVAC/plumbing guy also has a video in the TOH site where he talks about after seeing it in a trade show.
I've seen Unico systems in California for flat roof modern houses w/o duct work. The system uses a small diamter flex tub - about 3" diameter - (and flat tubes on a roof) with 2" dia. outlets. The tubes, being small diameter, can be routed through many spaces and air flow is high velocity (Unico says it's quiet at the 2" outlets).
Richard thinks the system serves well any house that doesn't have duct work. My limited research on it is that it relatively expensive both to re-capture R&D costs on the concept and that installation is still labor intensive. In California, a flat foam roof and Unico was typically priced at $30,000 (knowing a foam roof is about $15K, the Unico appears to be $15K, and that's for mounting flat tubes/channels on a flat roof plus Heat/Cool hardware). If you have to snake 3" tubing all over a house, the labor is way more. I've seen it mainly as a cooling A/C system and for heating for additions & add-ons (everybody seems to have heating)
The mini-split, also know as ductless A/C, is great for cooling big, open spaces but if you want to have air handlers in several rooms, the cost will pile up. I haven't research mini-split in several years, but I understand a single outdoor unit can have up to 8 air handlers (32" x 8" evaporator boxes) - I'm used to seeing 2, with 3 max in Calif. A system for 2 handlers is $5-6K in California.
I think there is a separate beast known as a mini-duct, which is essentially a mini-split with short ducts. It doesn't need a furnace obviously, just a mounting space and the ducts can be snaked/routed to an adjoining room say.
You'd mount it in an attic (assuming you have one) or similar space. Similar to the Unico System or ductless. If you have attic space, it might be possible to install a conventional ac system too - I've heard they can be cheaper than the high velocity small duct systems.