Ducted or ductless?
user-6000307
| Posted in Mechanicals on
Hey guys,
Still working on my house specs for my 2800 sqft house just outside of DFW. I really want to have my ducts inside the conditioned space but this seems really difficult unless you foam the underside of the roof. So, I’ve seen these ductless units and wondering if it’s practical and maybe less costly. The big challenge, I think, would be the house is single story, spread-out and lots of rooms. Thoughts? I tried to attach the pdf floor plan but it failed. If you want to see the plan I can email, etc.
Thanks,
Shawn
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Replies
Shawn,
It's best to work with a designer who understands these issues from the start. Sorry to hear that contractors in Texas find it hard to keep ducts indoors -- I know about the problem, and it's frustrating. Contractors in Texas aren't used to basements.
You're right that ductless minisplits work best if you have a compact envelope. There are many reasons why stretched-out single-story homes are less efficient than compact two-story homes. (In a few weeks, you'll probably posting questions about how to solve a problem related to the distance between your water heater and a remote bathroom.)
If it's too late to re-design your house, you'll probably end up with ducted minisplits or a conventional forced-air system. If your house has 9-foot ceilings, it's a lot easier to build duct soffits.
The newish ducted minisplits are a pretty good answer, can be hidden above a closet to dump into two rooms
Fujitsu 9RLFCD
SZ-KD09NA
wish they were common when I was doing my house
Keith,
You could always install all/most of the required roof insulation as rigid foam board on the exterior of the roof decking. Maybe save some big $$ by using reclaimed rigid foam?
You could then keep your HVAC system in the now sealed attic space.
http://www.finehomebuilding.com/design/departments/energy-smart-details/an-unvented-superinsulated-roof.aspx
Depending on layout, mini-duct cassettes in closet-ceilng mounts can often handle up to 4 rooms with out soffited duct runs, not just a pair of rooms.
Getting to the "right" solution requires running preliminary cooling & heating load calculations on a room-by room basis. Sometimes adjustments in the location of partition walls, closets etc can ease ductless solutions. Don't leave it up to the HVAC designers to figure this out, but consult with a few on your goals, see if any of them are up for the challenge of getting it right when given some flexibility in the floor plan. They may have good suggestions as to where things might change to reduce the numbers of heads/cassettes, and locating them where service access is easy. (You DO want to be able to clean the filters and unclog condensate lines as needed.)
Ceiling cassette types under an air tight insulated dog-house in the attic with the insulation heaped over it can work too, often with minimal changes to the framing, if wall area is too precious.