[MattyBT]

I recently replaced my central AC and gas furnace with a full house mini split system, but we utilized a Mitsubishi air handler to take advantage of the existing ductwork so that we didn't have to add more wall units in various areas where the duct work did work well. (It doesn't work well for many areas of the house which is why replacing the central AC wasnt a viable option without tons of ductwork).

Would it be ideal to close off the ducts to the rooms that now have wall units? The wall units are significantly more efficient than the air handler, and it seems like it would be ideal to keep all the air flow to those parts of the house that actually need the central air handler. However, I dont know how to do this and I'm not sure if it would actually be helpful.

 

[ss120396]

Ideally the ductwork would have been disconnected and sealed off from the rooms that no longer needed it (presumably the rooms farther from the air handler), and the air handler would have been sized and commissioned to serve only the rooms that needed it. This would have reduced duct leakage and fan power, which means more energy savings.

In theory you could close off the register dampers in those rooms yourself, but it's hard to say whether this is a good idea - it would depend on the sizing of the air handler, the fan speed setting and whether static pressure would get too high with those rooms closed. At best it would mainly be a comfort thing, you wouldn't get the full energy savings of actually decommissioning that ductwork.

 

[MattyBT]

Ideally the ductwork would have been disconnected and sealed off from the rooms that no longer needed it (presumably the rooms farther from the air handler), and the air handler would have been sized and commissioned to serve only the rooms that needed it. This would have reduced duct leakage and fan power, which means more energy savings.

In theory you could close off the register dampers in those rooms yourself, but it's hard to say whether this is a good idea - it would depend on the sizing of the air handler, the fan speed setting and whether static pressure would get too high with those rooms closed. At best it would mainly be a comfort thing, you wouldn't get the full energy savings of actually decommissioning that ductwork.

The air handler was sized for only those rooms, but nothing was done to the ductwork. Would it be worthwhile to have them come out and disconnect/seal off the ductwork from rooms that are now conditioned by wall units?

 

[pecmsg]

Only the contractor that did the install can answer the question. We don’t know what’s there and what was there.
How many outdoor units how many indoor?

 

[MattyBT]

Only the contractor that did the install can answer the question. We don’t know what’s there and what was there.
How many outdoor units how many indoor?

2 Hyper Heat outdoor units split between the left and right sides of the house

Left:
6k - Bedroom
6k - 2nd Floor Left
18k - Air Handler

Right:
6k - 2nd Floor Right
9k - Converted Garage
12k - Sun Room

The house is 2 floors + basement.

The 2nd floor was running on window AC units because the vents did not work (two technicians came out from two different companies and very quickly decided they could not figure out why), so a 6k wall unit was placed in each room.

The main floor has a master bedroom/bathroom, kitchen + dining room, an office, converted garage, and sun room. The central AC adequately conditioned all of it except the Converted Garage and Sun Room.

6k in the bedroom so that I could cool it down at night without having to freeze the whole house.
9k head in the converted garage
12k in the sun room

The unit in the basement is the air handler and it is 18k.

The house was built in 1958 and is a cape cod style. All of the return vents are towards the floor, the 2nd floor had no return vents at all, and no returns in the basement, just vents on the ceiling.

If I were to close off some vents, I would close off everything to the master bedroom (has 4 vents towards the floor, I think two of them might be returns? 2 of the vents are directly adjacent to the door, and the other 2 are in the closet for some reason), close off the vent to the den/converted garage, and the vents to the 2nd floor.

 

[MattyBT]

Oh it's worth noting that the air handler has different pressure/fan settings.