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I have a three story brick duplex built in 1925. There is currently no ductwork (steam heat) and I doubt that it's feasible to install. Windows are wooden double hung with storm glass, they are in fantastic shape and I'm not particularly interested in replacing them.

Unfinished basement, 1st and 2nd floors are all 1380 sq ft, but I'm not concerned about conditioning the basement. 1st and 2nd floors have 3 bedrooms, living room open to dining room standard doorway to kitchen. 3rd floor is 690 sq ft split into 2 rooms.

Given the steam heat, I only need splits that provide A/C, I assume these are cheaper? If not, can you totally shut down the systems through the winter when not calling for heat? I've seen there there's some standby power draw, but can that be avoided?

I need at least two different systems since the 1st floor is an independent rental unit.

Special considerations:

  • We're in a zone 6 climate (used to be 5, but "they" recently changed it)
  • The south west room on each floor is particularly susceptible to solar gain due to a lack of shade.
  • My wife likes to bake, so the oven is frequently in use.
  • For my family the all the bedroom doors are usually closed because the children like their privacy and the 3 year old gets into things.

Given all the non-optimal factors does it make sense to put a heat exchanger in each bedroom? Assuming the kitchen should be cooled that would mean a 5 head system on the 1st and 2nd floors, and a 3rd 2 head on third floor. That seems like overkill, but I'm not sure how I'd cool all the rooms with the doors shut.

9,000 Btu/h is the smallest head available on the system I'm primarily looking at. So it seems like I'd be looking at 9-9-9-12-12 = 51,000 Btu in potential total draw, but in reality the max load is more like 39,000. The condenser with this system is actually 42,000 btu so you can't run every head full out, but I'm not planning to.

tl;dr - Here's the actual questions:

  • If I don't need the heat is it worth looking for a mini split without the heat feature? These seem harder to find
  • If not using the head feature can you avoid standby power consumption?
  • Is it totally crazy to have 5 heads and 51,000 btu of cooling (backed by a single 42,000 btu condenser) in six rooms totaling 1,380 sq ft.
  • Is there some better solution I've somehow overlooked? The house came with an assortment of window units, but there don't seem to be appropriate (grounded) outlets near the windows they would make sense in.
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The way to go here is definitely the ductless mini splits. It sounds as though you have done your homework on this and you can always find what we call straight cooling units without heat. The mini splits are far more efficient than nearly any other system these days and you can choose which room you need to cool and how much it needs and when.You'll be glad you chose to go this way after its done.As far as stand by power, just unplug or turn off a breaker, but its not a lot of power loss either way. As far as over kill, you'll be glad if you add some overkill to an old home, they usually need it unless they are very well insulated and have great windows. Just speaking from experience.....good luck.

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You can avoid standby power by turning the breaker to the system off. You might find that the split system is cheaper to run as some rooms on the upper floors require much less heat and can be adjusted to the occupants comfort. Some of the early ductless system were AC only but just a simple change (reversing the system flow) turns it into a heater so the cost difference is not that large for the benefit. I would also check into tax credits and or rebates from your power company for installing a energy efficient split system in some areas these can add up to several thousand that can make the unit more affordable.

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You can surely get A/C-only split systems; install one in the wall of each area you want cooled. They are quieter, more powerful, and far less ugly than window units. Keep in mind that the peak BTU/hr rating just sets the speed with which you'll reach the desired room temperature; the units should run at much lower power draw when maintaining temperature.
It is true that modern heating/cooling systems are set up to run off a single thermostat, but that's hardly necessary (more of a spiffy feature).

Switching to a head + cooling new system is likely to be expensive, since now you need systems to handle every room.

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