Dual zone mini split
 

Well, not exactly dual zone. I would like to use a single outdoor unit with downstairs wall unit for heating and an upstairs wall unit for cooling.

Our house layout is open between the two floors. The basement stays cool with only a window shaker upstairs in the summer. In the winter we need to heat the basement and the upstairs stays warm from convection.

Rather than buying a two-zone system I would be perfectly happy if I could switch the zones manually each spring and fall. Just a few ball valves and switches should do it.

Anybody see a problem with this?

Most true multi-zone systems have a lower turndown ratio than single zone systems. if you choose a dual head setup, make sure that doesn't affect you negatively.

The problem I see is the refrigerant and oil trapped in the closed off section. for it to work well, I believe you'd need to "pump down" the circuit you aren't using. otherwise you have will have little control over how much refrigerant is where, and will likely lose capacity.

if you proceed, you would want to make sure you don't trap oil in your manifold, and be sure to choose valves and piping rated for refrigerant use.

have you considered two single systems? that would get you some redundancy as well, while maintaining simplicity, not to mention warranty support wouldn't be compromised (assuming this matters to you - on a really hot/cold day, it might).

I forgot about those issues in spite of reading many previous discussions to that effect. Thanks for jogging my memory.

Since I am primarily interested in lowering my winter bills I think one unit downstairs would be a good place to start.

Doug