Closing vents is not efficient. Your HV should be designed to run ”open” if you decide to upgrade to A/C, expect to repace the existing heater, plan to spend $10k, and please read the instructions.

Assuming your priorities are economical cost for initial installation and low energy consumption, my thoughts are. Your ducts are probably metal,consider keeping them because 60 year old metal duct will usually still be in excellent condition,transfers air more efficiently than modern flex-duct and will still be working when flex has deteriorated and falling apart. If heater is from 1963 it would be wise to replace it at same time as adding cooling. You don't need to replace duct to qualify for rebate incentives,just make sure insulation is intact and reinsulate as needed.

To answer your question(s) about closing vents in rooms not in use, there's multi-speed,multi-zone systems that do it automaticlly "IF THE INSTALLER UNDERSTANDS HOW TO INSTALL THEM" otherwise the system will be ineffecient,require repeat service calls and unending pita.. Closing vents on conventional system can work but there's another solution you might like better. Electrically controlled dampers can be installed near air handler and operated by wall switches and/or timer. If choosing to manipulate airflow of conventional system don't oversize equipment because that can sometimes cause poor humidity control. If retaining old ducts it might be neccessary to add another duct to bedroom wing and another to living wing so that equipment can breath. Regardless of type equipment installed , if installer isn't compitent, honest and willing to work with you it's a losing game.

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Hi, John,

The title of your post "Central Air Conditioning versus...?" suggests you'd like to explore alternatives to a forced-air central air conditioning system. I suggest you take a look at ductless mini-split heat pumps. They are much easier to retrofit in an existing home and provide as many zones of independent temperature control as the number of cassettes installed.

Thank you for the replies. What are the general costs? The electrically controlled damper thing versus ductless mini-splits?

The mini-split thing was seeming like a good idea, but then I found a page stating that a mini-split system for a full house would be in the range 5k to 8k per zone, 20k or more overall. Yikes.

Dampers and controls add $300 - $500 each to a new system using old duct,$200 to $400 each with new ducts. I can't speak to what local contractors charge to install mini-splits but the average labor is 4 hours for a single head system,add 3 hours for each additional head.