Installing central air in older house, where to start?

Thanks

You may want to research what is called a "Manual J" calculation. There is a lot of info on it on the internet. It basically calculates how much cooling capacity you need for your house.

Here is one site about it. I have not looked over the program and know nothing about this particular one. You should be able to find many more if you search for Manual J.

I do a lot of home repairs and auto repairs myself. I even put in a replacement furnace and AC. But outfitting a house that never had a system installed, I wouldn't do that. If you have the right skills, tools and most importantly experience, I think you're going to have a much better result in a small fraction of the time than if you try to cobble together all the necessary duct work yourself. As for sizing, when I looked about 8 years ago, the calculation tools were available, but you had to pay a substantial fee for them or to use them, etc. Also not sure how user friendly any of those are for the novice. I think most pros don't use them though, they just use their experience and wing it. Having said that I would not DIY, I have also seen really screwed up installs by pros, where for example the upstairs can't be adequately cooled. With one level and a basement your install should be straightforward and harder to screw up.

You might want to look at the new high velocity AC systems they have now. Those use smaller ducting, like 2" flexible that move air at high speed. I think the tradeoff is they are much more expensive, but then the install for DIY is likely much easier. But you may also find that you can't buy the eqpt for that. That's a problem with DIY with HVAC, you will be very limited to what brands you can buy online or that will sell to you locally. The only brands I know have been available for DIY are Goodman and Rheem. I went with Rheem, overall I'm very happy with it. Even there you have drawbacks, eg probably no warranty.

I live in the land of ranch style houses and the duct work is always in the attic. You may have to give up a closet for the air handler if you are not willing to build an insulated "house" for it in the attic. You may want to go another way tho. A mini split system is actually becoming the choice these days for retrofits in houses with no ductwork. You can get them with several "heads" and you only have to run the line sets. They use inverter style condensers that regulate the condenser speed to the number of heads calling for cold air so they end up being far more efficient than traditional systems. I would avoid the "cassettes" (ceiling mounted units) because they require pumps to get rid of the water. Use wall units wherever possible and send the water out through the wall. There is less to go wrong. Your line sets can go through the attic. Just protect them from damage with 2x3 framing on both sides so they don't get damaged if you use the attic for storage or you plan on being up there much at all. Cheap insurance.

You can usually do most of the install yourself and you can get the equipment online but I think I would have a real AC guy do the final connections and charge the system so he can register the warranty. (you can't) Make these arrangements before you buy anything. You might be surprised at his price once you show him what you can buy. Shop around. You should be coming into a slow season for them.

Start by checking out what is available. Do you want to keep the existing heating system and add AC? Do you want to put in a more efficient system with hot air heat and AC? What fuel and power is available?

You may also want to consider a ductless system like the Mitsubishi I know two people that had them installed in the past few years and they love them.

Are there similar houses in the neighborhood? See what they have and how they like it.

Those are very good points, he should look at the whole solution and what he has now, how efficent.

I would take a good look at installing mini or micro split systems instead of a ducted system anless I was switching the heating over to forced air gas at the same time (which "I" would do here because electric is WAY too expensive.

Have you considered making all the ducts 14” (space between rafters) and adjusting the flow with registers with adjustable louvers?