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Installing Central Air in My Old House


I have a raised ranch built in 1978 with radiant heat, hot water base board heaters and a whole house fan. I'm looking to upgrade my house w/ Central Air. Is this even possible w/o ripping the house up? How/What/Where do I start? My friend told me I need a new furnace to go along w/ the central air, but I'm content w/ the heating system I currently have. Is this really necessary?

Any advice, tips, or information is appreciated.



Re: Installing Central Air in My Old House

IS this a single story ranch, or a 1 story? Size? Where are you located? First and foremost it needs to be sized correctly. Properly sized equipment can operate up to 30% more efficient than oversized equipment. More than 50% of AC systems in the US are estimated to be oversized. I cut my cooling bill upstairs by over 60% by downsizing and installing efficient 2 stage equipment.

Find a contractor which will do a load calculation and will do proper ductwork sizing. This is 100x more important than what brand, and needs ot be factored into pricing. If they use a "guess" based off experience, you have a 50/50 shot at best if it's sized and installed correctly.

IF it's single story, you can put the air handler in the attic but make sure the ductwork is well insulated and sealed. Then you just cut the correct size and number of registers in the ceiling of each room. Depending on heating fuel costs, (electric vs. gas) you can also put in a heat pump for mild weather (above 35-40F) that will use less energy and not overheat the space like a boiler can.

2nd option is a ductless minisplit system with multiple indoor units. One in each room.

Re: Installing Central Air in My Old House

If you are on a slab, then putting an air handler and ducts in the attic will be the least intrusive. If you have a conventional foundation, you might see if any of the local contractors have an all-in-one outdoor system. The whole thing sits outdoors, the trunk goes through the foundation wall and then ducts radiate out from the trunk to each room.

Both of these system will have cycling losses so it is important not to oversize the unit as mentioned above. The attic system would probably be the best as cold air tends to fall. The all-in-one would probably be the cheapest installed. The mini splits mentioned are a little more intrusive visually and audibly, but would have the least cycling losses, if any.

Most new central air units are sold with a heater. The all-in-ones are available with a propane/natural gas heater or heat pump. Mine is propane and these are very popular in my area. I have seen them installed on homes with a slab, but the trunk then has to run up a side wall and into the attic. That is not pretty, but I suppose you could cover it with a fake chimney.

Re: Installing Central Air in My Old House

No need to rip up everything, I think the suggestions offered should be great and worst case if you have to run a trunk in a corner or along a ceiling, it can be framed with drywall to cover it. A furnace unit is not a required addon so yes you can keep your existing hydronic as the method of heating. I actually heard this is better than forced air anyway.

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