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Learning, Sharing, and Teaching => Ask a Mustachian => Topic started by: caleb on April 13, 2019, 03:05:08 PM

Title: Window AC units versus central AC
Post by: caleb on April 13, 2019, 03:05:08 PM
I'm new here, writing with a cooling question for the community.

Last fall my wife and I bought a 1300 sq ft, two story house built in 1898 with old windows and likely lots of small drafts.

The heat is forced air with no evidence of prior central AC, and the floor plan is very chopped up.

We own two window AC units, one of which is about 10 years old, and the other is at least 20.  I do not expect either is very efficient.

In the past, we've used one window AC unit in the kitchen to cool it down when we're cooking, and one in our bedroom to cool it down before going to sleep.  We don't run them constantly, more just to keep it below 80 in the spaces we're using for the maybe 50 days a year that's a concern in our area.

I'm guessing that continuing our old habits with the old hardware is the most efficient setup, both financially and environmentally, but I also don't want to assume that's necessarly the case.

Are there general guidelines for making the window versus central AC choice, or are there ways to at least get a reasonable guesstimate of the better choice given our habits and time horizon?

Title: Re: Window AC units versus central AC
Post by: Papa bear on April 13, 2019, 08:58:54 PM
The biggest issue with getting an old house ready for central air has to do with the air returns. 

Most of these houses had one large return on the first floor that would drop into the basement.  These were gravity systems where the return air was pulled down and the basement air was used to recirculate.

Retrofitting new duct work into an old house can be very expensive.  Iíve done a few, and am contemplating adding central air to a rental.  You could spend a few thousand dollars just on ductwork and then 2-3k to add a condenser and coil to your existing furnace.

For cost effectiveness, keep using what you are using and cool the spaces you use.

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Title: Re: Window AC units versus central AC
Post by: caleb on April 14, 2019, 10:36:02 AM
Thanks for the heads up on the returns.  I hadn't considered that the ductwork might need thousands in upgrades. 

I think that makes a conversion to central AC definitely not seem worth it.  Between the hardware and the install costs, it sounds like several thousand dollars, which several years of total annual electrical costs for us.

In the past when we've had two houses that came with central AC, I also found that we ran the AC a lot more since it was so convenient.

I can't imagine a world where the hardware, install, and greater use costs are all overcome in a reasonable amount of time by gaining efficiency.

Perhaps I'll meter the two window units this summer to see whether they're worth replacing with higher efficiency units, but that seems like the limit of potential savings.
Title: Re: Window AC units versus central AC
Post by: Papa bear on April 14, 2019, 12:15:06 PM
My rental is a side by side built in 1910. I was also looking at adding minisplits as an option.  These would still be in the 1500-3000 range depending on brand and how many air handler heads there are. 

Thereís nothing wrong with window units if you are ok with them.  Iím running into an issue where tenants are now expecting AC, so window units are falling out of favor.  For your own house, itís up to you! 

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