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I'm getting a couple bids for this and have been told I fall between the 1.5 and 2.0 ton for the requirements. The 1,100 sq. ft. home is fifty years old but has new windows, doors, duct sealing, attic insulation, solar attic fan and foam insulation in all of the outdoor walls.
I set my AC for 78 in the summer but we have many 100 degree days. I also have shade from 3 different trees.
I've been given the option so far for a one speed 1.5 ton units or a two stage 2.0 ton, though no estimates have been finalized. One contractor who mentioned it said variable speed models might be the best choice, but they are too new and may need to have the bugs worked out. He also said there are many more choices at the 2.0 ton level than at the 1.5. Suggestions?
I plan to be in the house a while so am looking for long term ROI.
So I'm guessing if I hadn't done the upgrades I would be needing a half ton more?
The only way you'll know for sure is to have a HVAC company do a Manual-J calc.(by someone who actually knows how to do it- not the typical walk-in, "oh, its about X-number of sq/ft, 3-returns, 5-registers, OK; good to go!!!"). If all the "upgrades" are up to or better than the standard for your region you maynot need any more than 1-1/2ton.
From your description, I'd say a 2ton would probably short cycle.
The only way you'll know for sure is to have a HVAC company do a Manual-J calc.(by someone who actually knows how to do it- not the typical walk-in, "oh, its about X-number of sq/ft, 3-returns, 5-registers, OK; good to go!!!"). If all the "upgrades" are up to or better than the standard for your region you maynot need any more than 1-1/2ton.
From your description, I'd say a 2ton would probably short cycle.
I've been told that Manual J is mostly for new homes and that it doesn't reflect old construction methods/materials very well without tweaks. Not true?
I've been told that Manual J is mostly for new homes and that it doesn't reflect old construction methods/materials very well without tweaks. Not true?
Not true.
A Manual-D (ductwork) is improbable because if the ductwork is existing- it's existing. Not much you can do there. But determining the load on a house can be done and since you know whats existing and been added, it shouldn't be a stab-in-the-dark.
Just FYI- most new construction requires a Manual J, D, and S for permitting purposes today.
If ROI is the key you're looking at window A/C, not central. You need just shy of 18,000 btus for the houses about 50 years old in the Austin area. Providing the plan has good air flow properties one unit located to take advantage of the flow can cool and heat the home. You can get one for under $600.00. You could even use smaller units that can be shut off during the day when a room is not normally used like an extra bedroom or kids room. FWIW, my A/C installer built a house west of San Antonio without central heat and air. He uses window units claiming replacement costs, maintenance, and utility bill is far cheaper than central. I'm skeptical at best but it does make sense not to A/C or heat an area if you aren't using it. He claims the window units today are just as reliable and energy efficient as any central unit on the market. There are many out there that heat and cool. My brothers house in the country is a concrete block, 2200 sq ft home that he cools and heats with one window unit. The unit cycles off and on just like a central unit. You can turn it down to well past uncomfortable on a hot day that you'll be looking for a coat. The back of the house does run about 5 degrees warmer than the front though during the summer heat. It does just fine during the winter with more than adequate heating. Something to consider.
I agree with Trapper, beyond what he says, consider that if your central air goes out, you are 100% without air, but if you have several window units, unlikely more than one on the fritz at a time.
That and central heat/air is over-rated, IMHO - do you really use your whole house all the time? Overnight do you really need A/C other than in the bedroom?
I have not heard of this AC unit approach as I always thought it was a compromise. So the coil and compressor are in one unit? Do they have SEER or EER ratings for them?
Actually I thought the latest and greatest for homes not set up for central was the new ductless, e.g. Mitsubishi.
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