HVAC vs. Window Units

[jneblett]

I have recently purchased a home built in 1963 with no A/C. The original owners for the past 43 years have lived with window units. In richmond it gets hot and humid in the summers. I cant decided to bite the bullet and install central air or cool the house with window units. The price quotes I have gotten have been much more than I ever anticipated. Should I try it for and year with the window units or go ahead and install the central air? Any insight or help is appreciated

[gevans]

Things to consider:
Central air (c/a) is typically far more energy efficient than window shakers.
c/a will increase the value of your home
c/a will increase your comfort level.
c/a will increase the resale value.
c/a will make the house easier to sell.
c/a is harder to steal than window units.
Window units provide easy access to your house for a thief.
c/a looks better, and
You still have the use of your windows.

The only things going for window units:
cost
you can cool only parts of the house, saving energy
cheaper to replace when they fail

BTW, I vote for central air.

[propmanage]

How many widow umits would you need?

[pstu]

I am a homeowner in S.Texas, also hot and humid. Lived 22 years in a 1955 house, think I can guess the style of your 1963 one sans AC. A central air system with all its ductwork is a hassle to take care of (I've got two in my house). I plan to go whole hog and install a two stage AC within the year, but it's not clear you would want to follow in those footsteps.

Are the window units doing the cooling job for you? The dehumidification job? Have you considered keeping window units for less used rooms, and installing a "Mini Split" system or two to take care of your most used rooms? The mini-split could get pretty good efficiency, and would avoid ductwork and all the pitfalls that go with ducts. The main drawback that I know of, is mini-splits are good at cooling one room only.

A central AC system is an unfortunately complex system. If you install one, you will want to get a heat load analysis done to identify cooling needs room by room -- that is best done by the "Manual J" procedure published by ACCA (Air Conditioning Contractors Association). That is already something 90% of the AC techs I meet, don't want to do. It's also something you can DIY using the software sold on this site. It's great software, I have licensed it twice, your main work is measuring room dimensions, and choosing insulation, windows, etc. from a list they give you. It's also enough work you may prefer to pay $XXX for a pro to do it for you. Many pros will promise to do it once you contract them to do the whole job, in those situations it normally is no extra charge.

Then they properly should run through ACCA Manual S and identify the actual AC equipment which will meet your cooling loads. It is simpler than Manual J or Manual D. It is my cautious opinion that many pros might get by with seat of the pants experience instead of Manual S, however I think skipping Manual J would be a danger sign.

The next challenge for central air is duct design, ACCA method is Manual D. Another case where techs often don't do it, I think one reason is the math involved bugs some people. But if the duct system is not done well, there is no way your central AC can deliver comfort to all rooms. I would at least seek a tech who is comfortable talking about "external static pressure" and semi-promises a design with 0.5 or less (maybe higher, many existing houses run 0.7-0.8. The units are "Inches of Water" on a manometer). Again, I predict 90% of the techs you meet will not want to do that. Including the lowest price bidders, almost certainly. You can perhaps see why faced with all these challenges, plain old window units don't look such a bad alternative.

Seems to me the mini-split approach gets you most of the benefit for a room, while avoiding many of these pitfalls. Allows you more latitude for *you* to make choices by seat of the pants experience, which is good.

It is very true that central AC and heat will enhance the resale value of your home (hard to sell one without it in Texas). And true that window units take away your view, and can be more easily stolen.

You can verify lots of these challenges by perusing this board, however you have 1 post so far and probably haven't had the time to do a lot of reading. Sounds like you live the simple life, you may want to go slow in complicating it. Of course it's awkward discussing going without central AC on a board where most people make their living from it. But many pros can help with mini-split systems too, all I know of them comes from reading this board.

Best of luck -- Pstu

[Edited by pstu on 12-05-2006 at 01:28 PM]

[klabkebash]

I have a one bedroom APT and have 3 window units. And im in the HVAC business. If I was allowed to, I'd install a central AC for sure.

After 1 year, the units get nosiey, they cool only that one area. and you can see the lights in the place dim whenever the compressor kicks on, i always have to be warry of blowing fuses if I have too many applicances running at once.

[jneblett]

Originally posted by propmanage
How many widow umits would you need?
4 or 5 units would probably work the house is 2800sq/ft

[coordinatesales]

You've been given some good advice here already so I won't add much. I speak to people almost daily who are in your situation. If you can afford it, go with central ac/heat done by a contractor who MUST use manuals J and M in designing a proper system for you. You will be more comfortable, the system will be quieter, more reliable and efficent. Mini-splits have their applications as well but putting equipment in every room brings their price close to a central system with ductwork. If you can live with putting them in main rooms that may be the way to go. They are also very quiet and efficient. Chances are, the window units currently in there were purchased for a lot of reasons other than proper sizing so they may or may not cool or control humidity properly.

[jneblett]

Fantastic. Thank so much for all your advise

[cem-bsee]

that said, it depends upon your desires & $$ -- & your envelope & shading --

I can cool my 2133sf with two 5000btu "shakers" -- by letting the ID temp drift to 82F when Outside is >95F -- 1 in kit, 1 in office -- BUT I live in the middle of old woods= lots of shade -- 140+ trees on 0.74a lot.

[dan sw fl]

Originally posted by jneblett

Originally posted by propmanage
How many widow umits would you need?
4 or 5 units would probably work the house is 2800sq/ft Also, 4 zone mini-splits are available.

What's your budget? I am sure
I can Use it All !

[barak]

IVE ALWAYS UNTIL NOW INCLINED WITH CENTRAL but after a few swminars-ive got to admit there are major drawbacks with central-heat must have humidifer-if not maintained-w-can cause humidifier fever disease/if filters are nit changed reguraly-can cause allergy and sick building syndrom i do not lined ducts for insulation or ductboard-its illegal in ca and i personally think its hazadorous down the road/new houses must have makeup air do to tight constuction-sick building syndrome is very comon/unit must be sized right and duct designed right/must have enough combustion air and vented properly/if done by a person very knowledgable ok/ but the healthiest heat is radiant and baseboard/central is quiet/and nicer but window units can be worked without doing the whole house/window units are noisy and messy and are pieces of garbage the way they are made today/if you are on a very tight budget i think you can hold off/if you do central get a few opinions with someone with alot of experience

[gcook]

Mitsubishi makes ductless many split systems that can have up to 8 zones. This system is very quiet and adds the comfort and energy efficiency of zoning.

The ductless systems are amazingly quiet and do a great job since they use variable speed indoor console units that can better control humidity and temperature.

If you have time check out the S-Serie unit from Mitsubishi.

[heykiss]

Sizing central air with manual-J is the way to go if you close up the house for the hot months and leave the t'stat at say, 74 deg. The problem is when you go to work and set up the t'stat to 80 and return from work at 3 o'clock with a occupied start at 1 o'clock and 74 deg.setpoint, but the space temp. stays at 77 deg. until 5 p.m. It's a great starting point, but sometimes engineering numbers are not my final sizing number. Dehumidification requirements, tree shade, type of outdoor environment, etc. add to the sizing of a system. In the end, there's always one or two days a year where even the best planned system isn't perfect. Central air is best because you can sleep at night and you're not moving heavy units twice a year.