Air conditioning decision

[Moe DeLoughan]

Did any/all of them run a Manual J calc in order to properly size the unit to your needs? Without that, all they're doing is guessing - and guessing can cost you money, since when they guesstimate they tend to oversize to play it safe. If none of them ran a Manual J, go out and get some more bids, and when the salespeople show up, tell them you want to watch them perform the Manual J calc.

I wouldn't assume that those walls can't have additional insulation blown in. There are companies that do that routinely. I had my walls topped off and cellulose insulation blown on top of my fiberglass batts in the attic. It made a world of difference.

Single pane windows with storms can be nearly as energy efficient as modern windows *if* they are in good condition (no cracked glass, putty intact and in good shape, wood frame in good shape, weatherstripping in good shape). So if you had to decide where to budget for energy savings, I'd go with adding more insulation.

[trader_4]

Now we've truly entered the twilight zone. I've seen lots of single family houses in NJ and have not yet seen one with the AC mounted on the roof. And he did say that it's a 90 year old colonial. See many colonials with flat roofs? The idea that if you mount the eqpt on the roof, you could then use the condensate to help cool the roof is totally nuts. First, the condensate doesn't come out of the compressor, it comes out of the evaporator, mounted on the furnace. Are you suggesting the furnace go on the roof? Getting the water to the roof doesn't require mounting the eqpt there, only running a small hose from the furnace there. But then that's just as dumb, because the small amount of condensate isn't going to do anything measurable, significant, nada, in terms of cooling a roof. It;s like a flea farting in the breeze.

Sounds like you've been reading hippie weekly too much.

[trader_4]

I live in NJ and I had 5 companies come out to quote on my system. They ranged from one from HD, a local small company that has been around for 40 years, to a larger regional company with the fancy new trucks. Not one of them did the calculation and I can understand why. If it was your business would you spend the time to do a full Manual J, which is very involved and will take a lot of time, knowing that with most customers you don't wind up winning the deal? I'm not saying that isn't the best way to determine the right solution, only that I don't see how it could work with todays costs of doing business. In my case, I didn't care because I had the performance of the existing eqpt to go by, which IMO is better than a paper calculation.

It seems reasonable to me to quote it with a couple levels of eqpt and then do the manual J when the customer is actually ready to do the deal. The cost diff in the eqpt isn't that much anyway. That's how I would do it and it's kind of how at least some of the companies did it. They never did bring up a Manual J though.

[rangerssuck]

Agreed, especially since one of the companies has done three houses on my b lock (similare age and construction), and the other (which suggested almost exactly the same capacities) has been in business almost 50 years about tw o miles from me and has doubtless done many, many houses similar to mine. T his stuff doesn't come in THAT many different sizes, does it?

[trader_4]

block (similare age and construction), and the other (which suggested almo st exactly the same capacities) has been in business almost 50 years about two miles from me and has doubtless done many, many houses similar to mine. This stuff doesn't come in THAT many different sizes, does it?

Well, actually it does. Furnace could be 40K BTU up to

120K. AC, 1.5 tons up to 5 tons. You do want it right size, erring on the side of larger is obviously better. But like you say, I think guys that have been in business for 20 years, have done many similar houses, go by experience about what size it should be. And they err on the side of larger. They probably do that even if they did a manual J. You put a 60K btu furnace in a house that needs 90K and you may get a call in Jan.

It's just that this Manual J thing is thrown out all the time, but I'll bet almost no contractor does it just to give a quote. It would certainly drive their cost of doing quotes through the roof. While the competitor salesman does X quotes a day, they do 1/3 X.

[Stormin Mormon]

Not sure about NJ, but in NYS, the humidity is usually high enough that a dribble of condensate won't provide much cooling at all. Roof and attic typically have insulation, so even if the water evaporated (unlikely) it will be on the other side of R-## insulation.

[Stormin Mormon]

When Vandy and Al Gore get in touch with their inner person, and give up bathing and laundry, it's a real sixties experience.

[Stormin Mormon]

While it's true that a very under sized furnace or AC will provide poor service, grossly over sized will also be problems. Oversized AC won't remove hudmidity properly, and will leave the cold and clammy feel. Over sized furnace won't run long enough to circulate the air.

When I replaced my own furnace, I had a choice, the 80K came out. I could replace with 70K or

90K, so I went smaller. Glad I did. The floor transition had been a real poor fit, and I tightened that up. The 70K has heated well, even in some really bone numbing cold weather.

[Stormin Mormon]

You might have trimmed some of these 278 lines of text. You didn't need them all. Thank you.

[trader_4]

Not that it really matters, but why wouldn't AC condensate evaporate on a hot roof? Roofs get so hot in full sun you can't hold your hand on them. It's not that it won't evaporate, it's that it's a small amount of water so it's effect on cooling the house is negligible.

[Stormin Mormon]

Summer in western NY tends to be very humid.

[trader_4]

I'd like to see a summer day in NY where it's so humid that condensate water wouldn't evaporate on a hot roof. You have some very strange physics in your universe.

[Stormin Mormon]

There are plenty of days when the attic space AC at my church drain onto the flat roof. The condensate runs off the flat black roof, and drips from the roof to the ground. Nah-noo, Nah-noo.

[Vandy Terre]

Thank you so much for you kind post. Try again when you learn about Jesus.

[rangerssuck]

I'm in Northern NJ, and it's getting pretty hot outside. I currently have n ot enough window units to keep the whole house cool, and I'm thinking it's time to do something.

fered (and all of the pretty similar in price is:

ack yard under the window that now has the big AC, inside unit on living ro om wall. A couple of fans as needed. ~$3500 (minus $500 state rebate)

TU). ~$5500 (no rebate)

0 BTU). $8000

attic, ductwork in 3 upstairs closets, vent in EVERY room first & second fl oor, return in upstairs hall. ~$7500. 1 year parts & labor, 10 years parts warranty.

d any of these (I can), what would be the relative advantages/disadvantages of each? How about the relative cost of operation?

e to Antarctica.

Insulation is not happening for reasons I've stated. It's simply not practi cal, except in the attic.

In my neighborhood, I think about the last thing anyone is worried about is theft of their AC compressor. I can just imagine to look i'd get from the building permit guy if I told him I wanted to mount the unit on my roof. Su ffice it to say that it's simply not happening.

Dribbling condensate on the roof will not provide any meaningful cooling. O f course it will do something, but if I thought for a second that it would do anything significant, I'd collect rainwater and pump it back up to the r oof.

Same goes for "learn how to best vent the existing window system for the mo st comfort." At 100°F and 90% humidity, this is not any sort of ventilati on problem. It's a refrigeration problem.

[trader_4]

. I'm in Northern NJ, and it's getting pretty hot outside. I currently have not enough window units to keep the whole house cool, and I'm thinking it' s time to do something.

offered (and all of the pretty similar in price is:

back yard under the window that now has the big AC, inside unit on living room wall. A couple of fans as needed. ~$3500 (minus $500 state rebate)

BTU). ~$5500 (no rebate)

000 BTU). $8000

n attic, ductwork in 3 upstairs closets, vent in EVERY room first & second floor, return in upstairs hall. ~$7500. 1 year parts & labor, 10 years part s warranty.

ord any of these (I can), what would be the relative advantages/disadvantag es of each? How about the relative cost of operation?

ove to Antarctica.

tical, except in the attic.

is theft of their AC compressor. I can just imagine to look i'd get from th e building permit guy if I told him I wanted to mount the unit on my roof. Suffice it to say that it's simply not happening.

Come on now. You don't see central AC condensers installed on the roofs of colonials when you drive around? You can mount it on a 45 angle, or build a platform. Front side is preferred location. And it makes any servicing so much easier. Plus it's the cool, hippie thing to do.

Of course it will do something, but if I thought for a second that it woul d do anything significant, I'd collect rainwater and pump it back up to the roof.

most comfort." At 100°F and 90% humidity, this is not any sort of ventila tion problem. It's a refrigeration problem.

+1 to all the rest. Even the rainwater solution wouldn't make enough difference in cooling the inside of the house to even begin to justify the expense.

[Vandy Terre]

Sorry for making the suggestion. I must of missed the post explaining why insulation is not practical.

Count yourself fortunate. Theft of AC compressor coils has become a problem in all of Atlanta Georgia.

Historically here in the 'old South' placing old blankets/ quilts over a roof and keeping them wet was a form of keeping a dwelling more comfortable. It is not a great cooling method but it does help some even in the high humidity levels of this area.

Moving air feels cooler than standing air. Opening window tops on upper floors and opening basement or lower floor lower windows helps create air movement. Hey, I am all for AC. Especially now that our highs are in the 90s with near 100% humidity. But I once lived much farther North where knowing how to set the windows could keep a person comfortable until August.

[jamesgang]

block (similare age and construction), and the other (which suggested almo st exactly the same capacities) has been in business almost 50 years about two miles from me and has doubtless done many, many houses similar to mine. This stuff doesn't come in THAT many different sizes, does it?

Typically split systems start at 1.5 tons and go up in .5 ton increments to 3 tones and then in one ton increments from there. Occasionally you might see .5 ton increments further up than 3.