Replyit could matter. How often does it get 100 degrees in your area? If the system is oversized, it may not de-humidify properly. The important thing is not to size a system based on a few days of higher then normal temperatures.
Regular Guest
I have a 1100 square foot house(excluding the garage).
We currently have a 2.5 ton unit. We are looking to replace our current unit which was installed in 1994 due to not cooling when it's 100 degrees outside.
Contracters are differing on 2.5 and 3. units. Does it really matter?
Professional Member*
it could matter. How often does it get 100 degrees in your area? If the system is oversized, it may not de-humidify properly. The important thing is not to size a system based on a few days of higher then normal temperatures.
Last edited by gregp; 08-09-2011 at 10:51 AM. Reason: can't spell worth crap
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Yes it does.
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I live in Miami, Florida
banned reincarnate
curious, on those 100 degree days, what temp, do you think the unit should get to, that would make you comfortable/happy? and on those 100 degree days what does your current system reach with the 2.5 ton unit?Originally Posted by Mary9921
AOP Committee/Professional Member*
Do the testing to get the data first, on which to base decision on...
Miami, FL, 2.5% summer design 90-F dry bulb, 77-F wet bulb 56% relative humidity.
That figures to be a high 120.69 grs moisture per lb of air.
In that humid climate, a Home Energy Audit should be performed with a blower door test.
After any retrofit work, a manual J ought to be performed.
With that high a humidity, the Infiltration Rate must be kept as low as possible.
The duct system must be examined & airflow tested before selecting a new condenser & matching indoor coil.
From that data, you & your contractor select the best combination of equipment & components that will work best in your climate, with your home, the final duct system & those humidity control needs.
Good Luck...
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udarrell
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Sorry, 3 tons is crazy for 1100 sq ft.
If you really require that much cooling, fix the house and ductwork. Throwing larger equipment at the problem won't make it go away.
Chances are that the ductwork isn't sufficient for the 1000 cfm a 2.5 ton unit needs to move, let alone 1200 cfm for 3 tons.
Global Moderator
The duct system must be examined & airflow tested before selecting a new condenser & matching indoor coil.
There's the answer.Chances are that the ductwork isn't sufficient for the 1000 cfm a 2.5 ton unit needs to move, let alone 1200 cfm for 3 tons.
Professional Member*
As others have stated, make sure your insulation is top notch, infiltration is at a minimum, duct-work is tight.
Then put in a 1.5 or 2 ton, depending on manual J.
Even 2.5 ton, in 100 degree heat, for 1100 sq ft is crazy.
Also as stated here by someone very wise - insulation is something you pay for whether you have it or not.
I have a 1000 sq ft rental, well insulated, with a 32 year old 1.5 ton A/C.
It performed wonderfully when we recently hit 99 degrees. Renter was never uncomfortable.
Keep in mind, a smaller unit will run longer cycles, and therefore de-humidify very well, which is ideal for your climate. On the hottest days, it will run nearly non-stop. That is a good thing.
"Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler
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78 degrees is comfortable
Regular Guest
We are having the electric company come in and perform a test on the ducts before we hire the contractor to install the unit.
the outside model is:Bryant 126BNA03600/inside:FV4CNF003T00
AOP Committee/Professional Member*
That is only ONE piece of the total data needed... listen to what the professionals & others have suggested on your thread...
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udarrell
banned reincarnate
so how low is your existing system bringing the tempature on a 100 degree day!
Regular Guest
approximately 86 degrees
Regular Guest
how cold is the air coming out?
Professional Member *
I live and work down here. And I have seen 3 ton units on 1000 sq. foot that would not cool. Depends on how old the house is. How much outside air infiltration there is. And yes y'all made good points about insulation and all. But most of the older homes down here have no insulation under the floors much less any in the exterior walls. As for duct work sizing, Good luck with that in older homes. Most of them don't have enough space in the attic to crawl in much less fitting the right size duct work in. Roofs down here where never meant to shed snow. Just water. Odds are the original duct work was designed for heat only, The payscale is so low down here most people can barely afford the system muchless new duct work. Another question you should ask is do they ever intend to close in the garage. More than likely they will find that the ductwork is to blame for the lack of cooling plus poorly insulated.
banned reincarnate
good post.I live and work down here. And I have seen 3 ton units on 1000 sq. foot that would not cool. Depends on how old the house is. How much outside air infiltration there is. And yes y'all made good points about insulation and all. But most of the older homes down here have no insulation under the floors much less any in the exterior walls. As for duct work sizing, Good luck with that in older homes. Most of them don't have enough space in the attic to crawl in much less fitting the right size duct work in. Roofs down here where never meant to shed snow. Just water. Odds are the original duct work was designed for heat only, The payscale is so low down here most people can barely afford the system muchless new duct work. Another question you should ask is do they ever intend to close in the garage. More than likely they will find that the ductwork is to blame for the lack of cooling plus poorly insulated.
AOP Committee/Professional Member*
The preceding posts illustrate why it is very important.to have a Home Energy Efficiency Audit with blower door numbers; later with a Manual J heatgain Calc
In FL.; is there any help available from Power Companies or other sources for the preceding work listed above?
Are there any loans that can be paid back with the utility cost savings?
It would important to use vapor barriers & also get the high humidity infiltration down to the minimum 0.35-Air Changes per Hour (ACH).
If you size for long runtimes with the lowest airflow per tonnage for a colder evap-coil for better humidity control higher temps will work okay; they also said they are comfortable at 80-F.
My advice; use large floor type fans to circulate the air & dress to keep cool; that is a much better cost-effective & comfort option than over-sizing an A/C on undersized heating duct systems that won't cool worth a hoot...
Also, try making the Return Air filter area larger.
http://www.udarrell.com/filters_type...lect_from.html
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udarrell
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it's pretty cold coming out of the air vents
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We have pretty good insulation in the ceiling...hubby put it in after hurricane Andrew. And the house was built in 1984. No insulation in the floor or exterior walls
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