ac size

[Jon Clark]

Greetings,

I am badly in need of opinions. Although I have seen this issue discussed in several threads, I still am uncertain as to which direction to head.

I recently replaced our AC. At the time of the quoting process, my house was calced at 31/2 ton (1800sf, ss, 100+ summers). Upon selecting the contractor, I asked for the 16 seer. I was told it only came in 4 ton, but since it was 2 stage, it would not be oversized for my house. I went with it. 2 weeks after install, I was on the manufactures web site and saw that the unit was not 2 stage. I presented this to the rep and he got back to me admitting he had made a mistake and that brand did not have a 4 ton 2 stage. Although, he claims they will make it right, he feels that the 4 ton single stage will be OK for our house/area (of course). So far we have not had enough hot weather to heavily test the unit. We have had a few warm days where we ran it for a few hours. I did notice it being slightly humid, as far as what constitutes a short run cycle, I am uncertain. It didn't seem to start/stop excessively.

So, should I press for a change out now, wait for hotter weather before deciding, or is the difference between 3.5-4 ton so marginal that there is likely no problem? Thanks in advance for any advice.

[udarrell]

Concerning the condenser, it is unthinkable that he could have made such an error in claiming he was installing a two stage unit! I need to know what major city you live near to get the Summer Design Conditions there! Here in SW WI with Heat Indexes up to 104, there are 2400-sq.ft. homes with 2-ton units cooling them perfectly. You need a manual J (heatload sizing) done, also manual D (duct sizing), & then a manual S (unit Sizing) done, even then both tend to oversize to some degree.

At the top Click On: Basic AC Overview - "Specifications vs. Reality" - udarrell

[Jon Clark]

At the top Click On: Basic AC Overview - "Specifications vs. Reality" -

Thanks for the response. I live near Sacramento CA though we are typically

3-5 degrees warmer. I had 3 different calcs down showing 3.5 ton, but of course that doesn't mean any of them were correct. I am leaning towards having them put a 3.5 ton in, but I was hoping that someone would show reason as to why it would be pointless. Do you know if he was full of crap in his opinion that a 2 stage 4 ton would indeed be a good fit? He basically explianed that most of the time the AC would be running at a 2 ton level except for the middle of the summer where the 4 ton would be needed. Thanks.

[udarrell]

udarrell

Sacramento, CA Summer Design 98-F dry bulb 70-F wet bulb around only

25% Relative Humidity. Even if it is 3-5 degrees hotter with that low a humidity the system should bring the sensible temp down with ease unless you have extreme heatload conditions. We cannot do a manual J from here, however the experts claim the manual J and S tend to oversize the systems. I know nothing about your system ductwork, airflow, etc. Therefore, I'm simply whistling dixie.

I use a mere half ton 6,000-BTUH room AC that cools perfectly the first floor 3 rooms & a hallway, over 900-sq.ft. at 104 Heat Indexes!

900 / .5 ton = 1800 Sq.Ft per a ton of cooling in an old 1930's home, come here on our hottest days and I will prove it to you! (Airflow!) (It's True.)

Below is an outstanding PDF "Basic AC Overview - Specifications vs Reality" by John Proctor, P.E., Proctor Engineering Group, LTD:

HVAC TECH PERFORMANCE RATINGS "AC Specs vs Reality" PDF - Few are done Right!

DISCLAIMER: I assume NO responsibility for the USE of any information I post on any of my Web pages or in any NGs. All HVAC/R work should always be done by a licensed Contractor & properly licensed Techs! This information is only placed on these pages for your understanding & communication with contractors & techs. This information is also for the edification of Contractors and Techs. I am NOT liable for anyone's screw-ups! - udarrell

[udarrell]

udarrell

Sacramento, CA Summer Design 98-F dry bulb 70-F wet bulb around only

25% Relative Humidity, 75-F indoors at 50%-RH.

Even if it is 3-5 degrees hotter with that low a humidity the system should bring the sensible temp down with ease unless you have extreme heatload conditions.

We cannot do a manual J from here, however the experts claim the manual J and S tend to oversize the systems.

I know nothing about your system ductwork, airflow, etc. Therefore, I'm simply whistling dixie.

I use a mere half ton 6,000-BTUH room AC that cools perfectly the first floor 3 rooms & a hallway, 900-sq.ft. at 104 Heat Indexes! Even if we reduced it to 800-sq.ft. it would be 800 / .5 = 1600-sq.ft per ton of cooling. At 900-sq.ft. / .5 ton = 1800 Sq.Ft per a ton of cooling in an old 1930's home. It says "cools rooms up to 225-sq.ft., not with my techniques; it cools over 7 times that area with NO other AC running anywhere in my home.

Come here on our hottest days and I will prove it to you! My brother knows it is true, but we both can't believe it, it is unreal. (Air Circulation & putting an optimal heatload on the evaporator coil!)

(It's True.)

Below is an outstanding PDF "Basic AC Overview - Specifications vs Reality" by John Proctor, P.E., Proctor Engineering Group, LTD:

HVAC TECH PERFORMANCE RATINGS "AC Specs vs Reality" PDF - Few are done Right!

A majority of ACs are oversized. When a system does not cool sufficiently it is 'usually' due to other factors other than unit sizing!

DISCLAIMER: I assume NO responsibility for the USE of any information I post on any of my Web pages or in any NGs. All HVAC/R work should always be done by a licensed Contractor & properly licensed Techs! This information is only placed on these pages for your understanding & communication with contractors & techs. This information is also for the edification of Contractors and Techs. I am NOT liable for anyone's screw-ups! - udarrell

[Noon-Air]

That depends on what part of Sacramento....Is it in the middle of down town?? or is it by the river??

Maybe somebody should tell ASHRE??

yup

[Tony]

I am not HVAC perso but "Darrell" you know that you are full of crap with 104 heat index and 2400-sq ft.he be lucky to get way with 4 ton Tony say that

At the top Click On: Basic AC Overview - "Specifications vs. Reality" -

[Bill]

It's ASHRAE, ACCA publishes the Manual J. What do you use noonie?

[Jeffery Lebowski]

Wow, nobody woulda guessed...

You f*****ad--I run a 5 ton w/ 7500 sf home here and it works fine...

[CJT]

sound like Tony full of it

[Tony]

well you have you opinion and I have mine

[Noon-Air]

Come on down here...currently 93 degrees, 76 degree dew point and 105 degree heat index..... and its not even summer yet.

[Tony]

You better realize that in dry area is require slightly larger AC unit why because of skin effect, have you ever hear that word before if you want know why my hourly rate is $100, PO will do fine thank you Tony

[Jeffrey Lebowski]

Please explain how in the world would it even be possible for you to have an opinion on the above.

Look, that 104 gives us about 30 degF from comfort zone...though wet most the year during this kinda weather its typically dry as hell.

Wintertime different shit altogether.

--Still using heat pumps but now we be talking what 50~60 deg differential from OA.

IOW...NOW is when to add more tonnage.....

[Anonymous]

LOL jeff lebowski is a hack and a dumbass...not worthy of anyones consideration!

HAHA

-Canadian Cool

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[Zephyr]

Well just out of curiosity I took an existing project [using ACCA Manual J Software] and it showed that if [using my structure details] I changed the "wet bulb" temperature only leaving all other factor's... this is what I found:

@75º F w.b. = 8.01 tons [Normal for most areas] @68º F w.b. = 7.05 tons [Normal for areas coastal areas within 30 miles of the ocean] @50º F w.b. = 5.62 tons [not normal most area's but dryer than most - just to expand the exercise.]

Draw what you think.

[Bill]

I'll wait till Tony explains it some more.

[<kjpro]

Yeah, like his statement (I mean BULLSHIT) below...

"I use a mere half ton 6,000-BTUH room AC that cools perfectly the first floor 3 rooms & a hallway, over 900-sq.ft. at 104 Heat Indexes!

900 / .5 ton = 1800 Sq.Ft per a ton of cooling in an old 1930&#39;s home, come here on our hottest days and I will prove it to you! (Airflow!)"

[udarrell]

"You are correct kjpro," on reassessing there are a lot of walls and a kitchen cupboard area,. therefore I am reducing the actual area to

700-sq ft., that would be 1400-sq. ft. per ton in a 1937 home with a lot of windows. That is over twice what most of us would consider the BTUH per sq. ft., ought to handle the heatload. Eight foot ceilings or 5600-cu.ft of air to remove the latent & sensible heat from. It has a cool basement below the first floor and a hot second floor area above it, which I usually cool toward evening only one room, the hallway & bathroom using a 20" floor fan to circulate the air. I use a 12" fan directing air into the Return Air of the 5,950-BTUH Kenmore Room AC. It cools things down in a short time span to a low comfort level.

It is not easy for me or my brother who lives within 75 yards of me to believe it either, however, I have been used two different a half ton room ACs for many years have been doing precisely that, as stated here & on my web page. I do not expect you or anyone else to believe it, because if I were not experiencing it I would probably tell someone else that it would be BS, too.

I really like this 6,000-BTUH 9.7-EER Remote controlled Quiet Partner Series Whirlpool that I have been using for the past three years. It has three speeds and excellent airflow through the evaporator coil. If the humidity is high I operate the fan a lot on the low speed.

I was using only one 20" fan at the AC, I just bought another 20" Wind Machine 3300 to put in the kitchen to circulate the air faster back to the Room AC. Yes, it says it cools rooms up to 225-sq.ft., it is the positioning of the fans and the long to continuous runtime that make the difference.

Thank you kjpro for your input, the needed adjustment should be closer to the reality! I am always open to corrections!

- udarrell

[HVAC fella]

&#39;I recently replaced our AC. At the time of the quoting process, my house was calced at 31/2 ton (1800sf, ss, 100+ summers).&#39;

REPLY: If you are in a locale that sees 100 plus temps. often, I would not hesitate about putting in a 4 ton capacity system. The difference between 3.5 and 4.0 tons is very minor (6,000 btus). In addition to a 4 ton system, make sure you have a roof mounted Attic Fan with adequate intake air. THis combo will work well.