Correct Size AC

[dbreen]

Inspected an Amana 2005 3.5 ton for a 2300 square foot home this does not seem big enough, the temperature differential was 11 degrees which is too low would this be the problem. Filter and evaporator coil were clear.

[Larry D. Kage]

A lot of variables to consider...

Here is some interesting reading for you:

http://www.nachi.org/forum/showthrea...ghlight=splits

[Jae Williams]

Did you happen to notice the SEER (Seasonal Energy Efficiency Rating)?

The size of the unit can depend on its rating. Three and a-half tons is a lot of cooling.

[Roy D. Cooke, Sr]

Originally Posted by jwilliams4

Did you happen to notice the SEER (Seasonal Energy Efficiency Rating)?

The size of the unit can depend on its rating. Three and a-half tons is a lot of cooling.

WOW! I agree with Jae .
In this case I would just transfer this of to an Expert in ac units.

Recommend further evaluation by qualified AC person.

Roy Cooke sr........ Royshomeinspection.com

[Patrick Bolliger]

General "concept " I read is 1 ton/ per 500 Sq Foot.
BUT don't hold me to that... Depends on so many other factors...

Need the "tempies" (HVAC techs) for a complete understanding...

[Bruce M. Graham, III]

Not sure, but I think around here you have to run a manual J load calc before the HVAC guys can get a permit to do any installations.

[Jae Williams]

Originally Posted by pbolliger

General "concept " I read is 1 ton/ per 500 Sq Foot.
BUT don't hold me to that... Depends on so many other factors...

Need the "tempies" (HVAC techs) for a complete understanding...

Don't count on that...

[Jae Williams]

Originally Posted by pbolliger

General "concept " I read is 1 ton/ per 500 Sq Foot.
BUT don't hold me to that... Depends on so many other factors...

Need the "tempies" (HVAC techs) for a complete understanding...

In another time and another place...maybe. Today, with the higher efficiency units the tonnage is less to accomplish the same thing.

I have a 2400sqft home and when the temp was upper 90's and humid recently for several weeks it was comfortable in our house.

We have a 2.5 to unit--3 years old. There are many factors to consider concerning sizing the unit for a house. (And an 11 degree split isn't one of them...that really doesn't mean a thing for an inspector's purposes.)

[dbreen]

Jae,

Thanks for the information. What do you look for when inspecting the a/c if not the splits. Do you take the panel off and check the evaporator coil etc?

[Michael R. Boyett]

Don, just be aware that there are competing opinions regarding a/c splits and sizing. I too use the very, very rough rule of thumb of 500 sf/ton and I also check for 14° to 21° splits but that's just me. I hear, understand and choose to ignore the temp split nay-sayer's until a better method is presented. Now, have you read the 130 post thread that Larry recommended in post #2 and developed your own opinion? : http://www.nachi.org/forum/showthrea...ghlight=splits

[David A. Andersen]

I'll let Jae answer that, but your job as a HI is to determine if it works, not determine the engineering design.

When you turn on the t-stat, what happens?

NACHI and Sate SOP's allow for extended services, but you had better understand what is going on before you do. It takes longer to become a good HAVC Tech than becoming a Home Inspector. It also requires EPA Certification. If you do all these things, why not work on HAVC? There is more money in it!

We HAVC guys are here generally because we are broken. I broke my back. Some loose their knees! And working for yourself is better than working for an incompetent employer (in my case, one that demanded dry bulb temp splits on all service calls).

There is a lot of good information available here to learn about and there is no dumb question.

Read before you ask though. Then ask specific questions you have. A lot of this info has been covered in the archives.

Do you take the panel off and check the evaporator coil etc?

Our SOP says we do not remove other than user accessible panels. Stick with the SOP. A look at the bottom of the coil through a filter access with a mirror works.

[Mark A. Timpani, CMI]

In az it would be a 5 ton unit.

[David A. Andersen]

I hear, understand and choose to ignore the temp split nay-sayer's until a better method is presented.

A psychrometer and a psychrometric chart is all you need to determine the btu's added/removed from the air.

We need to take enthalpy splits not dry bulb temperature splits.

If we are going to go beyond HI protocol, we need to do it correctly.

[Richard L. Bennett]

I too put my words of wit on the temp split subject. Run the air flow rate down with a dirty filter and the temp split goes high. Run the air flow too high and the split is too low because the air does not stay around long enough to get cooled.

And yes the HVAC boys set these systems up with the math of their butts.

Now where do we sit to say it is good or bad???

Real simple -- does it work at time of inspection?? This is true for hot or cold temp differential. BTU's needed in or out are the same thing if you are too hot or too cold.

To check a system with one reading and say yes or no is going out on a very dead limb. I would rather bet on a current reading from the compressor as to the general health of the unit. Remember a unit could be under or over-sized unit and running as per mfg specs and the client can still be unhappy with the electric bill or some hot or cold pockets in the home that are not at the right temp.

So inspect by the seat of your panes. If you think it is undersized or in need of service go out on a limb and say so. Just be ready to pay the bill if nothing is wrong. Remember it is your opinion

rlb

[Jae Williams]

...an so is presented a better method.

But that sort of thing is not for the HI. We're not there to service the unit.