My parents in Miami need a new AC. Their house is split between 2 systems...a 2 ton York for the bedrooms (approx. 800 sq. ft) and a York 2.5 ton compressor/3 ton air handler for the living area/kitchen (approx. 1200 sq. ft.).
The problem is that the living area never cools down below 78 in the heat of the summer and the unit never shuts off during the day. This area includes 3 sliding glass doors and 2 windows that face the west.
The contractors insist on changing the units out with what is already installed since the original contractors already sized it. Well, I disagree, but noone wants to do a Manual J or load calc and only take square footage into account. Man, you should feel the heat coming through these windows in the summer with the shades closed!!
Anyway, should I just tell them to install a matched 3 ton unit even though it might seem like overkill for 1200 sq ft.? Will humidity be a problem? Should I pay some one to perform some kind of heat load calculation? None of the contractors offer that. They just want to install a system and be done with it.
Sorry for the long posting...
Nooooooooo, insist that whoever you are going to engage to perform this work is going to have to break down and perform the necessary load calcs. Otherwise, if they are confident in their 'esp' for sizing, have them indicate to you in writing that you don't have to pay for the system until it has been proven to work properly under design conditions to your satisfaction. You'll probably be getting a load calc. The public such as yourself that insists that these procedures be done, are what is going to force the ones that aren't doing it to get in line. Sorry, but this important step in the sizing process, will best be driven by you, the consumer.
It could be as simple as adding shade to the south & west windows somehow or putting a low E window tint on them. My big slider faces SW. I have film on it and that made a world of difference. Before tinting it, I had a roll down shade outside to keep the sun off it.
The problem with load calculations;
you can easily manipulate the program or the input to make it a half ton smaller or larger ,if not more.So you relly need someone you trust.
Baldies idea is the simplist solution,and makes sense ,because if you go a half ton larger the duct system is most likely too small to handle the extra air flow.So if you go larger,find someone you trust to do the manual D calulations to get the ducts sized correctly.
To find someone that will do it,call and state you want a Maual J load calc. and if it needs a half ton more,you want a Man. D for the ducts.This will save you time and trouble.
800 sg ft @ 2 ton
1200 sg ft @ 2.5 ton
Sized good for normal home with decent insulation and infiltration - even with large windows. I think that you may have other problems that need to be addressed. Existing units may not be operating properly, lack of insulation, etc.
Exterior window covering, tinting, would help.
Also, is living area different temp than other parts of home. Do other rooms get cool while LR is still warm. If so, then ductwork may be a factor.
IMHO - not all good contractors believe in Man. J - but they can still give you good direction on why the problem is occuring with yur present system, and then can recommend solutions.
Keep trying till you get one.
Thanks for the responses. I've considered upgrading the 20 year old windows and sliders for some extra efficiency but that could be pricy. The tinting idea is a good one too and one that I have also considered.
With respect to the AC, the air handler is already rated at 3 tons and the compressor is 2.5. If I just request a 3 ton outside, that shouldn't affect the duct work, right?
I have had 4 contractors come out for estimates and all of them are reluctant to go the extra mile to do the calculations. I guess I just need to keep calling until a salesman comes out that knows what he's talking about.
Thanks again for the responses.`
Yes it will effect the ductwork,unless they sized it larger than needed to start with ,which being in Flordia ,we know this seldom happens.It is usually an oversized system with undersized ducts,ie a 2.5 ton where a 2 ton is needed,the undersized ducts "kill" about .5 ton of cpacity ,so it operates "fine" as far as not being oversized,you pat the electric company a lot extra.