Should I even consider an early AC replacement?

[soupcxan]

I have a 2000 sq ft house in Dallas with 11 ft ceilings. Built in the mid 1990s and the outdoor condenser is the original York 4 ton 10 SEER unit. Indoor evaporator coil was replaced in early 2000s and is a Lennox 5 ton. We've been here a couple of years without any AC problems (AC cleaning/checkup at purchase said it was ok) but it has never cooled the house down very quickly. On days when it is +100, even with the AC running the inside temperature can still creep up a degree or two. Air handler and ducts are in the unconditioned attic. I have taken every other action I can to reduce the heat coming into the house, including: radiant barrier foil, blinds, window tint, extra attic insulation, airtight light cans, and larger attic vents. Windows are already double pane. Even with all the changes I made to the attic, it still gets up to 130 in the summer. But I don't know of a good space to move the air handler out of there.

My question is, should I consider upgrading the condenser before it dies a natural death? Or is it a waste to throw it away this soon? I was told when we bought the house that we could buy a new 14 SEER unit that would be compatible with the current evaporator coil. I don't know if this is a good idea or not. Alternately, I can just wait for the condenser to break and then do it. If were going to do an early upgrade, I would wait for the fall/winter (no point in paying summer prices if you don't have to).

I have not called anyone yet to get an estimate because if it's going to cost $ and only save me $100/year on electricity, I don't want to waste their time. I'm paying $0.11/KWH here and using about 11,000 KWH a year, roughly half of that is due to AC usage.

I know that I have not provided much detail, but I would appreciate any thoughts you have or other factors to consider. Is this even worth investigating? I don't know anything about HVAC.

[AvantGarde]

We just put in Gorell double panes and its helped (we live in MS) also have you called a pro to check yours to make sure its running the best it can?

Are you using a restrictive filter?

I'd at least wait through the summer and get something done off season. We got our new 18 SEER Amana HP in early Feb

[bwalley]

If you do a replacement unit, I would replace both the A/H and the condensing unit at the same time, especially since the A/H is 8 years old.

Can you relocate the A/H into conditioned space, perhaps in a closet or the end of a hallway?

Window tint won't do much (no matter what the salesperson will tell you), you would be better off with LOWe double pane windows, but you usually won't get a payback on your windows from an energy savings standpoint.

[glockdoc]

you might consider an attic ventilation fan. they don't use much KW but they move a lot of hot air. be sure to have plenty of soffit vents or it may actually suck air out from the conditioned space. radiant barriers in the attic also are effective.

before you trash your condenser you might have a pro do a heat load calc on your building to see if your unit is undersized. Sounds like it isn't but you never know. Pretty sure cooling load calculations are not sized for 100+ temps here in TX which means most units correctly sized will start falling behind in cooling performance once temps get above approx 97°F

[udarrell]

I am betting there is not enough airflow through the evaporator coil.
It takes a lot of airflow for 4-tons, & humidity shouldn't be a problem Dallas, so I'd be tempted to use at least 425 or even 450-cfm per-ton of cooling, that's 1700 or 1800-cfm.

The ducts could be picking up heat from the attic, or the Return Air may be drawing heat in from the attic!

Click on udarrell & figure out what face-velocity is needed through the diffusers to achieve the required CFM & BTUH for each room. - Darrell