Summer Cooling Issues - lots of details inside - help needed

10 years ago

I live in a 2 story townhome with units attached on both sides. It was built in 2007, but I bought it 2.5 years ago. I live in north texas and for the past two summers, the AC just can't keep up. The system only gets down to 78F only at night and only if we aren't cooking. During the day, it struggles to get below 80F. All bedrooms are upstairs.

There are two systems. The system for upstairs is 2 ton. The system for downstairs is 1.5 ton.

Some things that may be helpful to know:

1) Manual J tests indicate both units are undersized by .5 ton each (I need a 2 ton and a 2.5 ton).

2) The condensers are misinstalled. They got switched so that both condensers are operating with the wrong air handlers.

3) Both units have a single return for each. The returns are both upstairs and are apparently undersized. Since both are upstairs, they really support each other. There is no supply vent near the thermostat upstairs.

I've been presented with three different options from three different contractors:

a) Upgrade both units by .5 ton. Add a supply in the hallway at the top of the stairs (same hallway where the upstairs thermostat is - ceilings are tall and hallway is very open). Add a return and supply in the master bedroom (there's only one supply in this large, west facing room).

b) Replace the 2 ton currently running upstairs with a 3 ton and move the 2 ton in place of the 1.5 ton. (In other words, buy one 3 ton system and make better use of the existing 2 ton).

c) Replace only the downstairs system so that there are 2x 2-ton systems. This contractor feels that this is the only way to keep humidity down. He seems to think that bigger upgrades will result in high humidity.

I'm inclined to go with option b plus add a return and two supplies as suggested from option a.

Will this size unit result in high humidity? Will skipping the additional return(1x) and supplies(2x) make for airflow bottlenecks?

This post was edited by elixir75 on Mon, May 13, 13 at 14:43

Comments (9)

SaltiDawg
10 years ago
I'm sure you'll get good sound advice here. I'm just a homeowner, but I have to ask why do you want a supply near the thermostat? Seems that would cause the thermostat to conclude the house was cooler than the representative temperature for the entire space and cause the other rooms to be warmer than desired.

In my two story colonial there is no supply duct in the upstairs hallway where the thermostat is. In fact the upstairs return is within just a few feet of the thermostat.
elixir75
Original Author
10 years ago
The supply near the thermostat was suggested by one of the sales people. It makes sense to me because the rooms always feel cooler than that hall where the thermostat is. The thermostat is at the top of the stairs so it really is probably the warmest part of the house at any time.
Related Professionals
Emeryville Solar Energy Systems · Glen Ellyn Solar Energy Systems · Greenville Solar Energy Systems · Rehoboth Solar Energy Systems · Waltham Solar Energy Systems · Easton Solar Energy Systems · Centennial Home Automation & Home Media · Ferndale Home Automation & Home Media · Franklin Home Automation & Home Media · Scottsdale Home Automation & Home Media · St. Louis Home Automation & Home Media · Surfside Home Automation & Home Media · The Villages Home Automation & Home Media · Fairfield Fireplaces · Farmington Fireplaces
SaltiDawg
10 years ago
Let me understand. Your upstairs is too warm in summer so the solution is to make it seem cooler at the thermostat so that the thermostat will sense that it has done its job of cooling and reduce the A/C in an already too warm house?

Makes absolutely no sense to me. Does it make sense to you? lol
elixir75
Original Author
10 years ago
What I'm saying is that I'd want to add a supply only if it would provide a more accurate reading of temps to the thermostat. I agree the vent shouldn't be too close to the thermostat for the reason you mention. What I'm trying to avoid is having the system running when the rooms are plenty cool, which happens when we close our bedroom door - the cold air accumulates in our room and the temp in the hallway is significantly higher. During winter we have a similar problem with the heat.

There are only 5 total supply vents upstairs (3 bedrooms, 2 baths). With all the warm air coming up the stairway, I'd think there should be at least one supply in that hall.

But I'm not the pro :) What's recommended/customary in this case?

Edit: changed the original post to better describe the suggested supply location.

This post was edited by elixir75 on Mon, May 13, 13 at 14:44
mike_home
10 years ago
Why is the contractor suggesting a 3 ton unit for upstairs, when the Manual J calculation indicated a 2.5 ton load?

Did the contractor who proposed increasing the downstairs to a 2 ton condenser explain how this will solve the problems on the second floor?

I am not getting a good feeling about either of these contractors. Did they present you with written proposals with the details of the equipment and services?

Here are some questions:
What is the area of the first and second floors?
How much insulation is in the attic?
Did you get a copy of the Manual J calculations and can you summarize the results?
Do you currently have a humidity problem during the summer?
elixir75
Original Author
10 years ago
Mike, he's thinking a 3 ton will be an adequate way to compensate for an undersized downstairs system (since both returns are upstairs this sounds logical to me). The summer months are problematic on both floors.

First floor is ~800 sqft. Second floor is ~1200 sqft.

I'll check attic insulation height tonight.

I didn't get a copy of the Manual J. If it's needed to get a right sized system, I'll gladly pay someone to give me a proper report.

I do not have a humidity problem in the summer.

Question: What is the downside of having a system .5 ton larger than needed? I ask because this AC work is getting into pricey territory and I really want to avoid getting a system that doesn't have the headroom to handle entertaining people (extra heat from bodies as well as cooking). Last summer I had the oven running with a house full of people going in/out and it was sweltering inside.
mike_home
10 years ago
The duct work must be large enough to accommodate the AC air flow. Having a larger AC with undersized ducts is not going to work well. If the AC is over sized then it may short cycle. The AC will not run long enough to dehumidify the air.

Did one of the contractors do a real Manual J calculation? They should have least shown you the result. Contractors sometimes claim they have done a calculation when in reality they have not.

I would think the 1.5 ton could handle the first floor. Your problem may not be due to insufficient size. Is the second floor unit in the attic? It may have leakage and poorly insulated duct problems.

I don't understand why there is no return on the first floor. What is the location of the first floor unit?
elixir75
Original Author
10 years ago
Both units are in the attic. There's no leakage according to everyone who's inspected it. Although there's a bad kink in one of the upstairs supply ducts (almost 90 deg) and a minor kink in another.

The option 'a' contractor recommended increasing the return duct sizes and adding a plenum to each return duct grill to increase return air flow (there's none on either).
User
10 years ago
Time to get an estimate from Contractors C & D.