Hi experts,

I've learned so much from this forum (thank you!), and now it's my turn to ask:
The house we moved to, a single-story, 3,400 sq feet, has a single 5-ton unit that seems to struggle in the hot Texas summer.
_____________ Upto 80'F room temperature is to be expected when temp. > 98'F
_____________________ utergreet: ______________

I measured the static pressure before and after the AH:
Return: ~0.38 (new 3M Merv 12 filter)
Supply: ~0.41

This is within the unit's 0.8 Max ESP specs, but
the return is obviously too high and gets me below the 2000 CFM to around 1800.

My question -
Several experts on this forum stated that a single 20x25 filter cannot support a 5-ton unit.

Since this is the current configuration,
what would be the options to remedy the situation?

Thanks!

In general, 1,800 CFM should not significantly ( > 4%) reduce the air handler performance.

Replace ANY & ALL " SHARP RADIUS" duct transition pieces with smooth air flow products.

Use a MERV 8 OR 10 FILTER.

HNY MERV 13 0.31" / 492 FPM Filter Face Velocity
HNY MERV 12 0.___ [ ~ 0.26"]
.HNY MERV 11 0.23
HNY MERV 10 0.17
HNY MERV 8 _0.__ [ ~ 0.15" ]

++++++++
Root cause: 1 system for 3,400 sq feet
________ _ _ _ .:. Duct work is definitely rather lengthy and/or complex.

 

Totally agree with this, but you NEED to add a second return air grill.
I hit this all the time. Your velocity through the grill is so strong that you are also losing filter efficiency.

 

A single 20x25 filter is too small for a 5 ton system.
I suspect you are taking your static pressure readings in the wrong place. Many technicians make similar mistakes.
Additionally, static pressure readings will be incorrect unless the blower wheel is perfectly clean.
3M filters are so restrictive that I NEVER recommend them.

 

How to correctly measure static pressure.
https://www.youtube.com/watch?v=45gX7Jb60JM&t=24s&ab_channel=HomePerformance

 

Thanks for the great responses. Here are some answers/comments:
- There are two large return grills in the house, each connected to a 16" duct. The single filter resides at the bottom of the AH (unit horizontal in the attic). If I were to convert to two filters, what would be the best approach?

- I'll also try a MERV8/10 filter for now and measure the result. I tested without a filter and the return pressure went down to ~0.1
- Agree that the system is too small for the house. Trying to get the most out of it for now...
- I'm measuring correctly before the fan and after the filter (as described in the video)

 

.4” on the supply is very high. A good target is .1”
Look at adding ducts or enlarging the existing ducts.
Is it possible to to install filter grilles and remove the filter at the unit? That would make filter changes easier as well.

 

.4” on the supply is very high. A good target is .1”
Is it possible to install filter grilles and remove the filter at the unit? That would make filter changes easier as well.

The two return grills are mounted to a 12' ceiling and are 18x30 with jump ducts coming from other rooms, so placing filters there would be difficult.

 

An article about proper duct design. Most duct systems are lousy. Many are terrible.
Find a contractor with a Digital True Flow Grid to measure air flow. Or a flow hood, but they’ll have to measure all the registers and add them up for a total.
Many very skilled contractors say they’ve never seen a 5 ton system that had enough air flow. I am inclined to agree.
https://www.energyvanguard.com/blog/my-duct-systems-low-static-mini-split-air-handlers/

 

What is the model number of the indoor unit?

 

It's a Carrier 58STA110