Got brand new AC ducts and new furnace, but AC temperature split got worse?

[startover909]

Bought (old) 1400sqft house in 2016, replaced AC system with a Bryant 3-ton, single-stage, 16 seer.

Chose not to change AC ducts or furnace at that time. Old ducts in the house = all metal ducts. I understood the old furnace with old blower would also reduce efficiency of my newer AC.

Performance was somewhat decent. I usually set temp at 77F. Measured return air = 76F, supply = 61F, split = 15F.. Only complaint was that bedrooms = always 2F hotter than living room, possibly due to worse insulation in bedrooms or lack of return air (whole house has one single return located in hallway outside the bedrooms).

Decided this year to replace the furnace as well as all the ducts due to mold/bacteria concerns. Today, the HVAC contractor I hired:

1. Replaced all my old metal ducts with R8 flex ducts. They closed one of the ducts from my living room/kitchen area to direct more airflow toward my bedrooms.

2. New plenum, with a UV light installed in it.

3. Replaced old furnace with new Carrier 80% 90000 BTU, single-stage gas furnace (model 58SB0A090E21--20).

After the job is completed, the air flow coming from the vents feels stronger than before. But now return air = 75F, supply = 63F, split = 12F. Temperature in bedrooms is now about 1F (instead of 2F) hotter than living room. Additionally, I noticed that indoor humanity went up from 45% to 48%.

I questioned them before the techs were about to leave and they told me 12F split is normal for the house.

I have not had enough time to judge the cooling efficiency/comfort level/energy costs etc.

But I'm a bit skeptical about the worse split. Is it normal for my situation? I'd expect that after spending $5k+ on the new components, things should work a bit better than before, not worse.

Your advice would be greatly appreciated.

[BaldLoonie]

3 ton is a lot of juice for a 1400 sq ft house. Must be a hot climate? My double thermometer broke but at 420 CFM per ton, I used to run 22° split. So, no, I would not accept 12 for a split.

Looks like a 5 ton blower for a 3 ton air. Knowing the average installer, they left it on high explaining the 12 degree split. Even low may be too much for the 3 ton. Had that happen here. Customer with 3.5 ton air and a very strong furnace that even on low was moving too much air. Humid in there. Have the dealer look at the blower chart, get as close as possible to 1200 CFM. Take a static pressure and use the chart to confirm.

[startover909]

Houston, TX here. House was built in the 1960's, so isolation was poor. The 3-ton never felt quite strong for me in summer time. I previously blamed it on old ducts with possible leaks and non-matched furnance/blower.

So the new stuff should definitely improve it, not make it worse right? If they set the blower too high, that would explain the high air flow but poor split?

[fliks]

Houston, TX here. House was built in the 1960's, so isolation was poor. The 3-ton never felt quite strong for me in summer time. I previously blamed it on old ducts with possible leaks and non-matched furnance/blower.

So the new stuff should definitely improve it, not make it worse right? If they set the blower too high, that would explain the high air flow but poor split?

Yep you are correct and the reason the humidity went up slightly.

[pacnw]

Metal to flex may not have been an upgrade, either.

Flex has more restriction, so hopefully they did a proper calculation to determine correct duct sizing. But I doubt it if their idea was to remove a run in one room to increase it to others and(assuming they did this) did not bother to check air flow for equipment size.

[startover909]

I did hear before that flex ducts are more restrictive than metal. I wanted to change out the old ducts mostly for sanitation (mold etc). The contractor I hired specifically promised that the new duct system they install will give me the same air flow.

Judging from the attitude of their installers and the current situation, I have a suspicion their techs don't really know what they're doing. If they did not properly design/size the system, does that mean I'm potentially left with a much worse performing system? How much work is involved to fix their problems?

Today was a hotter day (90F outside, compared to high 70s on the day of installation) and the split is even worse. Return = 75F. Supply = 65F. Just 10F split. The AC is now obviously struggling to cool down the house.

I want to have a general idea before reaching out to them on Monday for a resolution. Any advice would be greatly appreciated.