HVAC Question? (Phoenix: new home, heat pump, buying)

[JoeJude]

Ok I'll repost this in HVAC forums, but maybe some locals here will have ideas too:

1950's halcraft house, 4 ton AC unit 1500 sq foot house, my two eastern bedrooms which get a lot of sun are temp measured 5-10 degrees hotter than the rest of the house, that is a lot worse than it sounds when you try to sleep in 80s.

I've put some baby shade trees on the east wall and a trellis, both rooms have blackout curtains and fans, I also literally have rerouted the master bathroom duct with temporary duct work into the master bedroom, so I can't close my master bath door, but honestly it's helping... a little, and noticeably blows better than the registers from the two rooms that heat up.

So today after 3 years of misery I decided to go up in the attic myself, an AC guy had been up there and told me everything was "normal", after going up I suspect he didnt go all the way back. Here's what I noticed:

The very cool rooms in the house, including the master bathroom all have flexible duct work coming off the AC. The bedrooms in question though seem to have solid metal ducting that I suspect has been there since the house was built. I say suspect because that's all I can find, the flex duct clearly doesn't go to the rooms, it seems like solid metal ducting is buried under insulation, I also couldn't say for sure, but some of the insulation felt really cold which made me suspect a leak in the ducts but I couldnt find anything, it's blown insulation which is a pain in the neck when you gotta work in your attic.

What are my cheapest options to fix up my two rooms? Or ughhh.. the best and or most expensive options?

Does this sound like a duct issue or something else?

[Bummer]

First question, JoeJude . . . how old is your A/C?

The reason I ask is I had a 15 plus year old Heat Pump (working ok but seemed to be making more noise and vibration than normal) replaced last June by Chas Roberts.

Not only does the new Heat Pump make a huge improvement in the overall comfort level and greatly reduces the noise and vibration but my Summer Electric Bill has dropped significantly.

Is it possible your A/C is "pooping out" from old age?

[JoeJude]

It's definitely old, at least 15 years, but 1200 sq feet of the house is perfectly cool, including a huge living room that gets the most light. it's the two bedrooms about 300 square feet that are hot.

[Zippyman]

It's actually "normal" to have 10-15% of your cooled air leak out of old ductwork.
Steel ductwork isn't tight unless it's taped or sealed with mastic & that's something that just started being standard practice in the past decade - so it's pretty much guaranteed to be leaking pretty good.

There's really no such thing as "temporary" ductwork, so I'm assuming someone just cobbled in some flex-duct for unknown reasons..

There's really only one correct way to fix that kind of thing - start over with a complete heat-gain / loss survey (manual J + manual D ), then design a new supply (and return) setup. <------- you can't put air into a room without taking air out of a room. Any room without a return-air duct is a compromise (and won't be comfortable)

Many new homes don't even get a "textbook" setup that actually works properly & the odds of finding someone who's willing / able & qualified to do the job properly amongst the hacks & quacks in the Phoenix metro are slim to none, and slim's on vacation.

If you're handy, you can improve things some with a bucket of mastic & a couple rolls of duct tape. (Most "duct tape" actually isn't good enough to use on ductwork btw. You need the stuff with the UL logo on it that actually says "for ductwork"). Every metal joint and seam is leaking & so is every "boot" where the ductwork goes through the drywall. If you can't see the ductwork, you need to dig it up so you can see it. There are no shortcuts in this kind of work. Start with the hot rooms, but understand all those ducts are leaking air (money).

Sealing the ductwork will probably help, but it probably isn't going to be a total fix. Most likely, your "hot" rooms have supply ducts that are too small & also insufficient return-air. In a perfect world, you would add a return to every room, but most older homes rely on the gaps at the bottom of the doors to allow airflow back to a main filter/grill/duct in the hallway (which is also prolly too small).

There are specs out there for the airflow of different sized ductwork, & it isn't even high-school-level math, but I can tell you from experience that the best contractors you're likely to find around here aren't even going to do any math & they'll charge you $500-$600 to just slam an oversized or 2nd supply duct in and call it "good" - it might even work if you're lucky, just understand you're paying for an expensive cobble-job if there isn't any math done first.

If it makes you feel any better, know that just about every house in the valley has an oversized a/c, and an undersized return, so we're all wasting money.

[JoeJude]

Haha entertaining and informative, thanks.

[Ponderosa]

I have some uneven cooling in my house as well. My new AC has a recirc setting on the fan that runs the fan really slow - you can barely tell it is on. If I run it like that the problem is vastly improved. You probably don't have that super low speed setting, but you could try running your fan in the on versus auto position if you have that. Otherwise, I'd look into a window or portable ac for the bedrooms.

[DougStark]

Don't replace your heat pump/AC until it is completely shot. The payback isn't there.

Also, I don't buy the idea of buying expensive, complicated high SEER heat pumps. I bought a basic 13 SEER heat pump- works fine. If I feel extra "cheap", I just turn the evap. cooler on when the dew point is low.

[AZgarden]

If its only you, close the bedroom door, turn up the AC to 85, and put a window unit in the bedroom window. Cuts the bill considerably and keeps it cools at night to sleep.