Cooling upstairs bedrooms

[smokey0066]

I've got a central ac unit in the basement (unfinished) that is setup for 2 zones, main floor and upstairs. Its always been a struggle to get even cooling upstairs. Some bedrooms get really cold while others (west side) have a tough time cooling down in the evening for bed time. I've tried adjusting the dampers in each room but it doesn't help much. AC/Furnace is ~20yrs old and sadly the second floor ducting is run in the unconditioned attic so I know I'm fighting a losing battle. I'm finally fed up with it and I asked an HVAC guy to come look at it. I'm trying to be prepared to ask the right questions when he comes so I get value out of his time while he is here. On the phone I asked them about ductless mini splits and they said they can definitely quote something when they come out but they said maybe all I need is a booster fan.

I've got a lot of questions running through my head.
Do you think a booster fan would be sufficient? I have no experience with these and I'm concerned we're just throwing parts at it.
If I go with a mini split I'd like to put one in each (4) bedrooms so everyone can independently control their temp. I assume this will be the most expensive option.
Should I consider re-ducting in the conditioned envelope to increase cooling performance? Not excited about tearing into the walls/ceiling to do this.
Am I on the last legs with my 20yr old system?

 

[toolmiser]

Not an expert, but my hvac person was really concerned about having enough cold air returns, and if you have some that would collect from the ceiling, all the better. I've made a bunch of mine switchable so I can draw from the ceiling in the summer, and floor in the winter.

 

[fitter30]

Two stories need their own system for cooling. Heating doesn't pose that big of problem. Small cooling only air handler with a return in the hallway with a filter grill with flex duct to rooms ceiling grills. Could also use a mini with a ducted air handler.
Look at a youtube cleaning a mini wall unit.

 

[dcg9381]

The "dual zone" systems can be a pain in the *** with the damper. I think you're doing it right initially by talking to an HVAC guy and seeing if he can adjust the air flow through a use of restrictors or other modifications. Has this home ever cooled correctly upstairs?

I love ductless units, but adding 4 new AC systems, associated compressors, electrical, and all that probably isn't ideal. Maybe there is a a 1/2 way point if you could do one unit and route the original ducting elsewhere?

 

[cad70]

Our 2 story with unfinished basement has a manual restrictor/damper in the main duct that goes upstairs. I open the flow to upstairs in the summer, and restrict it in the winter.

 

[Firebrick43]

Is the ducting that is ram thru an uninsulated space insulated itself?

If ducting and returns are properly sized right there should be no need a separate system upstairs. I have lived in two story houses and been in multiple others that have no issue whatever maintaining even temps room to room.

My guess without looking is that you have a return issue on the warm rooms.

 

[brewchief]

At 20 years old your current system is approaching the end of it's service life, it's possible it could go another 10 years or it could have a major component fail very soon.

Ductwork in the unconditioned space isn't great but isn't the end of the world if it's sealed and insulated properly. What type of duct work is it? Metal with insulation wrap? Flex duct? Fiberglass ductboard?
Sometimes simply replacing old flex with r-4.2 insulation with new flex with a much higher r value and making sure there's no air leakage can make a considerable difference. Oftentimes replacing it with a size or two larger on the hard to heat or cool rooms will help out as well.

Make sure those rooms have proper attic insulation as well, I can't tell you how many times a customer would swear a house is really well insulated and we'd open the attic and see r-13 or r-19 batts and nothing else.

 

[G-ManBart]

There are mini-splits made for multiple zones, so that's what I would look at first. Each bedroom would have their own air handler and controls.

We added a mini-split to the loft in our house and it made a huge difference in the overall cooling of the house, and a reasonable improvement in the electric bill in the Summer. The loft is off a great room with 22ft tall ceilings and it was simply not possible to push enough cold air up that high when it got really hot out. Now the cold air goes across the loft and falls down into the great room so the main central AC only runs when it gets really hot.

 

[danski0224]

I've got a central ac unit in the basement (unfinished) that is setup for 2 zones

As in 2 thermostats?

, main floor and upstairs. Its always been a struggle to get even cooling upstairs. Some bedrooms get really cold while others (west side) have a tough time cooling down in the evening for bed time. I've tried adjusting the dampers in each room but it doesn't help much. AC/Furnace is ~20yrs old and sadly the second floor ducting is run in the unconditioned attic so I know I'm fighting a losing battle.

Absolute worst place for ductwork.

I'm finally fed up with it and I asked an HVAC guy to come look at it. I'm trying to be prepared to ask the right questions when he comes so I get value out of his time while he is here. On the phone I asked them about ductless mini splits and they said they can definitely quote something when they come out but they said maybe all I need is a booster fan.

I've got a lot of questions running through my head.
Do you think a booster fan would be sufficient? I have no experience with these and I'm concerned we're just throwing parts at it.

Probably not.

If I go with a mini split I'd like to put one in each (4) bedrooms so everyone can independently control their temp. I assume this will be the most expensive option.

You also need refrigerant linesets and condensate drains and power.

Should I consider re-ducting in the conditioned envelope to increase cooling performance? Not excited about tearing into the walls/ceiling to do this.

Make the attic conditioned space by spray foaming it. This could be the lowest total cost option. Especially when attic ductwork is not accessible without cutting the ceiling up.

Am I on the last legs with my 20yr old system?

No one can answer that question accurately.

There is a lot to doing ductwork properly. Poor fitting choices at the air moving equipment will kill performance. Some well placed changes near the fan can make dramatic improvements to system performance. There are cool pictures in the back of ACCA "Manual D" that show effective lengths of duct fittings.

Sheet metal ductwork that is not sealed during installation is guaranteed to leak a minimum of 20%, and that is if it is installed well. Poorly cut out holes for runout taps will make leakage worse.

Your duct leakage can be tested- it is called a duct leakage to outdoors test. I have seen 30% leakage rates. Several thousand dollars of equipment is needed to do the test.

Any way you slice it, fixing it properly will not be inexpensive.

I would not pay for duct sealing without before and after testing- especially of an attic system. Be warned that duct sealing can create additional problems- like revealing that there is no longer enough return with the duct holes plugged up.

First order of business would be a load calculation for each room, and verify duct sizing. Then measure delivered airflow and returns. Only then can a repair path be figured out. If you want it done right.

Or, just go buy some window units.

 

[KansasArt]

I ran into the same problem. This was a single zone unit trying to push cool air to the 2nd story. Uninsulated duct work carrying the air probably 70-80 feet from the basement to the 2nd floor. Would have to set the thermostat to 60* so it would run almost continuously to keep the 2nd floor in the 80’s when it got really hot. Our solution was to have a heat pump installed in the attic. It’s only job is to condition the air for 4 bedrooms. To save a few bucks I ran the wiring and made all the cut outs in the ceilings for the registers and one big one in the hallway for the return. About 10 grand ten years ago. Works great with one caveat. When it gets cold it can’t produce enough warm air. Even with the built in heat strips. It only required 10ga wire so I’m guessing higher current heat strips can’t be added without installing a smaller ga wire. The only other issue is I still have to remind the other occupants to keep their doors open when ever possible since the air return is in the hall. Would do it again.

 

[gungatim]

I heat and cool three floors. In the summer, the basement and first floor vents get closed and only the upstairs stay open. I reverse the process in the winter. It's not perfect, but a ceiling fan on low in the bedroom helps move the cool air.

The only thing I wish was I had put in a 2nd thermostat upstairs so I could use that one for the on/off cycle instead of the first floor.