The low bid got the job and that’s why your ductwork system — and I can’t emphasize system — enough, is beyond being balanced. It’s so bad, in fact, that we could not guarantee comfort distribution even if we were to install a full-blown motorized damper system.
"How do you know this?" the unhappy and uncomfortable homeowners asked.
The HVAC installer gave up trying to balance the system and won’t return our calls. So began yet another education process on how the ductwork is a system, the design processes required, and how to determine what needs to be revised. Educating the homeowner(s) establishes trust, and trust trumps price so their sticker shock can be tolerated.
One relatively recent zone damper retrofit came quickly to mind. The owners’ son was a special needs adult who ruled the roost when it came to setting the single zone home’s thermostat. When he was unhappy, there was no peace in the valley. His suite was walled off from the main home with just a single door for accessing his siting/computer room, bedroom, and ADA bathroom with roll-in shower. The parents’ suite was at the opposite end of the single-floor home. The best, most reasonable priced resolution turned out to be adding zone dampers to every run out from the supply trunk line.
The addition of a two-zone control panel and upgraded 120-volt 80-va transformer to handle the full load should all of the motorized dampers be "On" at the same time enables us to install a wireless thermostat in junior’s suite where he could set whatever temperature suited his mood. Don’t ever forget to incorporate a weighted bypass relief damper so the AC coil and/or heat exchanger still has the proper cfm airflow or you’ll be back for a frozen AC coil or prematurely cracked heat exchanger caused by thermal stress overload.
Window units in new homes? That’s how many homeowners resolved their lack of cooling comfort in the second floor bedrooms. The old saying: Unhappy wife equals unhappy life certainly holds true and it was obvious this couple’s nerves were frayed. "Builder calls back in the HVAC contractor who eventually tires of this problem job and says it can’t be fixed."
More than one way to skin a cat!
First things first: Rules of thumb should be ignored because the homeowners are already unhappy and they are frustrated because they paid the builder a huge chunk of money for their dream home that’s not comfortable, and up until now, can’t be fixed. Or can it? Of course it can, but tread carefully because get it wrong and there’ll be more trouble than whacking a hornet’s nest with your fist.
The heat loss/gain calculation provides a rock-solid foundation for the resolution. Do this on a room-by-room basis because the program, I use ACCA’s Manual-J, will tell you the required cfm for each room. Total that to see if the actual installed duct trunk-line can deliver the total cfms required. I use what I always call the Wheel of Fortune, because using it has literally provided a fortune in resolving existing ductwork issues, which enabled us to deliver comfort and it's the ACCA duct calculator (https://www.acca.org/mobile).
Using a duct calculator during the initial duct system design phase also eliminates problems before they can latch onto your installation. I am partial to the plastic manually rotated wheel, but this is available as an app too. Accuracy is the goal we must meet if we are to resolve forensic investigations to determine why comfort was not delivered and what needs to be done to provide the heretofore-elusive comfort.
In many cases, the basic issue is a lack of sufficient return-air from the second floor when the furnace and AC coil is located in the basement here in the northeast. In other areas of the country where basements are not present, the furnace/air handler may be shoehorned into a closet or in the attic when you’re likely to find a rat’s nest of flex-duct.
In the majority of cases, we found the supply side of the ductwork distribution system was adequate and the addition of manual dampers (if none were present) would enable us to balance flow to meet the required cfm per each room. The return duct(s), on the other hand, was substantially undersized for second floors where an open stairwell and/or balcony gave warmed air from the first floor a place to go — adding an extra load to an already undersized upper floor return duct system. Or the returns were located at baseboard level instead of six inches below the ceiling or where there were ho/lo return grills, the lower grill had no damper to close the louvers and air, being lazy, will be favoring a return via the lower grill (down flow system).
Accuracy is the goal we must meet if we are to resolve forensic investigations to determine why comfort was not delivered and what needs to be done to provide the heretofore-elusive comfort.
Three basic choices:
- Install a second furnace and AC system to serve the upper floor only. The addition of a return air filter grill will grab that warmed air rising up from the first floor and we typically installed these in the ceiling by the open stairwell or in the balcony area overlooking the first floor.
- Install a new return air duct sized to grab 80% of the return air required and install it (ideally) on the hallway side of a bedroom or bathroom closet so you don’t end up with ductwork in a hot attic space. If that second floor closet sits on top of a first floor closet, that’s ideal for concealing the return duct. Summer/winter dampers will need to be installed on the two primary return ducts to force the system into pulling 80% of the return air from the second floor.
- Old age problem meets new age resolution. Long, long, ago, minisplits were single-speed units not suitable for stand-alone heating (sunrooms) and best used just for AC. They also did not feature multiple indoor heads connected to a single outdoor condenser. Nonetheless, we often had jobs where this was the best most economical resolution to the uncomfortable temperature imbalance between the first and second floors. "We have to turn the AC thermostat so low, I swear you could hang meat from the ceilings on our first floor in order to be comfortable in the upstairs bedrooms!" The advent of inverter (variable speed) mini-splits changed everything and sales increased substantially year over year. Inverter mini-splits blend seamlessly with existing ducted central systems because they quietly and efficiently provide the amount of cooling (or heating) needed to supplement the shortfall delivered by the defective ductwork design. Sized to deliver the total Btu/h required for both heating and cooling allows the homeowners to benefit from additional energy usage by closing off the ducts to the second floor. The bedrooms now zoned means that as the children grow up and leave home, the mini-splits in those bedrooms can be set way back resulting in less energy spent for those rooms. It’s not uncommon today to find the entire home has converted to inverter mini-splits with the older technology sitting idle or long gone. All of which means, for those of you who embraced inverter mini-splits way back were green before anyone ever knew what being green would come to mean.