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Why Is My Upstairs Hotter Than My Downstairs?

My high school physics teacher, Mr. Ploplys, said you can’t fight physics.  Hot air is always rising and cold air is always falling.  If you live in a townhome, you know first-hand how this gets worse as you walk to the upper floors.  The laws of physics apply, but we can at least help!  


One way to win the fight for comfort in your home is air movement.  Set your thermostat fan setting from “auto” to “on” to constantly mix up and redistribute that hot and cold air.  Properly sized and multi-stage or modulating air conditioners will help with this as well (see below). 

Hot Roofs and Attics  


Temperatures in poorly ventilated and poorly insulated attics can easily reach 140 degrees F or more making a sauna seem breezy.  Ensure your attic is well ventilated and insulated or that heat will make your top floor uncomfortable. 

Leaky Ducts 

Unfortunately, I can almost guarantee your duct system is at least a little leaky.  In fact, it’s not uncommon for duct systems to have 25% leakage or more!  This porous ductwork is very bad news for your wallet and comfort.  Leaks on the return side draw in sweltering, humid, and unfiltered air making your A/C work harder, burning through more of your utility dollars, and wearing out your equipment faster (not to mention adversely affecting your air quality).  Leaks on the supply side squirt out conditioned air you just paid to cool down – just like leaving a window open with the A/C on.  This means less cold air is making it upstairs where it is needed most. 

The solution for leaky ductwork is easier than you may think and doesn’t involve busting open walls nor rolls of duct tape (which actually isn’t even meant for ductwork!).  Aeroseal is a fantastic leaky duct solution.  Check out this video from This Old House and if you don’t have 10 mins to spare, skip to about 6:00 minutes in.

Uninsulated Ducts 

If your ductwork is not insulated, or worse yet, runs through a scorching attic, the air may come out on the second floor several degrees warmer than the first floor.  Moreover, this air has a longer and often more tortuous path to get from the basement up to the 2nd floor.  Air is lazy so more of it will come out on the 1st floor rather than winding it’s way all the way up to the 2nd floor.  

Solving this is a bit trickier.  Can you get more ductwork up to the 2nd floor?  Can you better insulate that ductwork?  Does your system have sufficient ductwork to allow balancing (slightly closing off dampers supplying cooler rooms to allow more airflow to warmer rooms)?

First Things First


Check off these boxes before you do anything drastic:

  • Is your filter clean?
  • Switch to a low resistance filter that isn’t reducing airflow to the 2nd floor.  If you filter has pleats (looks like a white piece of paper folded back and forth), it probably isn’t helping.  Go with an inexpensive fiberglass filter.  For high quality air filtration that doesn’t reduce airflow, check out 
  • Get your A/C system cleaned and tuned-up for tip top performance by an HVAC professional. 
  • Check 2nd floor registers – are they being blocked by furniture, books, clothes etc.?  Are the dampers open?  Are they delivering good airflow?
  • Try closing blinds and shades on hot, sunny days – especially on windows facing south and west. 
  • Replace older light bulbs that give off a lot of heat with LED bulbs which are much cooler.

Other Solutions

High Return – Hot air will “stack up” on the upper floors of the home (our townhome friends know that better than anyone).  If you have a return duct that can draw that hot air from the highest point and bring it back to the a/c system to be cooled, it will dramatically improve comfort of those upper floors.

Multi-Stage or Modulating A/C Systems – Most older A/C units have one “speed” – full blast!  Imagine your car’s A/C only having 2 settings – Max and Off.  Sounds uncomfortable doesn’t it?  Well, that’s the extent of the capabilities of most home A/C systems.  They come on full speed, blasting A/C into the 1st floor which cooling before the second-floor ductwork has cooled off.  This is just like the people in the front seat of the car getting cold and while people in the back are still hot.  Cooling the house down rapidly also causes the system to shut off before it has run long enough to dehumidify the home. 

Multi-Stage and Modulating units are becoming very popular because they provide better comfort, just like your car’s A/C system.  They will run at a low “speed” providing consistent cool air and they run longer which delivers multiple benefits that owners love.  Longer run times mean more mixing of the air in the home fighting the hot air rising/cold air falling physics problem.  Longer run times also significantly improve comfort from much better dehumidification.  Furthermore, much the same way highway cruise control mileage has a higher MPG and delivers less wear and tear on your car than stop and go, longer run times at a lower speed save you money on utility bills and reduce wear and tear from too frequent starts and stops. 


Zoning – If your ductwork is set up to allow for it, an HVAC professional can install a zoning system consisting of separate thermostats and motorized dampers that will only send air to floors or areas of the home that need it.  You can set the different areas of the home to separate temperatures and really dial in your comfort.  While this is a great solution, it doesn’t work for all duct systems and oftentimes requires multi-speed A/C units and compatible furnaces.


Separate Systems – Sometimes running the fan in “on” mode, sealing the ductwork, upgrading the system, and improving the attic/roof insulation just isn’t enough.  If the duct system was designed or installed poorly, there’s no remedy other than a supplemental A/C system for that top floor.  If your attic has space for a conventional system, great!  If attic space is tight, consider a high-velocity system such as Unico or Space Pak.  If those don’t work, ductless split systems are fantastic solutions to provide quiet and efficient air conditioning.  These work great for 1 or 2 rooms or even an entire floor.  

Contact Shavitz Heating and Air Conditioning for your Chicagoland HVAC service needs!

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