Why is the upstairs a lot hotter in a 2 story duplex?

Question

I've lived in my current duplex for about 5 years now and every summer, my upstairs portion of the duplex gets noticeably hotter than downstairs. I couldn't give an exact measurement but 10 degrees Fahrenheit hotter would not surprise me.

Over the years, I've added several things to the house to deal with this issue. It's made the heat manageable but by no means is it solved. I had to replace the AC (it was 20 yrs old), but even that didn't fix the cooling issue. I've added ceiling fans in all three bedrooms. I've added an attic fan as well to get the hot air out of the attic.

What I'm really doing is just guessing what the problem is. I've looked into companies doing energy audits and insulation, but I'm not sure if this is the most effective thing I can do.

How do I go about solving the hot air in my second floor during the summertime? What is the most effective approach to solving this problem? Is this something I can solve or would it be best to hire a contractor?

Answer 1

Since hot rises, upper stories will tend to be warmer unless the design of your air conditioning system properly compensates for it. An energy audit, as mentioned in the comments by @mikes will tell you if you have any reasons for heat gain that may be correctable.

Assuming you have a single thermostat that controls a unit that supplies both levels, here are some other factors to consider:

• Make sure you have a clean filter. A dirty filter will lower the overall efficiency of the unit.
• Make sure that supply and return ducts are open on the upper floor; it's possible that supply ducts were closed during heating season due to excess heat in that area; return ducts may be blocked by furniture.

• Check for dampers in the ductwork that leads to the upstairs. It's possible that flow to the upper level was restricted to balance the system for heating system. If you change a damper, note the position beforehand, you may wan to return to that setting for heating season (manually operated dampers usually have a small lever on the outside of the duct -- parallel to the airflow is "open", perpendicular is "closed")

• Running the system fan full-time (rather than just when the compressor is running) may help to even out the distribution of cool air.

• If you have rooms downstairs that are too cool, you might close or partially close a small number of supply ducts to improve air flow to the upstairs. Note that you should not close many ducts without consulting with a knowledgeable HVAC person, as you could restrict airflow too much, making the unit run less efficiently.

• If your stairway has a door, leaving it open may help to allow air to circulate more freely between levels (especially if you don't have adequate return ductwork to the upper floor)
• Last, consider having a qualified HVAC specialist evaluate your system to ensure the ductwork is adequate.

Answer 2

Not sure if this would work in your case but I have seen it work really well in a small single level house designed to capture the sun that I stayed a few weeks in over a summer.

Have you tried putting an inlet vent with damper low down in a cool part of the house and a similar vent high up on the 2nd level?

The idea is that in summer if you open up these vents it'll allow the warm air to pass out and as it does it'll draw in the cooler air on the shady side of the house.

No guarantees but you could test this theory out by opening a high window upstairs to let out the hot air and opening a window in the downstairs shady room and ensure that there are no doors closed in between.

The inlet air is critical or else it won't work.

Answer 3

A lot of good suggestions were given, but in my case it ultimately was two things:

1. Poor insulation - the energy audit found the insulation was about 8 to 10 inches too low for our area. Given the age of the house, it wasn't surprising that this needed to be rectified.

2. Soffit vents - or lack thereof. I had no soffit vents to ventilate the attic properly. Baffles were added to prevent the insulation from covering them up. I felt like the soffit vents were a key to our success as well. I thought we had soffit vents, but on closer inspection there were none. From the attic, I could see some light, but from the outside, no vents were present.

Once these two issues were fixed, the upstairs became noticeably balanced and the temperature differential is negligible. I'd say on a bad day, it's 2 to 4 degrees warmer. We have a ceiling fan in the stairway that helps circulate the air as well, but without the insulation it's just not effective.