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In a side-split on three levels, four including the basement, the heating and cooling unit is almost new (2 years), and the heating/cooling unit was only available at 35% more cubic feet capacity than the house. Hence it should be quite easy for it to handle the volume of air inside.

Both summer and winter I keep the air ciculation turning on perpetually, whether the heating and cooling unit is on or off.

The thermostat is on the main level, set to about 68F/20C in the winter and a little more, 70F/21C, in the summer.

Despite all these factors, each year in May and September I find it necessary to move my desk, in May downstairs and in September back upstairs. Otherwise the temperature is too uncomfortable for an extended sit-at-the-desk session. I found it easiest to just buy a second desk, and move everything else (monitor, monitor arm, laptop, paraphernalia, desk chair).

Is this:

  1. Normal or near-normal. Regardless of the roof and wall insulation, the rooms upstairs will have to heat up if the house (detached) is baked throughout the day from the sun. In the summer the temperature outside is regularly 80F/28C and sunny.
  2. Not normal. The description above indicates that the walls and especially the attic are not sufficiently insulated.

The bedrooms are upstairs, but the extra heat is not an issue, because the temperature outside is anyway cooler at night.

In this question I'm not even seeking a solution yet (there is already a huge leafy tree on the east side and another, even larger, on the west side). I'm first trying to understand what is to be reasonably expected for comfort inside at all levels.

Quantifying (following isherwood's comment):

I'm asking for a round-the-year issue, but mentioning specific temperatures may help. In this late May, and while the temperature outside is a pleasant 65F/19C, I haven't even switched on the A/C unit yet. Despite that, the upper southwest room (used as winter office) reached 78F/25.5C yesterday. The air circulation is on. Is this heat level normal? Could a room that's baked on two sides for the whole afternoon be expected to remain cooler? (Notice that it became much warmer than the outside.)

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    @isherwood You're right. Does the update give a better picture?
    – Sam
    May 22, 2020 at 14:59
  • It's a start. The behavior you describe is attributable to solar gain. You therefore need to tell us about your siding and windows and any trees involved. The answer you've accepted is wildly speculative.
    – isherwood
    May 22, 2020 at 16:27
  • You're using it as a home office. Does the temperature increase similarly on weekends, when you're not in the office? What if you're working at night? Do you close the door when you're working? The temp increase could be from the electronics and your own body heat. Turning on the room lights, my laptop, 2 monitors, and sitting down to work will raise my office 8-10 degrees in 3 hrs, day or night. May 24, 2020 at 17:26

3 Answers 3

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This is quite unreasonable for a newly installed system with plenty of capacity.

You may want to check:

  • Duct work.

    • Ensure that everything is attached properly. We've had ducts disconnect in our crawl space. (It was after many years, but it's still worth checking for you.)
    • If you can't get to the attic/crawl space to physically examine the duct, ensure you're getting even airflow out of each supply vent in each room. You can use an IR thermometer to check the air temperature coming out of each duct to see how much difference there is in outlet temp. (These can be picked up for around $20 or less at your favorite "cheap imported tools store". They're handy for other things and just fun to have around, so it's money well spent.)

    • Ensure that flexible ducts haven't been crushed. (I just discovered a supply line in hour house was crushed between the strapping holding it up and the large cold air return that was in the same strapping.)

  • Insulation

    • Did you have the same issue before you replaced the HVAC systems?
    • Buy, rent or borrow an infrared camera (or pay someone to look for you) and look at the outside of the house on a hot day looking for cold spots where air is leaking out. (The same works on a cold day looking for hot spots, so this will work whether summer or winter is coming in your hemisphere.)
  • Windows

    • We just replaced all our single-pane windows with new double-pane windows last fall and the temperature difference in the whole house was fairly substantial.
    • If you have double-pane windows but they're older, they may be leaking air somewhere around the framing.
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  • Your suggestion of inspecting the ducts is very interesting. It didn't seem that the folks who do home inspection even look for that, but then they know a little about everything, and not a lot about any one particular specialty.
    – Sam
    May 22, 2020 at 15:00
  • Silly question: you use the infrared camera inside the house, not outside; is that right?
    – Sam
    May 22, 2020 at 15:00
  • I think it could work from inside or outside, @Sam. However, from inside, if the system is blowing air you're going to see hot/cold spots near the outlets that will throw off your readings. I'd think from the outside is better, but I'm not an expert. You may want to ask a whole new question about using an IR camera to check for air leaks. (Note an update to the "duct work inspection" section, too)
    – FreeMan
    May 22, 2020 at 15:13
  • From outside would be fine. There should be a temperature difference of at least 10 deg Celsius between inside and outside. And it should be done at night time with no daylight involved after all exterior surfaces are cooled down from direct sunshine. In other words, best time is before sun rise.
    – xeeka
    May 22, 2020 at 15:20
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I have seen what in my opinion are crappy jobs on multi floor systems. No single system at the same static level year round will ever heat / cool properly. I install adjustable dampers in the trunk lines both supply and output for the air handler. In the summer the upper floors are wide open and the lower floors closed down ~20% this pushes more cold air up where it is warmer. In the winter I reverse for the lower floors to be open and the upper floors throttled back. This uses a limited amount of natural convection or heat rising cool falling because of the density.

It may be possible to add trunk dampers this is the best and easiest way to adjust for summer winter temp changes , even a very well insulated home should have dampers in my opinion not only in the rooms and each room to be balanced but on the trunk lines to the different levels so the house comfort is similar on all levels.

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In top of the other answers, Ill add some anecdotal experience in temperature management from the perspective of a desert dweller.

In this newly-ish built home (2016, but relatively new building standards for California homes) even with insulated ductwork, keeping the HVAC fan circulating without the cooling unit running will eventually circulate warm air from the attic space air warming the ducts. Effectively allowing outside hot air to heat the inside air by thermally radiating through the ductwork insulation.

And in my desk-spaces case, the room has 3 outside walls, one that is west facing therefore in direct afternoon sunlight, and a covered entryway that traps hot air and heat-soaks the walls and walkway. So, surrounded by hot air on 3 sides. Outer wall insulation should keep the thermal exchange under control, but in running network drops I found the insulation on the entryway wall lacking. On top if all that, the roof line is quite shallow over the hot exposed half of the room putting less blown in insulation between the hot roof underside and the ceiling of the room, and then there is the wooden structure directly heat-soaking with little to no length between the roof gables and ceiling rafters. All of this culminates in a room that will track outside air temps within about 5 to 8 degrees in the summer without mediation.

One thing I have done that does help when the AC is running is used a length of dryer vent tubing and a pair of old PC fans to vent the heat directly from the top of the room out of the side non-sun-facing window. Mounted one end about 8" from the ceiling in the corner with a 80mm fan in it as an intake fan(modified with a speed control knob to combat outside wind loading on the outlet fan), and the other tube end taped to an 80mm to 120mm adaptor with a 120mm fan that sits perfectly in the frame of a slide up window. Add a few old Xbox game cases and thick doubled over towel to seal off the remaining open section of window, a few shirts on hangers hanging on the blinds to prevent the frame/glass on the west wall window from driving a convection flow behind the blinds, and now the room drops down to 67F every AC cycle while only hitting about 74F between cycles on 90+F days. It can get almost uncomfortably cold if its a long cycle. Working in boxers helps too, if your home situation allows it. Keep in mind though this will be venting inside air to the outside, which will have to be replaced so overall AC efficiency will take a non-zero negative hit since its essentially introducing warmer outside air into the living space through normal air leaks somewhere in the structure.

Also, remember, hot air raises. So upstairs will always be warmer than downstairs (Id personally set up in the basement, but I'm a polar bear. The colder the better. Its easier to layer for warmth than it is to cool off). HVACs do their best to their design and implementation, but we're still slaves to the laws of physics. One possibility if youre interested with home automation is motorized dampers and distributed thermostats allowing the HVAC system to direct treated air to specific areas as opposed to circulating the entire house when just a few rooms need a burst of cool/warm air. Of course commercial motorized dampers are a bit pricey, but if you're handy you can fit steppers/servos to cheaper 'dumb' units, possibly using low cost ESP wireless serial units to a controller. But if you're not up for a week or two of fiddling, might be best to just get one or two smart damper units to just cut off larger less needed rooms and focus cooling in the more occupied living spaces.

Definitely listen to the HVAC pros in other answers. Im just some jerk on the internet sharing my experiences dealing with the effects living under our doom star. But hopefully this offers some food for thought in managing room heat. Side note: my deak space has 3 monitors (two of reasonable efficiency and one we refer to as 'the heater'), a laptop on a 6 fan cooling pad, and a PC with a 120W CPU (though its usually peaks at 60W or so under normal usage), and 3 fans (celing, stand up, and desktop) so a fair thermal load for a 12'x12' room. But keep in mind fans dont cool, they just move air. Evaporative effects of air moving over the skin cools(to a point). Every fan motor is putting heat into the room. So if you also have a number of fans the net effect will be a warmer room. However, with all of those things trying to slow roast me, the ceiling vent trick still keeps the room almost uncomfortably cold when the AC kicks on.

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