We moved into our house about a year ago and the second floor in my house never get enough heat in winter or cold AC in the summer. Our first floor can be a 72F deg while our upstair stays at nearly 66F in winter; while in summer the upstairs stays at 88F while the downstairs is 76F. As per the HVAC guy said, We have a Cadillac of HVAC systems and is more than enough to handle our house.

Our attic is well insulated with bat insulation between studs and about 19 inches of blown insulation plus automatic attic fan, so the insulation is good.

We check the vents and we can feel the air flow through the vents without an issue and make sure there is nothing obstructing the air flow from the vents.

We asked the HVAC guy if having a second zone upstarts will be a solution but he thinks that is not necessary and will be expensive to switch to a dual zone system and instead he recommended playing with the return airflow by closing the 2 returns in the first floor, so that the 2 returns in the second floor will force the hot/cold air to travel upstairs but it doesn't seem to be working.

Any one has any advise on what could be the issue and how to fix it?

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    Returns usually don't have dampers on the grilles, and that would be less effective than adjusting supply vents anyway. Have you tried closing the main floor heat vents partway? That's the usual approach in my area. – isherwood Jan 21 '19 at 22:08
  • @isherwood Yes, I have covered both sets of 1st floor returns with those magnetic flaps but I can't notice any difference upstairs. – Baratier ErebusDuHalm Jan 21 '19 at 22:12
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    Then there's something we're missing. I'd measure the output temperature on both floors. Maybe you're losing heat on the way up. Are any of the ducts on exterior walls or in the attic? – isherwood Jan 21 '19 at 22:14
  • There are no ducts in the attic but all the upstairs vents in every room are on the outside-facing walls. – Baratier ErebusDuHalm Jan 21 '19 at 22:16
  • Unless the ducts travel exterior walls for a significant distance that shouldn't matter much. – isherwood Jan 21 '19 at 22:21

Do you have both a supply and a return in each upstairs room? You need to determine if you have the correct or enough air flow through the furnace. To do so, buy or borrow a thermometer similar to a cooking thermometer that will read temps between about 0 to about 180 degrees and measure the temp rise or fall (heating or A/C)between the furnaces supply and return air. From this you can ascertain the appoximate air flow. I prefer doing it when the A/C is running however it is now January. Also check the temps at the 1st and 2nd registers to see if they are consistent. Post the name of the furnace, the model and the size and the size of the A/C system. If you can, post pictures of the system. More information may be needed.

  • You could add booster fans to duct work. To help or a air handler to move air to make house more even. – user101687 Jun 21 '19 at 22:07

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