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new homeowner, attempting to fix the upstairs before it gets too hot without getting a second HVAC. Right now, it will be 72 downstairs, but 84 upstairs. We've got a new ecobee thermostat with a sensor upstairs and one downstairs (the thermostat). it attempts to balance the two and has helped some. We had an entire new HVAC and ductwork installed our first week as the existing system died and ducts were full of mold. Looking for any suggestions on how to keep it cooler.

I am about to replace the insulation on the walls as i have attic access to some of them. (current is yellow and damaged from a rodent). After i finish my electrical work i plan on adding a few more inches of blow in. I've also closed about half the dampers downstairs to push more air upstairs.

other than having a second HVAC unit installed dedicated to upstairs is there any other suggestions one can think of? I have a 16 SEER monster unit. 2400 sq foot home, told the unit can cool 3000. upstairs is only 2 bedrooms and a bath- 4 registers. The house originally had attic fans that had live wires going to nothing in the attic i just removed (aluminum wiring...) should i consider adding new fans? This is not my area of expertise, thanks for any suggestions!

not opposed to an upstairs HVAC, but i will be paying off the downstairs one for a bit so adding another is not doable for a while...

  • Why would you be asking before you see the outcome of your insulation improvements? It's not clear what the question is. There are too many variables--current duct layout, sun exposure, climate.... – isherwood Apr 6 '17 at 15:42
  • Is your HVAC unit in the attic or basement? Are your registers in the floor or ceiling, and do you have any ducting in your attic? – mmathis Apr 6 '17 at 15:51
  • HVAC is a single unit (forget what that's called, not a split) and outside. registers are in the floor downstairs, ceiling upstairs, theres a main trunk going through the wall from the crawlspace to the upstairs attic where it branches out and then over the bedrooms. I'm actually not opposed to making the registers pop through the wall instead of the ceiling if it will help. – Ryan Hollingsworth Apr 6 '17 at 15:59
  • @isherwood, asking because i don't feel like more insulation is a magical end-all solution... HVAC guy said a new unit would fix everything so i'm hesitant to believe insulation will be. Although reading suggests leaking ductwork, old hvac, or insulation being the 3 biggest issues. thanks! – Ryan Hollingsworth Apr 6 '17 at 16:01
  • I'm confused. You said "We had an entire new HVAC and ductwork installed...". Why would anyone suggest a new new one? – isherwood Apr 6 '17 at 16:02
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Here are my generic suggestions based on a few decades of home ownership in a climate that routinely ranges from -30F to 100F with dew points approaching 70:

  • Fix up your insulation. Cooling is usually more expensive than heating, and while hot air rises, heat does not. A hot attic with poor insulation means a hot ceiling, which means radiant and conductive heating of your living space.
  • Be sure you have appropriate window treatments. Dark-colored blinds or curtains absorb radiant solar heat and conduct it to your living space's air, as well as re-radiating into the room.
  • Balance your system seasonally. In the summer, your lower-level supply vents should be mostly closed. Your returns will draw air from throughout the home and keep things circulating, and cool air will naturally drop from the upper level. You don't need much (or any) conditioned air feeding to the lower level.
  • Use ceiling and portable fans to augment HVAC airflow and improve human comfort. Moving air evaporates sweat much more effectively.
  • Have reasonable expectations. You may not have been trying to achieve 72 degrees as an indoor temperature, but that's quite cool. 76-78 is much more attainable on very hot days, and generally feels comfortable with adequate airflow.
  • thanks for feedback. I'm doing a lot of your suggestions, as we remodel a room i am installing fans for this purpose. To answer your other Q, 2 HVACs are very common and seem to be the standard here on new homes with 2 floors. we range from 20s-120 in summer. going to work more on balancing the dampers in teh crawlspace, wish i didn't have to go down there spring/winter, but we do what we must. thanks! – Ryan Hollingsworth Apr 6 '17 at 16:29
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    You're welcome. Please be aware that SE is a Q&A network (as opposed to a discussion forum), and "thank you" is shown with upvotes and accepted answers. – isherwood Apr 6 '17 at 16:32
  • +1 for second point, having reflective (or just light coloured) blinds or curtains and using them to keep direct sunlight out can make a surprisingly big difference. – RedGrittyBrick Apr 7 '17 at 8:42
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The following are 2 answers I wrote for other questions. Also, Can you measure the supply and return ducts at the furnace and do you know the actual size in tons of A/C or btu's for the A/C unit. Are there returns in every room or just a single central grill (bad idea). One last thing; if the system is brand new the contractor should have some responsibility to make the system run correctly I would call him back and ask him what he will do to correct the problems.

All the cold air in the house heads to the basement since cold air is heavier than the warm air. In some installations a central return duct and grill is installed in a central location to reduce cost,( this has become the norm) but is only to save costs. Every room should have supply and return registers. you cannot push supply air into a room with out having a way for the air to get out, ( its like a balloon). If you have a central return grill you normally need to have the bottoms of the doors shaved to allow the extra supply air to flow out. If you do not do this then the room will not receive enough air to cool or heat depending on the time of the year.

Home heating and a/c duct systems have changed over the years. The best systems and the most versatile were installed with both high and low returns and supplies. For heating the low registers were used to supply the heat at the floor and the low returns were to take the cold air off the floor. In summer the high supply and returns were used for the same reason, take the hot air off the ceiling and supply the cold air from above. Today it too expensive to install duct systems this way. Today the installation practice is to install high return grills and low or high supply registers. I prefer low supply registers and both high and low return grills; use high returns in the summer and low returns in the winter. Ask an old timer how to do this.

answered Nov 24 '16 at 16:15 d.george

  • +1 for "if the system is brand new the contractor should have some responsibility to make the system run correctly". I would expect them to have configured dampers so that each room is heated/cooled according to its size. – CactusCake Apr 6 '17 at 19:34
  • If the entire A/C system including the duct work is installed correctly there would be only minimal adjustments between summer and winter. In my present home and my previous home the only adjustment needed was to change the returns from low grills open in winter to high grills open in the summer. As other posts said, get the rest of the house in order first then fix the A/C system. – d.george Apr 6 '17 at 22:33

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