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  1. #1

    Guidance for System Replacement

    Hi All - Just looking for some general guidance. Thanks in advance.

    I live in a 2150 sq. ft. 2-story home in the inland part of the SF Bay area (built in 1998). It gets quite warm in the summer (80's-90's) and we use the A/C a lot but hardly use the heater in the winter. I am looking to replace/upgrade the current outdoor A/C unit which is in very bad condition. My whole system is comprised of: York Diamond 80 furnace (P3HUA12L04801B), outdoor York condenser (H2RA036S06A), and an unknown indoor coil unit that sits next to the furnace (can't find any labels on it - looks very generic).

    From what I have read, it sounds like my system is undersized for the size of home and that I should upgrade to a 4 ton condenser with matching indoor coil. And although there does not appear to be anything wrong with the furnace portion of my system, I am thinking that it might be undersized for a 4 ton condenser. Wondering if this is the case and, if so, what might be an appropriate size for the furnace. I have scheduled several visits for quotes next week - just want to be as informed as I can prior to the visits.

    Thank you!

  2. #2
    Join Date
    May 2000
    Indianapolis, IN, USA
    Not sure what you've read but unless you have 0 insulation and a lot of winderz, you probably aren't out of line. There's quite warm and then there's downright hot. We size to 95 but this summer had temps of 105. The average 2150 2 story here would be a 2.5 or a 3 ton A/C. Very rare to find anything bigger in that size house here.

    So, a dealer who just wants a buck will love to put in a 4 ton A/C. And you are right, your furnace is undersized for above 3 tons. But a GOOD dealer will go over everything, do a careful heat gain calc and see just what is going on. Odds are it isn't undersized, more likely under ducted or poorly ducted. Very common complaint everywhere on 2 story homes is insufficient ducting to the 2nd floor so a hot 2nd floor.

    So next week, tell dealers you won't buy without them doing a heat gain calc. If they don't spend the time looking at your home, ducts and registers supply & return, then write them off.

    Where are said supply & return outlets? Floor, sidewall low or high, ceiling?

  3. #3
    Thank you for the response - that helps put things in perspective (we thankfully only hit 100+ on a handful of days). The supply registers are in the ceilings of the 1st and 2nd floors (12 in all) and the return air is in the ceiling of the 2nd floor in a central location (above staircase). It's nice to know that I might be able to keep the furnace and just go with a good quality 3 ton condenser and indoor coil replacement.

  4. #4
    Join Date
    May 2000
    Indianapolis, IN, USA
    With any ductwork in the attic, first suspicion is leaking ducts or attic heat penetrating the ducts and zapping a lot of your cooling. I've seen systems lose over 1/2 of its capacity to attic heat and leaks. So if ducts are up there or furnace too, definitely 1st place to start.

  5. #5
    Join Date
    May 2012
    San Diego, CA
    The perk of living in California is all new units need Title 24 energy calculations... so your hvac contractor should run calcs and size your system accordingly. Do you live in the East Bay? I remember Fremont and San Jose getting to 100 F some days. I am guessing you aren't able to cool your house down during the summer.
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

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