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Thread: Generator Size

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  1. #1
    Join Date
    Jul 2011

    Default Generator Size

    I want to purchase a generator to run 2 sump pumps in my house. I am choosing between two sizes:

    Smaller: 3500w continuous / 4000w starting

    Larger: 5500w continuous / 6875 starting

    If you look on most generator sizing guides, they say that a sump pump pulls about 800w when running, and about 2000w when starting. Even running both sump pumps at the same time (that would be 1600w), the 3500w generator shouldn't break a sweat. Starting one while the other is running (800w + 2000w = 2800w) should also be OK.

    But you never know when sump pumps are going to turn on, so my concern is what will happen if both sump pumps try to start at the exact same time? Both generators have overload protection, so would that stop the generator from breaking? Also, how long would a sump pull that starting wattage. If it pulls 2000w for a second or two, then it's possible that both sump pumps could overlap when they try to start. If it's only for a fraction of a second, then it would be less likely for them to start at the same time (since that overlap window would be smaller). Also, if it happened, I wonder if one sump pump is starting, and the other would try to pull the wattage that isn't available, will it just strain for a second and then start a second later?

    My concern isn't the cost difference between the two generators...it is the gas usage. In NJ, this past week, getting gas during the outage has been a nightmare. The 5500w generator listed above runs (at 50% load) for 10 hours on 7 gallons of gas. The 3500w generator runs (at 50% load) for 12 hours on 4 gallons. That means that the 3500w generator consumes gas at about half the rate, which is a big deal when gas availability is sparse.

    Since I really don't need to run anything other than these sump pumps, I'd rather go with the more gas efficient model if possible. Thanks for any comments that you have!
    Last edited by ed3120; 11-04-2012 at 03:33 PM.

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