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What would you put on emergency backup generator?

orange_cat | Posted in General Questions on

If you wanted to outlast a winter/summer storm that knocks the power out in an all electric house (heated/cooled with a Air to air heat pump, plus resistance-based hot water radiant heat) and a woodstove – what would you put on a backup panel?

The idea is to have a small propane/dual fuel roll-out generator. Assume 2-3 days no power.

Or a summer storm (so need AC).

Refrigerator and stove are the obvious ones.
Some lights.
Sump pump (?) 
What else? (I do not think hot water is in the cards, but just circulating the cold water should be feasible?)

I forgot to think about it and now the electrician wants to finalize the electric panel and I could really use help. 

I would not be doing laundry (or running a dishwasher or ironing or any other energy demanding tasks) but I would like to be reasonably comfortable (and I have kids).

Obviously I can get a whole house generator, but I do not want to store too much propane/fuel. No gas line. What is the optimal point where the performance is adequate and the fuel demand is something manageable?

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  1. gusfhb | | #1

    We stream everything so that is a must
    If you are sizing for AC, that is probably a pretty big unit.
    anything 240 volt is going to pull current
    I have a well pump that needs an 8kw generator to start[not sure why but it does]
    Without AC I can truly run the whole house , and we don't use the oven. Dryer is gas

  2. Eric_U | | #2

    We're looking at amps rather than watts. Due to price not being that bad, I'm grabbing the 200amp Champion standby generator that runs on propane. Figured it wasn't worth saving $800 or whatever to have to pick and choose half the house. We are all electric too and I would suggest looking at the power consumption of anything heat related. You mentioned a stove which can add up fast. The stove we are getting have five burners and if all were on high heat, would be using something like 9000W at 40a. Obviously you most likely won't be cooking a full Thanksgiving meal during a power outage, just just something to think about.

    If I was on a really tight budget and had to use an existing ~4.5kW 30/50a generator, I guess I would choose to just not have any major appliance other than refrigerator and water pump (if you're on a well). Then just lights and ceiling fans. If it is hot open a window or sit under a fan, if you need to cook then use a charcoal grill. You need to be able to see and flush toilets though.

    1. gusfhb | | #3

      48kw generator? that be a big generator.
      Feeding that will cost a pretty penny.

    2. Expert Member
      BILL WICHERS | | #5

      >"We're looking at amps rather than watts. "

      No, you're "looking at watts" with a generator, because that's how generators are rated. Just to keep things simple, watts = amps * volts. Voltage is 120v or 240v, depending on the load. You work out generator capacity and loads IN WATTS. You work out circuit capactity IN AMPS. They're not really interchangeable, even though they are related.


  3. Expert Member
    Akos | | #4

    I would find out if your utility allows for this:

    This backs up the whole house and you can choose which devices to run.

    Otherwise, sump pump definitely goes on the genny, power goes out during big storms which is when you need it the most.

  4. Expert Member
    BILL WICHERS | | #6

    If your concern is "storing too much fuel", there is something else you need to consider: propane tanks need to be sufficiently large so as to be able to "boil off" enough propane vapor to support the demands of the generator. A typical BBQ tank isn't going to be able to do that, and many also have a flow restricter that can also cause problems when running a generator.

    For generator use that you expect to last for a few days, you really want a permanently installed propane tank, probably 100+ gallons. You need to size it to be able to boil off enough vapor to support the generator you plan to use and it needs to be able to do that at the coldest time of the year when you expect to need the system to work. The colder it is outside, the lower the vapor delivery capacity of any size tank. Keep that in mind, as it's very important and often overlooked.

    My preference would be a whole-house transfer switch, then just be careful what you turn on and off. You always seem to want "one more thing" to be on generator otherwise during an outage. If you're stuck with a subpanel, I would get your telecom stuff (Internet, etc.) on there, sump pump FOR SURE, water well pump FOR SURE, fridge/freezer, some strategic lights (stairs, near wherever the generator is, near the electric panel, etc.), and a few outlets in the open where they're easy to reach to plug in the things you forgot about when you put the system in. The "strategic lights" should be able to illuminate anything you might need to work on during an outage, which always includes the area where the generator is, the electric panel, and often a garage light, basement light, light or two in the kitchen, all the places you might need to fix something or where you'll be during the outage. If you plan this out when you build your home, it's easy to put all those strategic lights on one circuit.

    Coincidentally, my first meeting today is in regards to a 150kw generator I'm installing for a customer's building :-)


  5. walta100 | | #7

    Is the lack of AC a threat to someone’s life? Maybe I don’t know but for most people it is not.

    How often is your grid down? The numbers say the grid is up 99.9% of the time so on average it will be down 8 hours a year.

    How many tens of thousands of dollars will it cost to buy a generator large enough to run your AC? It does not stop their generators this large require preventive maintenance contract that will cost money every year. Your generator will have an exercise program one day each month the generator will start its self and run the house for half an hour or so and make a bunch of noise and slowly drain you fuel tank so you can’t count on having a full tank when you do have an outage.

    I do own a medium sized portable generator. Inevitably moments after I get the generator started the power magically get restored.


  6. Expert Member


    I agree with Akos and Bill. Either a whole house transfer switch, or put a lot more things on the back-up panel than just essentials. You don't have to use everything that's on the panel when the power is out, but that gives you the choice as to which circuits get turned on. It also future proofs the set-up if you get a larger generator later on.

  7. orange_cat | | #9

    Thank you very much -whole house transfer switch seems perfect.

    1. Expert Member
      BILL WICHERS | | #10

      If you're looking to save some money, you may want to look into an "interlock kit" for your main panel, which is the cheapest way to go (but far from the best). If you want a much nicer system, I'd go with an ATS (Automatic Transfer Switch), which is the most expensive option, but also the best. Note that with a portable generator, the benefits of an ATS are reduced, but the ATS still gives you the ability to easily upgrade to a fully automatic system in the future if you want to.

      Either way you go, I recommend you install an "inlet" on the outside of the house where you plan to use the generator when it's running. An "inlet" is like a receptacle but in reverse, and it's permanently wired back to the transfer switch. You use a simple extension-cord like cable to connect the generator to the power inlet when you need to run the system. This type of arrangement makes the system easy to use, and also safer and more reliable.


      1. orange_cat | | #11

        Wonderful, thank you

      2. Expert Member
        MALCOLM TAYLOR | | #12


        So no suicide cord like I use? :)

        1. gusfhb | | #13

          Damn light weights. Where is the fun if no risk is involved.

          1. Expert Member
            MALCOLM TAYLOR | | #14


            A stormy night where you can hear but not see the trees going down in the dark around the house. You were going to take the generator in for a carb kit during the summer but forgot. Who wouldn't want to add a suicide cord to that scenario?

          2. gusfhb | | #15

            Exactly, nothing like a little 240 v across the chest with wet hands to let you know you are alive, or, err, were alive a minute ago............

        2. Expert Member
          BILL WICHERS | | #16

          No! Never! Those things are named they way they are for good reason!

          Go get yourself an inlet and an interlock kit and do things right, so that you can keep posting here after the next storm :D


          1. AC200 | | #18

            I know people that did that during Super Storm Sandy. Suicide cord into dryer outlet. I won't even do that for supplying power from a conditioner to a wall mounted TV. Always install the inlet plug.

          2. Expert Member
            MALCOLM TAYLOR | | #20


            Jokes aside, I switched my exterior outlet for an inlet a few years ago for about ten bucks. It is connected to a red coloured outlet on the interior of the wall, so the whole set up is identifiable as being for the generator.

  8. AC200 | | #17

    Going through this process right now. Hit water table during foundation dig, so keeping sump pumps running is a must. Sump pumps, furnace fan, fridge/freezer and direct vent water heater and internet are the priorities. AC is a nice to have but not essential. Rather let my neighbors plug their sump pumps in. Seems wasteful to cool down a house with a back-up generator.

    The price difference between a 14, 18 and 22 KW generator is very small. I sized the requirements at 10 or 14 KW based on no AC, but they run specials on the 22KW all the time so it's almost the same.

    It looks like like I will probably end up with a 22KW one just based on how they sell them.

    1. Expert Member
      BILL WICHERS | | #19

      I recommend the battery backed sump pumps too. Wayne makes a very nice battery backed sump pump, much better the more common Basement Watchdog systems that you usually see, but any of those is better than nothing at all. An added bonus to having a battery backed secondary sump pump is that it will also act as a backup in case of your primary sump pump failing, buying you some time to replace that primary sump pump. There are more reasons for backup sump pumps than just protection from power outages if your pump runs a lot. I have a fully automatic permanent generator here, and a battery backed sump pump too. Very nice to know the sump pump is pretty much guaranteed to work when needed. I also have the two pumps plumbed with seperate drain lines, to make sure a blockage of one drain line won't keep the pumps from working.

      BTW, from those wattage numbers, you're probably thinking Generac generators. I've not had good luck with those. You see them all over because they make it very easy to become a dealer, but that doesn't make them the best in terms of reliability. I like the Kohler units much more. If you really need reliability though, you want an 1,800 RPM liquid cooled unit (i.e. with a radiator like your car), which will far outlast any of the 3,600 RPM residential standby systems. The 1,800 RPM units are commercial units though, and will be significantly more expensive.


      1. AC200 | | #21

        I've used Wayne battery back-ups before. The flimsy plastic things do work when needed. My big issue is remembering to maintain and change the battery. I replaced it with a Liberty Water Jet back up pump, but not sure that was a great idea to use city water to run a sump pump.

        The current design is two sumps, two pumps, each on its own circuit and then back up generator. I also have a Liberty portable transfer pump I can connect a garden hose to if all else fails and I still have power from the back up generator. Actually I have a hand pump and 5 gallon buckets as a real last resort. Can you tell I'm paranoid about sump overflow?

        I'm looking at both Generac and Kohler. Kohler is about 20% more, size for size.

        1. Expert Member
          BILL WICHERS | | #22

          I don't blame you being extra careful with sump pumps! I'm not a huge fan of the water powered backup pumps. Those things do work, but they are horribly inefficient (i.e. they waste a LOT of water), and they seem to break a lot. They also don't help you in the case of a really big power outage, since the city pumping stations usually go down then too and you have no water pressure as a result.

          The Kohler units are far, far better quality than the Generac units. I usually see them pretty close in price too, but I get dealer pricing for both so that might be why. The Kohler units have a much better engine in them, and are much better in terms of life expectency and also extended periods of run time (i.e. multi-day outages, especially when it's hot outside). I know someone who maintains off-grid systems as a buisness who won't use anything else for that reason. There are also a lot of reports of Generac units catching on fire when run for extended periods of time. I can't say I think either has what I would call sufficient levels of cooling, but the Kohler is better ventilated.

          Regardless of what you go with, I recommend you space the unit AT LEAST six feet from the side of the house, regardless of if code says you can go closer due to ratings or the material the side of the house is built from. You want that space for fire protection in case anything goes wrong. I'd also put the unit on the opposite side of the house from your bedrooms, even if that means additional fuel piping will be required. It's sooo much nicer to not here wrrrrrrr all night long during a power outage.


    2. Expert Member
      Akos | | #23

      My beef with most (all??) pad mounted residentail generators is that they run at fixed speed. For most this is 3600RPM to make 60hz power. No matter the load, the RPM doesn't change.

      Never mind the noise (even the best ones are pretty loud), this generally means that a 22kW generator supplying the typical 1kW to 2kW house load has terrible efficiency. This is less of an issue if running from natural gas but can add up on propane if you expect long outages. In that case, sizing for a smaller generator is the better option.

      If this is something that will need to run often and through the night, a nice portable inverter generator is better value, uses less fuel and way quieter.

      1. gusfhb | | #24

        22 kW does seem giant. I have noticed the increasing thirst on my portable as I went from 3.5kW[blowed up] to 5kW[used,blowed up] to my current 8kw

        The push to go all electric does run into a wall here. My smallest generator would run my boiler, but my largest one would probably run one of my 3 minisplits, if I was careful.

        Do they make larger inverter generators?
        At some point we want to get solar panels, and maybe some battery backup, starts getting complicated with generators etc

        [edit] I replied witha link, and it is awaiting moderation... short version, larger generators at low load are not that horrid

      2. Expert Member
        BILL WICHERS | | #26

        The reason the larger generators are all fixed speed is that the output frequency is directly related to the rotational speed of the generator based on the number of poles. It's a fixed mechanical relationship, so there is zero flexibility. Inverter generators are different in that they generate a high frequency (several hundred hertz typically), often three phase, AC, then they rectify that into DC and use an inverter to electrically generate the 60Hz output waveform. Since the inverter is now generating the 60Hz waveform electronically, the engine speed is no longer directly related to the output waveform, which allows for variable speed operation.

        I'm not aware of any larger permanently installed generators that are inverter type. There is no reason such a unit couldn't be made, I just don't know of any on the market. The largest inverter generators I've seen have been around 5kw or so, all portable units.

        Regarding fuel consumption, generators are least efficient at light load. As you increase load, you'll burn more fuel, but you'll get even more useful power out, so better efficiency. Typical generators use about half the fuel at quarter load as they do at full load, to give you an idea of how the efficiency changes with load. You always get best efficiency running up near full load as much as possible, but that increases thermal stresses on the generator. With the large gensets I design with at work, we try to keep average load up around 80% or so.


  9. gusfhb | | #25

    I went and looked and could find nothing larger than 5kW in inverter generator. I did find specs on a series of generators,%20MA,%20WI,%20IL,%20CT,%20OH,%20WA,%20NC,%20IN,%20VA,%20TN,%20GA)&utm_term=4581458812479254

    Implies a 16 percent increase in fuel use at low loads for over 50 percent larger generator, which is not so bad really.
    Guess what it really shows is that ICE engines are really inefficient no matter what....

  10. gusfhb | | #27

    I guess my link was icky.
    According to Cummins, going from 13kw to 20 kw the 1/4 load fuel usage increases 16 percent. 50 percent larger 16 percent more fuel use when not doing anything, so certainly not nothing, but for a part time use not the end of the world
    Actually I have to look again, but at low load[because 1/4 load of a larger generator is more kW] it looks like they are saying the larger is more efficient?

    Cummins RS13A-RS20A
    site doesn't like the link to the spec sheet, but see if I can attach it

    1. Expert Member
      BILL WICHERS | | #28

      It depends on load. Larger generators ARE more efficient than small ones but ONLY when operating up near full load. For light loads, you're going to be burning less fuel per kwh produced by running a smaller generator. The ideal scenario is to keep the average load as high as possible as percentage of the rated capacity of the generator while still allowing for enough extra generator capacity to handle cyclic loads (well pump, furnace blower, etc.). Note that "cyclic loads" are loads that run for a period of time and then shut off for a period of time, it is NOT the same thing as motor starting current or inrush (and note that the concept of "surge watts" is something of a joke in the commercial world, larger generators do not have ratings like that. We call "surge watts" "marketing watts".

      Anyway, for best fuel efficiency, you want to avoid oversizing your generator. As an example, with a 7.5kW average load (which is very high for a typical house), you will be better off from a fuel efficiency standpoint running a 10kw generator at 75% of capacity compared with running a 15kw generator at 50% of capacity, even though the 15kw generator might be more efficient near full load compared to the 10kw generator. You are concerned with AVERAGE loading more than PEAK loading for fuel efficiency. The downside with my example is that the 10kw generator would only have 2.5kw of available capacity for cyclic loads, while the 15kw generator would have 7.5kw of available capacity.

      I have found that the best fuel efficiency compromise is around a 7kw generator for most homes, but you'll have to do some load management to make that work. I would not advise such a small generator for a permanently installed system in most cases. I find that 12-15kw is usually a pretty good balance of fuel efficiency vs having enough available capacity to run whatever you want without worrying about load management. If you have an all-electric home, you might need a little more than that. It really comes down to what YOU need to run in YOUR home here.


  11. acrobaticnurse_Eli | | #29

    A couple weeks ago I got to see how well my small dual fuel inverter generator worked while plugged into my house via a power inlet with an interlock switch. A random storm knocked out power in a third of the city for 1-3 days. A 3000 watt firman dual fuel WH03242 generator ($800 at costco) enabled me to have lights, power my fridge and standalone freezer, keep our internet going, and power a small window AC. The Midea U shaped 8000 btu ac was perfect, starting out drawing only 100 watts per my kill a watt meter and never exceeding 450 watts while successfully cooling one bedroom and helping make the rest of the house a little more comfortable. 

    Since natural gas isn't available at my address and my house is all electric I went with the largest portable propane tank I could manage without a truck or a propane company membership, a Flame King 100 pound tank on wheels that can be used horizontally. After 24+ hours of use I went through less than half a tank, and today I picked up a second 100lb tank in preparation for hurricane season. Propane is great for never going bad so I can have it ready for the day or two per year I need it.

    Next I want to set up a power meter so I can tell in real time how close I am to the limit of my generator's production so I know if/when I can use higher draw items like the microwave. A 7-10kw 240 volt generator in combination with a soft start setup on my heat pump would enable me to practically act as if the power never went out, but for the limited amount of times the power goes out I'm not yet sure it's worth the additional cost. Per Duke power my average use when the power is on is 2-3kw per hour with a peak just under 7kw even when it's 90+ outside.

    My ideal setup would be a solark or EG4 all in one hybrid inverter with an ATS and 200amp passthrough that would enable me to automatically switch to battery power in the event of a power outage so quickly lights may not even flicker. Then once batteries are drained to a certain degree a generator could automatically be turned on via the solark to recharge the batteries. I would bring solar into the mix but am told I have too much shade.

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