How do I buy a generator for my house?
May 27, 2010 6:40 AM   Subscribe

Help me buy a generator! Degree of difficulty: 5-ton AC.

I'm in South Florida and hurricane season is approaching. The part of the power grid that we live on is small enough, in terms of number of households, that we're always the last one that gets responded to.

I know nothing about buying a generator and I'm officially entering my research and due-diligence phase.

Our goals for power include:
1. 5-ton AC
2. Standard fridge
3. lights, not necessarily throughout the house.
4. microwave

I've seen portable generators that go up to 12,000 starting watts but am having trouble determining if that's enough for my house(modest, 3BR 1.5bath).

anything else is bonus - like enough to keep the phones and laptops charged, etc. I'd also rather have too much power than not enough. Can I get by with a larger portable unit, or am I looking at one of the permanent, automatic switching models?
posted by neilkod to Grab Bag (9 answers total) 2 users marked this as a favorite
If you want to be able to run the house as if it were still getting power from the grid, I think you're looking at a significantly larger generator. One that can handle a 12 kW surge can probably only sustain 8000 watts, which might be enough to run the AC but nothing else. 8000 watts at 220v is 36 amps. What size breaker is on your AC circuit? Your whole house could easily have 200A service.

The fridge, lights and microwave ought to be very doable with a portable unit, and the laptops and phones will be no problem at all. Central air is a lot to ask.

I do not live in a hurricane-prone area, and my neighbors do not keep generators. My experience with them is limited to a fishing cabin I visit occasionally.
posted by jon1270 at 7:54 AM on May 27, 2010

My brother (south Louisiana) suggests a 10 or 12k unit. It may be slightly overkill, but the price difference between an 8 and a 12 is not significant. He suggests Kohler or Generac. His Generac is a 15kw portable and it's done admirably through three major storms. Buy it now, before storm prices kick in. My bro knows of which he speaks, email me with any follow up questions and I'll pass them on to him.
posted by ColdChef at 8:12 AM on May 27, 2010

A co-worker here in Georgia went through a similar process after he twice lost power for a week at a time, once to a tornado, once to an ice storm. The advice he got, from one generator specialist after another: Forget being able to run the AC. Just put it out of your head. There are generators that are made for that kind of load, of course, but for the average homeowner, they're simply too expensive. He was quoted somewhere on the order of $100,000 for the unit and installation, and then 2-3000 per "event" in diesel fuel - assuming you can get diesel delivered at all in a post-hurricane disaster situation.

My advice would be to get a generator big enough to run your fridge and few nice fans, and enjoy a nice cold drink while your AC is out.
posted by deadmessenger at 8:22 AM on May 27, 2010 [1 favorite]

If you're having trouble finding a generator that will power your 5-ton AC, why not keep a small energy-efficient window unit in storage to use in these situations? You could keep one room chilled (probably your bedroom) for when you absolutely need to cool off.
posted by Willie0248 at 8:35 AM on May 27, 2010

I know that in SC it was popular to buy used construction site mobile generators. Easily enough to run your entire house. They're mobile, run on diesel, and started around $10k or so (which was far above what I was willing to spend).
posted by anti social order at 10:52 AM on May 27, 2010

The air will be hard to run. You can find some gas based ones, but they won't be efficient. You will need to go to a diesel one at that point. Check the label on the compressor to see if it lists the LRA. The locked rotor amp draw will give you an idea of the worst case. It can easily be 3-4 times the running current.

I would also agree to get a window unit if needed. Then you can get a smaller generator.

My suggestion is to shop for a generator that runs on natural gas and has an automatic transfer switch. They are much easier to deal with. Generally lower maintenance too. Most will automatically run through an exercise cycle. They start up and power the home without you being there. You don't need to keep fresh gas around.
posted by Climber at 11:41 AM on May 27, 2010 [1 favorite]

I use a generator quite a bit at home, but on a much smaller scale. From what I've gleaned from that as well as working in the renewable energy field, I would agree with the suggestion that you buy a window AC unit, and scale back your desire to run your entire house as you normally would. I don't know what kind of wattage a 5 ton AC unit uses, but I can imagine it's not small.

For ease of use and low maintenance, an LP (natural gas) fueled genny is the way to go. Storing (and maintaining) gasoline or diesel on site in preparation for the once-per year (or less) you're going to use this is a headache. Climber's suggestion makes a lot of sense. You want one that will start up on its own once a week, and run for 10 minutes or so, to keep the machine in good nick. If you're not technically minded, and just want it to work, you might think of a service contract- somebody who comes and checks it every so often- changes the oil etc. The brands I hear most often for people with your needs are Kohler, Generac, and Onan.
posted by MacChimpman at 12:11 PM on May 27, 2010

Just a rough guess puts your AC at 7-8kW, all on it's own. (probably higher starting draw, plus circulation fan). A quick google shows ~ $6,000 here (scroll down). for a 12kW unit. Please check the nameplate of your AC unit and find out what the startup current draw is, since you will need the capacity to meet that. I'm not sure if 12kW is enough. I'm with others stating that you need to get a window or split system in this case.

Charging laptops / some lights etc. is very minor compared to this, especially if you switch your lights to 20W compact fluorescent bulbs (~100W equiv) etc. You can get an 800W or 1KW portable unit which will do your basic lights / laptops / tv. etc.
posted by defcom1 at 5:13 PM on May 27, 2010

The contractor that you hire to hook up the generator should be able to let you know how big of a load you need to handle.

Seriously, call a contractor or at least go to Home Depot or something like it. This is not a DIY project.
posted by squorch at 7:35 PM on May 27, 2010

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