In years past, the only entities able to afford emergency standby generators were hospitals, major corporations, and others with deep pockets.  Most of the units were powered by diesel engines, and those are inherently more expensive than gasoline-powered engines.  The other expense associated with diesel generators is the fuel supply:  both the fuel itself and the storage containers.  Some are above ground, but most are buried bunkers.  Because of the expense, most individuals could not afford to have an automatic standby generator.

In recent years, companies have solved the expense problem to some degree.  Although the units aren't necessariliy cheap, they're not the multiple tens of thousands of dollars they used to be.  In fact, based on recent cost increases with portable generators, they're not all that bad price-wise. The problem of fuel and fuel storage has also been solved.  Rather than burning a fuel stored in a tank, most home-sized standby generators run on natural gas or propane, regardless of whether they're air or liquid cooled.  This advance solves three problems:  the cost of installing and maintaining a fuel storage vessel, the up-front cost of filling that vessel, and the hassle of having to keep the stored fuel fresh.  As we all know, gasoline goes bad over time - and so does diesel.

More and more manufacturers are getting into the home standby generator business, but the name with the most longevity is Generac.  They offer several classes of machines in many wattage ratings to meet a wide variety of needs, including diesel generators for large commercial applications.  However, for home use, the two important classes are air cooled and water cooled engines.  Water cooled engines are more automotive-style engines using coolant and radiators to cool tlhe engine.  The other style is air-cooled.  These operate more like, for lack of a better analogy, a lawnmower engine, using circulated air to cool the engine.  Obviously, water cooling allows for larger engines, more horsepower, and ultimately more generating capacity.  But it also means more expense.  Unless your wattage requirements are high enough to require a liquid cooled engine, an air cooled unit will probably suffice.  Generac offers multiple models of air cooled standby generators, from 8 kW up to 20 kW (18 kW for natural gas, as propane has more BTUs by volume than natural gas).

Standby generators offer many advantages over a portable generator.  Here are the main advantages:

• Permanently installed - no need to dig it out of the back of the garage
• Completely automatic
• Runs on natural gas
  • Fuel is inexhaustible as long as you have natural gas pressure
  • No fuel to store or maintain
• Quieter than portable generators
• Switches and plugs work inside the house
• No extension cords
• More powerful than portables
• Automatically exercise themselves on a set schedule

When power fails, the automatic transfer switch senses the utility power loss and springs into action.  First, it flips a switch to disconnect your home from the utility power grid so as not to backfeed power onto the grid.  Secondly, it starts the generator and lets it warm up and run for a few seconds.  Third, it flips another switch and comes under load as it begins supplying electricity to the house.  The whole house - or, if you have a smaller unit, selected circuits.  When utility power is restored, it flips the switches to place the house back on the grid and remove the load from the generator.  It then will cool the generator down for a small amount of time, then automatically shut down.  Everything is automatic, and power can be restored by the generator in as few as 10 seconds after utility power fails.  No more stringing extension cords, no more having to drag the generator out of the back of the garage, and no more having to keep fuel around to run it.

Another huge advantage of a standby generator is their power capacity.  The most common portable generators produce somewhere in the neighborhood of 5,500 watts (5.5 kW), and they do it on around 10 horsepower produced from a single-cylinder engine.  The standby unit I'm interested in for my home is an 18 kW unit, and it makes that power with a two-cylinder v-twin engine rated at 39 horsepower.  But how does that translate into what you can run with the unit?  In short, with that much power capacity, I will be able to run everything in my home that I might need to run in an extended power outage.  Everything.  Including my big central air conditioning units!  No more having to mess with portable or window air conditioners.  This generator has enough capacity to run one, if not both, of my central air units along with everything else I might want to run on it:  fridges, freezer, computer gear, entertainment system, fans, lights, etc.  Everything.  Pretty darned sweet!

If you want to run your central air unit, you have to make sure that you have enough generating capacity, and you need to know the tonnage of your system.  My systems are 3 tons each.  Everything I've read recommends  a minimum of 17 kW to run a 5 ton unit, so I should have enough extra capacity to run at least one of my 3 ton units along with everything else I need to run.  It will take some management:  when I'm downstairs, I'll turn the downstairs unit on and turn the upstairs unit off.  When I'm upstairs, I'll turn the downstairs unit off so I can run the upstairs unit.  A larger capacity generator would be capable of running both of the units at the same time; however, larger units would put me into the water-cooled class, and that adds quite a bit of expense.  The 18 kW unit is the largest air cooled unit Generac makes.  But if you have the need - and deep enough pockets - you can definitely get a unit large enough to run multiple central air units.

I'm heavily considering the investment in a whole house standby generator.  They are expensive:  the unit I'm looking at right now sells for anywhere between $4,500 and $5,200, and includes the automatic transfer switch.  On top of that will be plumbing for the natural gas supply line and electrician's fees to wire it all up.  I'm anticipating a total investment of somewhere around $6,500 - $7,000 for the unit and installation.  It is pretty steep, but comfort, convenience and peace of mind all come with a price.

If I decide not to go this route, I'll definitely be installing a manual transfer switch so I can hook up my portable generator to the house with a single cord.  I won't be able to power everything, but it will still be more convenient than having to mess with all the extension cords.  I've got a couple of articles dedicated to portable generators and manual transfer switches if you're interested in checking them out.

UPDATE 8/9/2010

I have signed a contract with Quality Generators here in Houston for a Generac Guardian 20/18 kW air cooled, natural gas-fueled whole house automatic standby generator.  They actually poured the concrete pad for the unit today, and I'm expecting unit installation within a couple of weeks.

Update 8/30/2010

Generator installation is complete!  All plumbing and electrical work is finished, and we test ran the unit today, including house load testing.  The generator is now on duty and on standby!  See my generator installation article for the stories and photos relating to the generator installation.