I’m considering buying a backup generator. I have street LNG to the house. I assume since it always has pressure, as long as suppliers don’t shut it off, I’d be ok. But if there were a period of extreme social disruption, suppliers may do just that, in which case the unit would be useless. I could go with a liquid fuel unit, but don’t really want to store fuel. What’s your opinion on the disruption problem? The 1st on-line sizing calculator I found says I need a 17.5 kW generator.
I was a boy-scout, so I always believe in their motto – “Be prepared”. Having said that, I do not know how big your house is, but a 17.5 kW generator is REALLY big for a home, unless it is all electric with 2 or more heat pumps. We have found a generator in the 8 kW range will handle everything in a typical home except air conditioning or electric heating. This size unit will easily power all lights, kitchen appliances, big screen TV and audio equipment, freezer, micro-wave oven, and well pump. It will also power your furnace fan if you have gas heat, but will be on the edge if you also try to power a heat pump or AC unit. Going up to a 12 kW generator will usually power all of the above, plus one fair sized heat pump or air conditioner.
I have many clients with homes having 4 or more heat pumps or AC units due to the large size of their home. I always tell them to decide what parts of the house they really need during an extended emergency and only heat or cool those spaces. This will not only reduce the size generator needed, but also the fuel since most generators use almost the same fuel at half loaded as full, so a over-sized generator only lightly loaded will usually use more fuel than a generator sized better to match the load.
As far as emergencies go, usually natural gas from the local utility is more reliable and available during storm related power outages, but there are times during line breaks or peak loads in the winter when line pressures drop. Any generator designed for natural gas can be easily converted over to run on propane. The Kohler line which I favor has a manifold block that has 2 pipe plugs, which are moved from one port to another to change over from propane to natural gas. It would be fairly easy to make a piping arrangement to allow a quick disconnect from the city line to a line from a underground propane tank, but I would make sure you are using a piping connection that must be first disconnected from one supply before connecting to the other or you could have a very dangerous situation if high pressure propane gas passed into the lower pressure city gas line.
If this is a real concern why not just keep the generator connected to a underground 500 or 1000 gal propane tank? Propane fuel does not go stale like gasoline, and you generator will always be ready as long as you run it every few weeks to keep it lubricated and battery charged.