Generator for House

I'm thinking of buying a generator for the house I am buying. Any suggestions on how to size the unit and other manufactures to look at. I went to Generac's web site and for my size of home and including the well and dryer on the unit it said I needed a 20Kw generator. That seems a bit large to me so I'm just trying to get some advice. Is there any difference in performance with gas powered vs NG powered units?

 

Generac is a reliable product. In an emergency situation like you would be in while using a generator, there are certain amenities that you can do without and not have energized via the generator. The dryer is one of them. Water heater is another. You will need to pin point your priorities, THEN figure the size. Gas powered you will have to fill up in possibly inclimate weather after shutting it down to cool. NG, or Propane is more reliable, propane probably being the best since NG supplies can be disrupted, while your propane tank is full, hopefully.

 

Decide what you want to power during an outage. For many people the essentials are important...sump pump, cellar and kitchen lights, refrigerator and/or freezer and perhaps the furnace depending on your location. Others want the whole house and all the rimming to be powered. Add all the wattage requirements and go from there.

A natural gas unit is very good, can supply the whole house, is reliable, safe, automatic, and virtually maintainance free, and expensive. Will self test on a daily or bi-weekly basis. Usually requires a professional to install and requires yearly maintenance from installers. Will usually require permits from the town and is non-portable.

A gasoline unit is cheaper, less safe, must be checked on as fuel and oil is used. It's noisy. Will require you to turn it on as needed. Needs regular maintenance especially as it gets older. If pull start must be kept ice free in winter. Should be started periodically and supplied with fresh gasoline on a regular time table. Should be used with a transfer switch if used to power more than one appliance in the house. And must not feed back into power main or circuit braekers. It usually is portable. Must be kept outside away from windows and doors during use. Requires a long , heavy duty extension cord. Most can provide 120 and 240 volt.

If needed because of health reasons or life support then the NG is a no brainier.

With that said I use a gasoline unit with a self installed transfer box and it provides power to sump pump, freezer, lights to most of house and a few other items as needed. Cost less than $1000 including transfer box. I'm very pleased with it.

As a side note...If you find yourself needing to bale a sump pit due to an outage or doing some activity that can injure you because of lack of power then get the generator. It's worth every dollar compared to hurting yourself. Just be sure to use it safely.

 

Do a residential load calculation. You can download an Excel template from Mike Holt to do that (it's the third item from the bottom). 20kW will probably back up all of a standard small-to medium-sized house w/o central A/C.

 

NG are reliable and relatively low maintenance with a near endless fuel supply. Gasoline generators are a maintenance nightmare. Do you have a place to store several 5 gallon gas cans with fresh gas; fresh meaning, not over 60-90 days old.

 

On my home I installed a 12 KW propane generator, and an Automatic Transfer switch. All my cooling, heating and dryer were propane so their load on the generator was low. In addition to those items I had some lighting, kitchen microwave and garage lights and opener. I like having the ATS because it will exercise the generator each month so when it is need, you know it will work. My home is also in cold country in the winter and I needed to be sure and have heat if power failed when we were away. I like propane because the maintenance on the generator's engine is much less than a gasoline powered unit and I did not have to store or treat gasoline if the the generator was not needed often. Along with the ATS I installed two panels, one normal and one emergency. These panels were side by side with a conduit between them so I if needed to add or remove a load from the emergency panel I could do so easily. Unless you outages typically last for days, you really can get by with a few key items and a reasonably sized generator. The only other thing I can think of is depending where you live, elevation will have an effect on generator capacity. My home had a 200 amp service and I was at 4000ft+ elevation.

 

How long do you anticipate power outtages to last and how comfortable do you want to be?

If power tends to go out for just a few hours then you can get by with a pretty small generator. Something to run a few lights and maybe your tv for entertainment. If planning for the power to be out for a day then you might want to go larger and get something that can also run your furnace or AC and refrigerator. To help keep the size requirement you can turn off unused breakers or unplug your refrigerator when running the AC to keep the peak load down. Then if you tend to have long outages like I do from hurricanes or winter ice storms you want something big enough to run the AC and fridge and well pump. When the power is out for 5 or 7 days you start to need more and more things like the ability to wash clothes or take a shot shower.

 

My well, dryer, and AC compressor. I'd think would be the biggest draw. Maybe the furnace motor not sure. Other then that I don't think the load would be that great.

 

This is a fun calculator to size units for different loads.

Wattage Calculator

Motors are the hardest things for gens to start. AC compressors especially. It has to do with something called surge or inrush current. Hard start kits for motors can lessen the problem.