Four questions to consider when choosing a home generator

A business colleague recent tweeted a question about choosing a home generator. He was concerned about recent power outages in New England and worried that they would continue in the upcoming months and years. He was looking at options to protect his home in the case of a significant outage. I had recently considered adding a generator and wanted to share some learnings. The process is not that complex but there are four key questions that need to be considered:

1. Generator size

There are two differing perspectives on this question.

The first strategy is to use a very large generator (someone recommended a 20Kw to me). The benefit of this approach is that the large unit would power everything in the house and so you could run all your appliances including air conditioners, electric dryer and even electric stove without a problem. However, there is a trade-off. The larger generator typically means higher cost, more noise and increased fuel consumption.

The alternative approach is to choose a smaller generator (~10Kw). These units will not power the entire house, but rather are used to power critical systems such as heat, lighting, refrigerator and selected outlets. These smaller units will not power electrical intensive devices like electric dryers, stoves or ovens. However, they are less expensive to purchase, often are smaller in size and use less fuel. The installation process can also take a bit more work since someone has to identify which circuits to include and exclude. If you are considering this approach, you should review your circuit breakers to understand which you will power with the generator and which you won’t. These circuit choices will impact the generator size you need.

2. Manual or Automatic

Power outages can happen suddenly and so a generator needs to be prepared to come online rapidly. A big question is how the generator is started. Common options include automatic start, manual electric start (push a button or turn a key) or manual pull start. In general, the first option requires the least intervention (actually none), while the second two require the owner to start the generator manually. Obviously, the automatic option is extremely convenient and beneficial because it will start regardless of the hour and whether anyone is available. However, you will typically pay a premium for this feature and you rarely find it on anything but dedicated home generators. The price difference between the first option and the second two can be orders of magnitude different and so this really comes down to a question of budget versus convenience.

On a side note, with whatever generator your get, you will need an electric transfer switch. This device will enable your generator to power the house and will also disconnect your house from the electrical grid. This is critical because without it, your generator could push power back into the grid which could hurt power workers trying to fix the lines. There are a variety of switch options available some of which are manual and others that are automated. As you can imagine, the automatic start generators typically come with automatic transfer switches while manual generators often require you to purchase a separate manual or automatic transfer switch. Clearly, if you have a manual generator you are probably better served with a manual transfer switch since this is significantly less expensive than an automatic one and manual intervention is required to start the generator anyway.

3. Fuel

The next question is which fuel to use to power the generator. The choice of fuel can vary widely with the most common options including natural gas, propane and gasoline.

Natural gas is a good option for the homeowner who is already using this fuel. It is relative easy to plumb the generator into the existing natural gas line. Gas is also helpful because it does not require manual fuel deliveries or pickups and can effectively run the generator in perpetuity. Obviously, you would need a competent plumber to connect the generator and the cost can be significant. Note that most dedicated home generators support natural gas.

The next option is liquid propane (LP). Propane is an equally powerful source of fuel as natural gas although it requires external tanks. Thus, when installing a generator using LP, you also need to think about installing propane tanks and tank sizes. Bigger LP tanks extend run times, but are larger and can be more difficult to place and hide. Conversely, smaller ones are easier to conceal but will provide shorter run times. Additionally, LP tanks need to be refilled and so if a significant outage occurs, you may need a propane supplier to visit your house. This could be an issue if the roads are blocked or otherwise inaccessible. (This should factor into the tank size since larger tanks will allow for longer run times and thus fewer fill-ups.) Note that most home generators offer the ability to support either LP or natural gas and represent a good option if you are unsure if you will change fuel in the future.

The final option is gasoline. Obviously this is an extremely common fuel and can easily be retrieved at any gas station. The challenge is that gasoline-based generators have smaller fuel tanks thus requiring more frequent fill-ups. Thus, a gas generator owner would either need to have a significant store of gasoline at their house or make fairly frequent trips to the gas station. This can also be problematic if the gas station is inaccessible or worse, is sold out of gas. For example, I have a friend who has a gas generator that works well, but it only delivers about 10 hours of run time and so he needed to refill it at least twice a day. He was okay with this requirement, but not all users may agree. The benefit of this fuel is that it is ubiquitous since there are gas stations everywhere. Similarly, gas generators tend to be much less expensive than their natural gas and LP counterparts.

The choice of fuel is significant and there is no right choice for everyone. Clearly, natural gas provides the least human intervention with automated fuel availability; however, it requires that the house already have the fuel. LP provides shorter run times than natural gas and an external tank, but the larger tank sizes (than gasoline) can provide power for extended periods. Additionally, refueling from a propane company simplifies the process of refueling, but still introduces risk. Finally, gas provides the most ubiquitous and inexpensive fuel source; however, it requires significant owner intervention to ensure that the generator is fully fueled and running.

4. Budget

The final issue is budget. Regardless of the route you take, a transfer switch is required and so you will need to pay an electrician for installation. However, the scope and complexity of the job can vary widely. Often the biggest cost is the generator and there is a huge price range. You can purchase an inexpensive portable gas generator for as little as $500 while a fully automated 20Kw home generator can run $5,000 or more. Clearly, the more you spend, the bigger and more automated the solution becomes, but the largest options may be beyond the reach of many. You also need to keep in mind other installation costs which can include plumbing the natural gas line or purchasing, installing and filling LP tanks and pipes. Finally, there may also be a cost to prepare a location for the generator and/or fuel tank including leveling ground and preparing a pad.


In conclusion, there are many different elements to consider when purchasing a home generator. The options range from a quick and inexpensive approach with lots of manual activity to a fully automated whole house unit that will essentially run forever. The choice of option really comes to budget and desired functionality.

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