Most Denver-area homes end up with a standby generator between 14 and 26 kilowatts. Where yours lands depends on what you want running during an outage, not on a rule of thumb about square footage. The most common mistake is buying a number someone quoted over the phone and finding out in the first outage what it will not run.
Myth: you need to power the whole house
You do not, and plenty of people are better off without it. A smaller generator that covers the things that matter costs less to buy, less to fuel, and needs a smaller gas supply. For most families those things are the furnace, the refrigerator, lights, internet, and a few outlets, plus a sump pump if you have one.
A 14 kW unit handles that list comfortably. The question to ask yourself is what a three-day outage in January would actually require, and what you could live without.
The air conditioner is usually the deciding load
The step up from 14 to 22 kW is mostly about cooling. When a central air conditioner starts, its compressor draws several times its running current for a moment. That spike, called inrush current, is what overloads a generator that looks big enough on paper.
A 22 kW unit runs most of a 3,000 square foot home, including a 3-ton central AC. A 26 kW unit is for larger homes or houses with more than one AC. If you want the AC covered, the load calculation has to account for that startup spike, not just the running number on the nameplate.
Altitude takes a bite out of the rating
Engines make less power at altitude, so a generator that is fine at sea level can come up short here. A good installer sizes for Colorado conditions and leaves some margin instead of buying right at the limit. This is one more reason to do an actual load calculation rather than copy a size from a brochure.
Natural gas or propane
Natural gas is the usual choice for homes on a gas line, because there is nothing to refill. Homes without gas service use propane from a tank. Either way, the gas supply has to be able to feed the generator at full load on top of everything else that burns gas in the house, and a larger generator needs more of it. Sometimes the answer is a larger gas line or a meter upgrade, and that is worth knowing before the pad is poured, not after.
What it costs installed
An 18 to 22 kW standby generator typically runs $9,500 to $15,000 installed in the Denver Metro. That covers the automatic transfer switch, the gas connection, the concrete pad, and the electrical and permit work. The spread depends on the size of the home, the load calculation, and the fuel.
The transfer switch is the part that matters most. It senses the outage and starts the generator within about ten seconds, then moves your house onto it and back again when power returns. No extension cords, no fuel runs in the dark. Most residential installs take one to two days, with the pad and prep first and the generator, electrical, and gas on the second day. Get a firm written quote after someone has seen the house and the gas meter, because a phone number for a generator is a guess.
What happens after it is installed
A standby generator needs a yearly service: oil, spark plugs, battery, air filter, and a test of the transfer switch under load. The unit also runs a short self-test on its own each week. Skipping the service is how people find out their generator does not start during the outage they bought it for.
If a full standby system is more than you want right now, a portable generator can still power the house safely through an interlock kit and an inlet box, which keeps power from feeding back onto the utility lines.
We install and service standby generators across the south Denver Metro. See our home generator page, or the pages for Castle Rock and Centennial. To size one for your house, call (303) 699-1417 or request a visit online.