Key takeaways
- Load bank or exercise: diesels need regular load. Light loads cause wet stacking.
- Cooling and filters: coolant, oil, fuel filters and air filters are the main consumables.
- Cold weather: block heaters and fuel treatment help startup.
- Transfer switch: required by code for permanent connection.
- Permits: large fuel tanks and stationary generators may need local permits.
A 15 kVA diesel generator delivers about 12 kW at the common 0.8 power factor, or a full 15 kW if the set is rated at 1.0, so check that number before you compare models. For a US single-phase home, the Kubota Lowboy Pro GL14000 (12 kW prime, 14 kW standby) and the Generac Protector 15 kW are the practical picks; outside the US on 50 Hz power, the Kubota SQ-1150 is a 15 kVA reference set. Rating basis (prime or standby), phase and voltage matter more than the label on the box.
Our top picks
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Quick comparison of 15 kVA-class diesel generators
| Pick | Best for | Key specs (per maker listings) | Price range |
|---|---|---|---|
| Kubota Lowboy Pro GL14000 | Best US home set | 12 kW prime / 14 kW standby, single phase 120/240V, 60 Hz | Premium |
| Generac Protector RD01525 | Best automatic standby | 15 kW, 1800 rpm, liquid cooled, single or three phase | Premium |
| Cummins C15D6 | Best alternative standby | 15 kW standby, liquid cooled, 1800 rpm | Premium |
| Kubota SQ-1150 (50 Hz) | Best for 50 Hz regions | 15 kVA / 15 kW prime, 16 kVA standby, V2203 engine, 100 L tank, 5.5 L/h at full load | Premium |
| SDMO K12U IV (Kohler engine) | Best for three-phase 480V sites | 12 kW / 15 kVA standby, 11 kW / 13 kVA prime, 340 kg dry | Upper-mid to premium |
kVA vs kW: the number that trips up most buyers
kVA is apparent power; kW is real power. The conversion is kW = kVA multiplied by the power factor. Most diesel gensets quote 0.8, so 15 kVA equals 12 kW. That is the SDMO listing: 12 kW and 15 kVA standby. Some sets, like the Kubota SQ-1150, are rated at a power factor of 1.0, so the same 15 kVA equals 15 kW. A 15 kW set is therefore about 25 percent stronger than a 12 kW / 15 kVA set, even though both are called “15.” Always compare the kW figure and whether it is prime or standby.
| Rating | Meaning | Use |
|---|---|---|
| Standby | Maximum for emergency use, limited hours | Storm backup |
| Prime | Continuous variable load with unlimited hours | Off-grid or long outages |
| Continuous | Constant load, 100 percent | Industrial use |
For storm backup, standby ratings are fine, but if you expect outages longer than a few days, size to the prime rating.
Best US home set: Kubota Lowboy Pro GL14000
Kubota’s GL14000 is 14 kW standby and 12 kW prime on single phase at 120/240V and 60 Hz, which matches typical North American residential service. The related DGK15F lists 13.2 kW standby and 12 kW prime with sound around 65 to 67 dBA. These sets use Kubota diesel engines known for long service intervals.
Who it suits: homeowners who need a quiet, enclosed set for a larger house. Main trade-off: premium cost, plus installation, a transfer switch and a fuel plan.
Best automatic standby: Generac Protector RD01525
The RD01525 is a 15 kW diesel standby set at 1800 rpm and is available in single or three phase. Generac lists a starting price in the mid-teens of thousands before installation, so budget for a pad, transfer switch and labor. At 1800 rpm, a four-pole set tends to run quieter and cheaper than higher-speed sets of the same size.
Main trade-off: its 15 kW rating is a standby figure, so for long outages watch load levels and the hour limits in the spec sheet.
Best alternative standby: Cummins C15D6
Cummins lists the C15D6 as a 15 kW standby set with liquid cooling at 1800 rpm. It is worth a quote if a local Cummins dealer offers service. Verify voltage and phase options before ordering.
Best for 50 Hz regions: Kubota SQ-1150
Outside North America, the SQ-1150 is a 15 kVA reference. Per Kubota, it has a V2203 four-cylinder engine at 1500 rpm, a 100 liter tank and burns 5.5 L/h at full load. That implies about 18 hours at full load from the tank. It is a 50 Hz set, so US buyers should not choose it for household use.
Best for three-phase 480V sites: SDMO K12U IV
This SDMO set uses a Kohler KDW1404 engine and is listed as 12 kW / 15 kVA standby on three-phase 480/277V at 60 Hz. It suits workshops, pumping stations and light commercial buildings. A typical US house is single-phase 120/240V, so do not buy this for a home unless you have a matching service.
Fuel burn and tank sizing
Use the Kubota figure of 5.5 L per hour at full load as an example. That is about 1.45 gallons per hour. At 75 percent load, expect roughly 4 L/h (about 1.1 gallons per hour). For a 72-hour outage: 72 multiplied by 1.1 equals about 79 gallons. That exceeds most built-in tanks, so plan for an external tank or refueling logistics. At half load, consumption drops to roughly 0.8 gallons per hour, or around 58 gallons for 72 hours.
Sizing a 15 kVA set to your home
| Load | Running watts (typical) | Start surge |
|---|---|---|
| Refrigerator | 150 to 700 | Up to 2,200 |
| Well pump (1 HP) | 1,000 | 3,000 |
| Central AC (3 ton) | 3,500 | 7,000+ |
| Electric water heater | 4,500 | None |
| Furnace blower | 500 to 800 | 2,000 |
| Lights and electronics | 500 to 1,000 | None |
Add the loads you want to run at once. For example, a fridge, well pump, furnace, central AC and lights come to about 6,000 running watts, with a start surge that can pass 8,000W if motors start together. A 12 kW set handles that, but a 15 kVA set at 0.8 power factor has no room to spare if you add the water heater.
Ownership realities
- Load bank or exercise: diesels need regular load. Light loads cause wet stacking.
- Cooling and filters: coolant, oil, fuel filters and air filters are the main consumables.
- Cold weather: block heaters and fuel treatment help startup.
- Transfer switch: required by code for permanent connection.
- Permits: large fuel tanks and stationary generators may need local permits.
Which 15 kVA diesel generator should you buy?
| Your situation | Pick |
|---|---|
| US single-phase home | Kubota GL14000 or Generac RD01525 |
| Want a second brand quote | Cummins C15D6 |
| 50 Hz farm or site outside North America | Kubota SQ-1150 |
| Light commercial three-phase | SDMO K12U IV |
Frequently Asked Questions
How many kW is a 15 kVA generator?
At a 0.8 power factor it is 12 kW. At a 1.0 power factor it is 15 kW. Check the spec sheet.
Can a 15 kVA diesel generator run a whole house?
Often yes for homes up to about 2,500 square feet if you manage large loads, such as a single central AC unit. Add up your running and surge watts first.
How much does a 15 kVA diesel generator cost?
Prices commonly range from the high single-digit thousands for basic sets to over twenty thousand for enclosed brand-name units, before installation. Shop by rating, phase and warranty, not price alone.
Is prime or standby rating better?
Standby is fine for short emergencies. Prime is better if the generator will run for long periods or support off-grid use.
Do I need a transfer switch?
Yes. A transfer switch or interlock installed by a licensed electrician is required to connect safely and prevent backfeed.
