The Kohler 20RESA is a 20 kW air-cooled home standby generator that was sold on its own, with no transfer switch in the box. That one detail is what sets it apart from its better-known twin, the 20RESAL, and it shapes almost every question owners ask about it.
Which transfer switch does it use? Can it back up the whole house? What is the RDC2 controller, and how is it different from the DC2? And now that Kohler has moved on to the 20RCA, what should you do with a 20RESA that is ten years old or more?
This guide answers those questions. It focuses on the things that are specific to the 20RESA: the switch choices, the controller and the buying decisions. Ratings and fuel data come from Kohler’s specification sheet, and controller details come from Kohler’s operation manual. We have not tested this generator.
Kohler 20RESA at a glance
The 20 kW generator you pair with the switch your home needs
Figures come from Kohler specification sheet G4-210 and operation manual TP-6804.
Quick answer
The Kohler 20RESA is the generator-only version of Kohler’s earlier 20 kW air-cooled standby unit. It makes 20 kW on propane and 18 kW on natural gas, uses the 999 cc CH1000 engine and has the RDC2 controller. It was sold without a transfer switch, so installers paired it with a 100-amp, 200-amp or service-entrance switch to suit the home. The 20RESAL is the same generator bundled with a 200-amp RXT switch. The current replacement is the Kohler 20RCA.
How we put this guide together
We have not tested this generator. Ratings, fuel use and sound levels come from Kohler specification sheet G4-210 for the 14 kW and 20 kW models. Controller behavior and maintenance intervals come from Kohler operation manual TP-6804 (June 2015), which covers the 20RESA with the RDC2 controller. Transfer switch families come from Kohler’s current website. All were checked in October 2026. Your installer, your nameplates and your own manual take priority.
In this guide
- What Is the Kohler 20RESA?
- Why Sell a Generator Without a Switch?
- Kohler 20RESA Specs in Brief
- Transfer Switches for a 20RESA
- Can a 20RESA Run a Whole House?
- The RDC2 Controller
- Fuel Use and Gas Supply
- Maintenance in Brief
- Buying a Home With a 20RESA, or a Used One
- Keep It or Replace It?
- Replacement Options
- Common Mistakes With a 20RESA (and the Fix)
- Pro Tips for 20RESA Owners
- Real-Life Scenarios: Which Setup Fits?
- Kohler 20RESA FAQ
- Your Kohler 20RESA Checklist
What Is the Kohler 20RESA?
The 20RESA is a permanently installed generator for homes. It runs on natural gas or propane, sits outside on a polymer base and starts automatically when utility power fails.
Kohler sold this generation in two ways.
| Feature | 20RESA | 20RESAL |
|---|---|---|
| Generator | 20 kW, CH1000 engine | The same |
| Transfer switch | Not included | RXT 200-amp, included |
| Controller | RDC2 | DC2 |
| Setup prompts at power-up | Asks for date, time and exerciser | Does not prompt |
| Who it suited | Homes that needed a specific switch | Homes that wanted one complete package |
The generator itself is the same machine. What differs is the controller and what came in the box.
You may also see the names 20RESC and 20RESCL. Kohler’s operation manual covers those models alongside the RESA and RESAL, and they follow the same naming rule: the L means a switch was included.
Why Sell a Generator Without a Switch?
It sounds like less for your money. In practice it gives the installer room to do the job properly.
Homes differ. One has a 100-amp panel and only needs a few circuits backed up. Another has 200-amp service and the switch has to go outside, next to the meter. A third has 400-amp service split across two panels. A single bundled switch cannot suit all three.
With the 20RESA, the dealer chose the switch after looking at the house. That is why two 20RESA installations on the same street can look quite different.
Key insight: the generator decides how much power you have. The transfer switch decides where that power can go. On a 20RESA, the second choice was left open on purpose.
Kohler 20RESA Specs in Brief
| Spec | Kohler 20RESA |
|---|---|
| Rating on propane (LP) | 20 kW, 83.3 amps |
| Rating on natural gas | 18 kW, 75 amps |
| Voltage | 120/240 V, single phase, 60 Hz |
| Engine | Kohler CH1000, V-twin, 999 cc, hydraulic valve lifters |
| Engine power | 30.9 hp on LP, 27.1 hp on natural gas |
| Line circuit breaker | 100 amps |
| Sound level | 64 dB(A) weekly exercise, 69 dB(A) full speed, at 7 meters |
| Size | 48 x 26.2 x 29 inches |
| Fuel inlet | 1/2 inch NPT |
| Battery | 12 volt, group 51, 500 CCA minimum, bought separately |
| Warranty when new | 5 years or 2,000 hours |
For a deeper look at the shared specifications, fuel tables and the SA bundle codes, see our guide to the Kohler 20RESAL generator. The numbers there apply to the 20RESA as well.
Transfer Switches for a 20RESA
An automatic transfer switch, or ATS, sits between the utility, the generator and your home’s wiring. When the grid fails, it disconnects the house from the utility and connects it to the generator. When the grid returns, it switches back. Kohler calls it the brain of the system.
It also does a safety job. By breaking the link to the utility before it connects the generator, it stops generator power from flowing back into the power lines, where it could injure line workers.
The Kohler switch families
Kohler’s current website lists two residential families.
- RXT switches. Offered in 100, 200 and 400 amps, in standard and service-entrance versions. Kohler’s spec sheet says the RXT is designed for use only with Kohler generators that have the RDC2 or DC2 controller.
- RDT switches. These include a 200-amp service-entrance model with a 42-space load center built in.
With an RXT, the generator’s RDC2 controller runs the switch. The two talk to each other, so the generator’s display can show switch faults, and the controller can run a loaded exercise that actually transfers the house.
Which type does your home need?
| Your home | Typical switch | What gets backed up | Notes |
|---|---|---|---|
| 100-amp service, or only key circuits needed | 100-amp switch with a load center | Chosen circuits only | The simplest and often the cheapest install |
| 200-amp service, switch can go after the main breaker | 200-amp standard switch | The whole panel | Large loads may need managing |
| 200-amp service, switch must be at the meter | 200-amp service-entrance switch | The whole panel | Replaces the main disconnect |
| 400-amp service with two 200-amp panels | A 400-amp switch, or one switch on one panel | Everything, or one panel | Needs careful load planning on a 20 kW unit |
Service-entrance rated means the switch contains the main disconnect and is approved to be the first thing after the meter. It is common where the meter and main breaker are outside.
A load center is a small breaker panel built into the switch. Selected circuits are moved into it, and only those circuits get generator power.
How to find out which switch you have
Go to the switch, not the generator. Its nameplate shows the model number, the amp rating and whether it is service-entrance rated. Take a photo. A dealer needs that model number for parts and service, and so will a future buyer of your home.
Look, do not open
You can read the nameplate on the outside of the enclosure. Do not open the transfer switch. The utility side stays live even when the main breaker in your panel is off, and there is no safe way for an untrained person to work inside. Installation, repair and replacement belong to a Kohler dealer or a licensed electrician, with a permit where required.
Can a 20RESA Run a Whole House?
It depends on the house, and on what you mean by “whole”.
The 20RESA supplies up to 83.3 amps on propane and 75 amps on natural gas. A 200-amp panel can, in theory, draw far more than that. In real life it almost never does, because you do not run everything at once.
A 20 kW generator comfortably covers lighting, refrigeration, a gas furnace, a well pump, the kitchen and a central air conditioner. Trouble starts when several large electric appliances run together: two air conditioners, an electric range, an electric dryer and an electric water heater.
Load control is the answer
Kohler offered a Load Control Module for this generator. According to the spec sheet it has four power relays and two HVAC relays. It holds back lower-priority loads when the generator is busy and lets them run when there is room. With load control, a 20 kW generator on a 200-amp switch behaves well. Without it, the generator can shut down on low speed or low frequency when too much starts at once.
Tip: plan around the fuel you use
On natural gas, the 20RESA is an 18 kW, 75 amp generator. If your home is on natural gas and your installer sized everything around 20 kW, some of your dimming lights and nuisance shutdowns may trace back to that 2 kW gap.
Our Generator Size Calculator helps you add up loads, and our guide to whole-house generators explains load management in plain English.
The RDC2 Controller
The RDC2 is the main thing you interact with on a 20RESA. It is a fuller controller than the DC2 on the RESAL, with a menu system you can step through.
What it does
- Shows status. A two-line backlit display gives generator status, voltage, frequency, engine and battery information and run hours.
- Runs the exerciser. You set the day, the time and the type of exercise.
- Charges the battery. A built-in 2.5-amp charger keeps the starting battery ready.
- Reports faults in words. Warnings clear by themselves when the problem is fixed. Shutdowns need a reset.
- Tracks maintenance. A timer shows when the next service is due.
- Supports remote monitoring. Kohler’s OnCue system connects through the controller.
Power-up prompts
The manual notes a difference that owners should know. When the battery is connected, the RDC2 asks you to set the date, the time and the exerciser. The DC2 on the RESAL does not. So after a battery change on a 20RESA, expect the controller to ask for these, and set them. If you skip the exerciser, the controller will warn that no exercise is scheduled.
Exercise modes
- Unloaded cycle with complete system diagnostics. The default, and the one Kohler recommends. It runs 20 minutes: about 10 at reduced speed, 3 at full speed and 5 of cooldown.
- Unloaded full-speed exercise.
- Loaded full-speed exercise. The house is transferred to the generator. This mode needs an RXT transfer switch.
If utility power fails during an unloaded exercise, the manual says the switch transfers to the generator, the exercise ends and the controller stays in AUTO.
Clearing a fault on the RDC2
Find and fix the cause first. Then you can either press OFF, or use the menu: with the fault displayed, press Select to reach the overview, step to the fault, and change “Confirm Clear Fault” from NO to YES. Press AUTO to put the generator back on watch.
Resetting the maintenance timer on the RDC2
From the Overview menu, step down to the Genset Run Time menu. Press Select, step down to Next Maintenance, press Select, press the Up arrow until “Reset Maint Timer? Yes” shows, and press Select. After about two minutes the new interval and date appear.
Fuel Use and Gas Supply
Kohler’s spec sheet gives these figures for the 20 kW generator.
| Load | Natural gas | Propane vapor |
|---|---|---|
| Weekly exercise | 71 cubic feet per hour | 35 cubic feet per hour |
| 25% | 127 cubic feet per hour | 59 cubic feet per hour |
| 50% | 161 cubic feet per hour | 82 cubic feet per hour |
| 75% | 243 cubic feet per hour | 109 cubic feet per hour |
| 100% | 281 cubic feet per hour | 136 cubic feet per hour |
At half load on propane, 82 cubic feet of vapor an hour works out to about 2.3 gallons of liquid. A 500-gallon tank filled to the usual 80% holds about 400 gallons, which is roughly a week of nonstop half-load running.
On natural gas, the full-load demand is 281 cubic feet per hour, or about 281,000 Btu per hour. The spec sheet asks for a supply pressure of 5 to 11 inches of water column on natural gas and 7 to 11 inches on propane. Have a gas fitter confirm that your meter, regulator and pipe size can deliver that along with your other gas appliances. Our guide to Kohler natural gas home generators goes through meters and pipe sizes.
Maintenance in Brief
The 20 kW service schedule in Kohler’s manual is built around a yearly visit.
- Oil level: check every 8 hours of running, or before each use.
- Oil and oil filter: change every year or every 150 hours. Use 5W-30 or 10W-30 synthetic oil, and fill to the F mark on the dipstick.
- Oil cooler: clean every year or every 150 hours.
- Air cleaner and spark plugs: service at 150 and 300 hours. The plug gap is 0.030 inch.
- Battery: check the charger monthly, clean and tighten the terminals yearly.
- Fuel lines: inspect quarterly.
- Exercise: weekly, automatically.
- Dealer-only items: the brushes and collector ring every year or 300 hours, and the stepper motor coupling at 500 hours.
Before any work, disable the generator in the order the manual gives. Press OFF, disconnect the utility power to the generator, and remove the battery cables with the negative lead first. Our generator maintenance checklist covers the general routine.
Yearly service
Kohler Maintenance Kit for CH1000 Generators (17, 18 and 20 kW)
A genuine Kohler kit for generators with the CH1000 engine. Kohler’s listing says it includes the recommended air and oil filters and the correct amount of oil.
- FitsKohler CH1000 engine
- Generator sizes17, 18 and 20 kW
- IncludesAir filter, oil filter, oil
- BrandKohler
- UseRoutine yearly service
- Stock on listingIn stock when checked
- Why it works: the right filters and the right amount of oil arrive together.
- Who it is best for: 20RESA owners who service their own generator, and anyone preparing for storm season.
- What it solves: an oil change in the middle of a long outage, when 150 hours can pass in under a week.
- Keep in mind: check the engine model on your nameplate and the kit number in your manual before you order.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
Buying a Home With a 20RESA, or a Used One
A 20RESA already installed at a house you are buying is usually good news. The costly parts of any standby system, the gas line, the wiring, the switch and the permits, are done. Still, check it as you would a furnace or a roof.
- Read the run hours on the RDC2 display.
- Look for a fault message, and ask the seller about any past shutdowns.
- Ask for service records and the name of the dealer who maintains it.
- Check the age of the battery.
- Find the transfer switch and photograph its nameplate.
- Ask which circuits are backed up: the whole panel or selected circuits.
- Ask whether the generator runs on natural gas or propane, and who owns the propane tank.
- Look inside the enclosure for rodent nests, chewed wires and corrosion.
- Check that the area around the unit is clear and that it sits level.
- Ask for the installation permit and inspection record.
- Press RUN, with the seller’s agreement, and listen to it for a few minutes.
Buying a used 20RESA to move to another property is a different matter. The generator may be cheap, but installation is not. You still pay for a pad or base location, a gas line, a transfer switch, wiring, a permit and an inspection, and the unit has no warranty. Get an installer’s quote for the whole job before you buy the generator.
Keep It or Replace It?
- Keep it if it starts every week, has been serviced and still suits your loads. The CH1000 engine is still used in Kohler’s current 20 kW model, and service kits are sold.
- Repair it when the fault is a battery, a sensor or a routine part.
- Think about replacing it when a dealer quotes for a controller, an alternator or an engine, or when your home has outgrown 18 to 20 kW.
One point works in the 20RESA owner’s favor. Kohler’s spec sheet says the RXT transfer switch is designed for generators with the RDC2 or DC2 controller, and Kohler’s current air-cooled models use the RDC2. Ask your dealer whether your existing RXT switch can stay in place with a new generator. If it can, you may only need the generator.
Replacement Options
| Feature | Kohler 20RESA | Kohler 20RCA | Kohler 26RCA |
|---|---|---|---|
| Rating on LP | 20 kW | 20 kW | 26 kW |
| Rating on NG | 18 kW | 18 kW | 24 kW |
| Amps on LP | 83.3 | 83 | 109 |
| Engine | CH1000, 999 cc | CH1000, 999 cc | CH1006, 999 cc |
| Controller | RDC2 | RDC2 | RDC2 |
| Enclosure | Polymer | Aluminum | Aluminum |
| Sound, weekly exercise | 64 dB(A) | 64 dB(A) | 56 dB(A) |
| Sold with a switch? | No | No. The 20RCAL includes one | No. The 26RCAL includes one |
| Status | Discontinued | Current model | Current model |
Kohler has kept the same idea in its current range. The RCA models are generator-only, like the 20RESA. The RCAL models include a transfer switch, like the 20RESAL.
Current 20 kW package
Kohler 20RCAL-200SELS 20 kW Standby Generator with 200-Amp Transfer Switch
Today’s 20 kW Kohler with an RXT 200-amp, service-entrance rated automatic transfer switch in the box. It keeps the 20 kW and 18 kW ratings and the CH1000 engine family.
- Rating20 kW on LP, 18 kW on NG
- EngineKohler CH1000, 999 cc V-twin
- Transfer switchRXT 200-amp, service-entrance rated
- Sound64 dB(A) exercise, 69 dB(A) full speed
- Warranty on listing5-year limited
- Response time10 seconds
- Why it works: the same size and fuel demand as a 20RESA, so the existing gas line and location are a natural fit.
- Who it is best for: owners whose 20RESA needs a major repair and whose transfer switch is also due for renewal.
- What it solves: a new five-year warranty on both the generator and the switch in one order.
- Keep in mind: if your existing RXT switch can be reused, you may not need the bundled one. Installation is a separate cost, and stock was limited when we checked.
As an Amazon Associate we earn from qualifying purchases. Specs come from Kohler’s product page and the Amazon listing, checked October 2026.
Step up in size
Kohler 26RCAL-200SELS 26 kW Standby Generator with 200-Amp Transfer Switch
Kohler’s most powerful air-cooled home generator, sold with a 200-amp automatic transfer switch. It is also the quietest of the range during its weekly exercise.
- Rating26 kW on LP, 24 kW on NG
- EngineKohler CH1006, 999 cc V-twin
- Transfer switch200-amp automatic, included
- Sound56 dB(A) exercise, 67 dB(A) full speed
- Warranty on listing5 years
- Weight625 lb
- Why it works: 109 amps on propane gives real headroom on a 200-amp switch.
- Who it is best for: homes that have added a second air conditioner, a heat pump or an EV charger.
- What it solves: overload shutdowns on a whole-house switch, and a noisy weekly test.
- Keep in mind: it needs a larger gas supply and a 3/4 inch fuel inlet. Have the meter, regulator and pipe size checked before you order.
As an Amazon Associate we earn from qualifying purchases. Specs come from Kohler’s product page and the Amazon listing, checked October 2026.
Earlier-generation package
Kohler 20RESCL-200SELS 20 kW Standby Generator with 200-Amp Load-Shedding Transfer Switch
A complete package from the same generation as the 20RESA. The listing describes a 200-amp, service-entrance rated transfer switch with load shedding and a corrosion-proof enclosure.
- Rating20,000 W
- Transfer switch200-amp, service-entrance, load shedding
- Size48 x 26.2 x 29 inches
- BatteryGroup 51
- Weight500 lb
- Warranty on listing5 years or 2,000 hours
- Why it works: load shedding is built into the switch, which suits a 20 kW generator on a 200-amp service.
- Who it is best for: buyers who want this generation’s footprint and controls, for example to match an existing installation.
- What it solves: a like-for-like swap where the pad, clearances and gas line were laid out for this enclosure size.
- Keep in mind: this is an older model, and only a couple were in stock when we checked. Ask a Kohler dealer about parts support and warranty before choosing it over a current 20RCAL.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
For the full current range, see our guides to Kohler generators and Kohler generators for home use.
Common Mistakes With a 20RESA (and the Fix)
Pro Tips for 20RESA Owners
- Label the backed-up circuits. If your switch has a load center, mark which circuits are on it.
- Run a loaded exercise now and then, if you have an RXT switch. It proves the transfer, not just the engine.
- Keep the paperwork together. The generator manual, the switch manual, the permit and the service log belong in one folder.
- Reset the maintenance timer after each service.
- Ask about OnCue. Remote monitoring lets you see a fault when you are away from home.
- Recheck your loads after renovations. A new heat pump or EV charger changes the sums.
- Book service before storm season, not during it.
Real-Life Scenarios: Which Setup Fits?
These are typical situations. They are examples to help you decide, not reports from real customers.
🏡 The essential-circuits home
Your 20RESA feeds a 100-amp switch with a load center, covering the furnace, kitchen, well and a few rooms.
This is a relaxed setup with power to spare. Keep it serviced and enjoy it.
Verdict: leave it as it is
⚡ The whole-house switch that trips
Your 20RESA has a 200-amp switch, and it shuts down when the air conditioner and oven run together.
You are asking for more than 75 to 83 amps. Add load control, or move up in size.
Verdict: add load control
🏠 The house you are buying
The listing mentions a Kohler standby generator and nothing more.
Read the hours, photograph both nameplates, ask for records and have your inspector note the installation.
Verdict: verify before closing
Kohler 20RESA FAQ
What is the difference between the Kohler 20RESA and the 20RESAL?
They are the same 20 kW generator. The 20RESA was sold without a transfer switch and has the RDC2 controller. The 20RESAL was packaged with a 200-amp RXT transfer switch and has the DC2 controller.
What transfer switch does a Kohler 20RESA use?
It did not come with one, so it depends on the installation. Kohler's RXT switches, in 100, 200 and 400 amps and in standard or service-entrance versions, are designed to work with the RDC2 controller. Check the nameplate on your own switch.
How many amps does a Kohler 20RESA produce?
Kohler rates it at 83.3 amps on propane and 75 amps on natural gas, at 120/240 volts. The generator's line circuit breaker is 100 amps.
Can a Kohler 20RESA run a whole house?
It can run most of a typical home, including one central air conditioner. Homes with several large electric appliances need load control so they do not all run at once. On natural gas, plan around 18 kW.
What controller does the Kohler 20RESA have?
The Kohler RDC2. It has a two-line display and menus, runs the weekly exerciser, charges the battery and reports faults in words. When the battery is connected, it prompts for the date, time and exerciser.
What replaced the Kohler 20RESA?
The Kohler 20RCA, which is also sold without a transfer switch. It keeps the 20 kW propane and 18 kW natural gas ratings and the CH1000 engine. The 20RCAL is the version with a switch included.
Your Kohler 20RESA Checklist
- Photograph the nameplates on the generator and on the transfer switch.
- Note the switch’s amp rating and whether it is service-entrance rated.
- Find out which circuits are backed up.
- Know your fuel: 18 kW on natural gas, 20 kW on propane.
- Ask about load control if you have a whole-house switch.
- Keep the RDC2 in AUTO with the exerciser set.
- Set the date, time and exerciser after any battery change.
- Change the oil and filter every year or 150 hours.
- Book a dealer service once a year.
- Before any major repair, ask whether your switch can be reused with a new 20RCA.
The bottom line
The Kohler 20RESA is a strong 20 kW generator whose usefulness depends on the switch it was paired with. Know which switch you have, plan your loads around 75 to 83 amps, and keep the RDC2 set and serviced.
As an Amazon Associate we earn from qualifying purchases.
Sources: Kohler specification sheet G4-210 for the 14 kW and 20 kW RESAL generators; Kohler operation manual TP-6804 (6/15) for the 14/20RESA, 14/20RESAL and 20RESC/RESCL with RDC2 and DC2 controllers; Kohler’s automatic transfer switch pages and product pages for the 20RCA and 26RCA (kohlerhomeenergy.rehlko.com); Amazon listings for the Kohler CH1000 maintenance kit, 20RCAL-200SELS, 26RCAL-200SELS and 20RESCL-200SELS. All checked October 2026.
