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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14988
Experience:  Certified on Onan and Generac generators
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I want to convert my gasoline powered Generac Guardian 15KW

Resolved Question:

I want to convert my gasoline powered Generac Guardian 15KW Ultra Source generator to also use propane or natural gas fuel. Does Generac sell the conversion kit, or where is the best place to get it, what does it cost, and what additionally do I need (if anything) besides the kit? Please give details, options and advice.
Submitted: 6 years ago.
Category: Small Engine
Expert:  Hank F. replied 6 years ago.

Thank you for choosing Just Answer for the solution to your problem.
My name is XXXXX XXXXX I am going to assist you with this.


I do not know if Generac offers this conversion or not - I have never checked.


But I do know this place offers it, and is where I would get it from.

These people specialize in nothing but conversion kits.


The cost depends on which way you want to go with it.


Customer: replied 6 years ago.
Relist: Other.
I already know everything your "expert" related. I'm looking for complete details with options and advice on which option is best to choose and why.
Expert:  Hank F. replied 6 years ago.

There is no "best" option - every users needs and situation are unique.


Your choices are:

1. Leave the genset to run on gasoline only.

2. Convert the genset to run on gasoline or high pressure LP.

3. Convert the genset to run on gasoline or low pressure LP or NG.


Portable gensets most often run on gasoline, due to the fact that when you move it around, the fuel source stays with the genset. No special accommodations must be made for gasoline, like they do with LP or NG.


Home standby sets are most often LP or NG, due to the fact that the gasoline goes bad very quickly - in as little as 30 days. LP and NG do not go bad. Also, no special provisions must be made to alternate fuel sources.


When using a gasoline set, special care must be given to run the set at regular intervals, and the use of fuel stabilizers is an absolute must. Fuel stabilizers will not stop the decay of gasoline - they only slow it down. Eventually, the carburetor will need to be cleaned/repaired.


LP or NG? This is a question that creates great debate.

The advantages to LP are:

1. LP is considered 'portable'. You can carry tanks of LP with you, although it is not as convenient as gasoline.

2. LP is slightly more efficient than NG. An engine will produce slightly more power on LP than it will on the same volume of NG. However, this difference is very slight - the difference can only be seen in very long term tests, with special equipment.



The advantages to NG are:

1. NG is typically a bit cheaper than LP. Believe it or not, but one of the components of LP is NG!

2. With NG, you never have to worry about calling the refueling truck, like you do with LP.


Both LP and NG are much cleaner burning than gasoline - both have greatly reduced emissions than gasoline.

However, one drawback to using either LP or NG is the fact that engines do not tend to last as long. This is due to the fact that LP and NG engines run at slightly hotter temperatures than a gasoline engine. In a gasoline engine, the incoming fuel helps to reduce the cylinder temperature slightly.



High pressure or low pressure applications? Again, this is another 50-50 debate.

Without going in to the complete physics of LP use, you need to understand this:

LP is technically a gaseous fuel - even though it is stored in liquid form. LP vapor is compressed 270 times to convert it to liquid form. Stored as a liquid, you can get 270 times as much fuel in a given container than if it were stored in vapor form.

An engine does not actually burn the liquid - instead, it is converted to vapor and then used by the engine.

On a high pressure application, this vapor conversion (called vaporization), occurs at the genset itself. All piping to the genset contains liquid propane.

On a low pressure application, vaporization occurs at the primary regulator, usually mounted at the tank itself. Therefore, all piping to the genset only contains vapor.


I personally do not like high pressure systems - although safe when properly maintained, they are very dangerous to work on..

First is the pressure itself. LP is extremely temperature dependent - the higher the temperature, the higher the pressure. On average, the pressure of liquid propane at 70 degrees F is about 125 psi. At 100 degrees F, this pressure jumps to about 200 psi.

Second is the operating temperature. LP vaporizes at -44 degrees F. When the liquid boils into a vapor, the temperature of the liquid is actually NEGATIVE 44 degrees! Coming in contact with liquid propane can freeze your skin in seconds.

A low pressure system operates on less than 1 psi.


Also consider the leak factor. Although the fuel system is very safe, damage is always a possibility. All LP systems use a safety device called a free flow preventer (typically built in to the regulator and/or fittings). If functioning properly, this device will automatically shut off the flow of propane if it senses a free flow situation (too much fuel flowing), as in a severed line.

But suppose a line gets just a pin hole in it, enough to cause a leak, but not enough to trip the FFP?

With the low pressure system, the fuel is going to leak very slowly.

But even though the high pressure system will also leak slowly, you are losing 270 times as much fuel (remember it is compressed 270 times to convert it to liquid).

If a leak were to develop on a high pressure system, and you lose say, 1 gallon of fuel, once it vaporizes, you now have 270 gallons of vapor.

Which would have a higher chance of finding an ignition source, 1 gallon of vapor or 270 gallons of vapor?



These are the explanations. Now, on to your situation.


If this set is going to be used primarily as emergency backup, I would highly recommend the low pressure conversion. Running on LP or NG is technically a moot point, and is up to your personal preferences. Availability of NG is your biggest factor. Another consideration that must be factored in is what your local code says about capping a fuel line when an appliance is removed. What needs to be done if you pull the set and use it in a remote location?


If this set is going to be used primarily as a portable, I would recommend leaving it as gasoline only. Once you have put any gasoline in it, even once, the carb is subject to formation build up from the degradation of gasoline. And 'running an engine out of gas' is not an option. Even though it may use up enough gas to where the engine can no longer run, there is still gas left in the carb - and it WILL go bad and cause problems.



The kits I mentioned in my last post contain everything to convert the engine to an alternate fuel source. The only other thing you would be responsible for is getting the fuel to the genset.

With NG, this would mean a tie in to your existing NG system - in accordance with your local codes and protocols.

With an LP system, this would mean getting an appropriate size tank (if you do not already have one), primary regulator and piping - again, in accordance with code.



Their high pressure conversion kit (Type 2) runs $357 for your set.

The low pressure kit (Type 4) runs $397.



Edited by Hank F. on 1/16/2011 at 4:37 PM EST
Customer: replied 6 years ago.
Excellent! Now that's the kind of answer I was looking for. You also solved my carb puzzle. I made sure the engine ran out of gas between runs, but now I see that some gas remained in the carb which is why it's gummed up. Where do I get a good carburetor cleaning kit for small engine carbs?
Expert:  Hank F. replied 6 years ago.

There is no cleaning kit.

These newer engines use EPA compliant carbs, and per EPA rules, a carb is not supposed to be repaired - only replaced.


The only way to truly clean a carb is to remove it, disassemble it, and soak it in a commercial carburetor solvent, such as that available at NAPA or an auto parts store.

For best results, allow it to soak overnight.

Then clean it well with a spray type cleaner to remove all solvent, and allow it to thoroughly dry, either naturally or with compressed air.


Be very careful not to break or lose any parts, as there are no replaceable parts.


If a good cleaning still does not help, the carb will need to be replaced.


Edited by Hank F. on 1/16/2011 at 8:02 PM EST
Hank F. and 2 other Small Engine Specialists are ready to help you
Expert:  Hank F. replied 6 years ago.

Did you get my last post?