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How to Make a Generator Exhaust Extension

The rule of thumb of operating a generator is, it must be run outdoors or in a place where the deadly carbon monoxide fumes can form. At times, this can be impossible or unachievable for some people for one reason or the other. The only option left is to extend their generator exhaust. So, how is it done?

It’s pretty simple; all you need is to make adjustments to a floor flange that will hold a 1.5-inch galvanized steel pipe of your desired length to the generator exhaust. It’d be best to use a gasket maker to seal the space between the flange and the exhaust to create a breakable seal.

It’s as easy as it sounds. You don’t need to weld anything, especially if you want a small exhaust extension, an improvement that cannot void your generator warranty. Continue reading to find out the steps to follow when carrying out this modification.

What’s the Easiest Way to Make an Exhaust Extension?

If you don’t have another option other than running your generator in the garage, shed, or RV camper, an exhaust extension provides a way to help ventilate exhaust fumes out. It’s an excellent way of ensuring you keep your family safe from the deadly carbon monoxide produced after fuel combustion.

So, how do you go about extending your generator exhaust without voiding the generator’s manufacturer warranty?

You can find all the parts you need to complete this DIY project on the shelves of your local hardware or automotive spare stores near you; you don’t need any fancy hardware. I should also mention; no welding is required.

Parts, Tools, and Equipment Needed

1 inch round threaded floor flange
1.5-inch flexible exhaust repair kit
High-Temperature RTV Silicone Gasket Maker
1-inch by 3-inch Threaded Nipple
Longer Mounting Bolt

Steps to Follow

Tip: If you are extending the inverter generator’s exhaust, it’d be best to remove the rear cover to expose the exhaust system.

Step 1: Remove the Flange holding the Spark Arrestor

If your generator has a flange holding the spark arrestor to the exhaust system, remove it and use it to make adjustments to your floor flange, which you’ll replace it with. A floor flange is thick enough to support the extra weight added by the new extension. It will also prevent the need for welding.

Step 2: Mark Out the Size of Flange Needed

Using the manufacturer’s exhaust arrestor bracket, mark out the holes on the new floor flange and the shape of the custom flange to use. It will give you an idea of where to drill the mounting holes and cut the new flange to fit the pre-existing exhaust.

Sketch out your desired shape using a marker pen, as you’ll probably need to cut some matter out. While marking the flange, make sure you’ve enough material for the mounting and enough contact surface with the existing muffler to offer the necessary seal between the two surfaces.

Suppose your unit is an enclosed inverter generator. In that case, you want to make sure the pre-existing piping is dead center to avoid the new exhaust extension from coming into contact with the shroud cover as it could potentially cause melting.

Step 3: Cut Out the Extra Matter on the Floor Flange

Before starting the cutting, wear the necessary protective eyewear and gloves. Cutting metal causes friction that creates hot surfaces capable of causing burns. What’s more, there is a small metal fragment that will fly all-around when you start cutting.

Using a vice to hold the floor flange firmly, take your grinder with a cutoff wheel and carefully cut out the extra galvanized steel material, shaping it to fit onto the muffler.

Take your time here to achieve your desired shape. The grinder should make the cutting and shaping work rather easy. Don’t be in a hurry; allow the grinder to do its job. It’d probably take you over 15 minutes, which is okay.

Cutting the material can be tricky; try and cut the material in straight lines to avoid binding between the cutoffs as that could cause kickback or even break your grinder wheel. It’s not a must you make it pretty; create something practical.

Step 4: Drill the Screw/Bolt Holes

With the cutting done, it’s time to drill the screw or bolt holes on the spots you marked earlier. Trace out the hole you need and use the correct size bit to drill the holes out.

And since the material can be pretty tough to drill, allow the drill to do its work; don’t force it. Also, apply some cutting lubrication fluid on the spot as you drill to avoid breaking or accelerating wear and tear on your drill bits.

After drilling the holes, you can use a pointy stone bit to add bevel edges to the screw holes to give the screw some extra wiggle room to give them fine adjustment, though not that important.

Step 5: Lay Some Painters Tape

Next is to lay some blue painter’s tape on the exhaust muffler before adding the gasket maker to keep it on the flange only and not on the muffler surface.

Step 6: Apply Some Gasket Maker

Since the muffler attachment point and the flange surface aren’t genuinely flat to create a flash, a gasket is necessary to create a complete seal. The RTV Silicone Gasket Maker will help you make a high-temperature-resistant gasket.

Using a marker, trace out the flange pattern on the painter’s tape so you can know the boundary where to apply the RTV Silicone Gasket Maker. If there is a pre-existing exhaust pipe, stick some blue painters on it too.

Don’t forget to cut away the tape covering the screw holes, as leaving it on could prevent the screws from holding in when tightening the flange.

In some generators, you might need to flip the unit to have better access to the muffler when and easy time applying the gasket maker paste. Before flipping it, make sure you drain the oil to prevent messing with your workshop and causing the oil to reach areas in the generator where it shouldn’t.

Now that you’ve marked the area, apply enough RTV Silicone Gasket Maker on the traced patterns. Try to avoid the screw holes but don’t leave a gap.

When applying the gasket maker to the pre-existing pipe, go as high as half its length. Make sure no silicon enters the tubing. Once you’re done, place the flange on it and screw in the bolts without tightening them.

Smoothen any extra silicone around the customized flange with your finger and flat it out, making sure you pressed it tightly against the flange sidewalls.

If there is extra silicone in the flange’s threaded area, something unavoidable, do not worry. Use a paper towel to wipe it out.

That allows you to ensure a tight seal between these surfaces to ensure the hot exhaust gases escape through the threaded area.

Step 7: Give the Gasket Maker Time to Cure

Allow the gasket maker to cure as directed in the manufacturer’s manual before you can tighten the flange screw or bolts, around 1-hour. Come back, tighten the bolts, and allow the silicone to cure as directed in the user’s manual, generally for 24 hours.

Step 8: Cut Out the Excess Gasket

With the gasket maker cured, you can now remove the mounting bolts and free the flange with the new gasket. Remove the painter’s tape and set the flange in place to ensure a tight seal.

Remove the flange and set it on the table. Cut out the excess gasket flashing to give it a professional look.

If you see an area that isn’t covered or broke away a section during the cleanup, apply some of the RTV gasket makers, smoothen it out and allow it to cure.

Step 9: Tighten the Flange to the Muffler

With the flange and gasket ready, connect them to the muffler and tighten the screws or bolts to make sure it creates a tight seal. Make sure to use the longer screws you purchased; their extra length caters to the additional material added by the new flange.

Step 10: Mount the Threaded Nipple to the Flange

Connect the threaded hose nipple to the flange and tighten it. You want to make sure it gets enough contact with the flange to create a seal and prevent it from shaking from all the generator vibrations when operating.

Step 11: Attach the Flexible Steel Tubing

Take the galvanized flex tubing and attach it to the steel nipple you mounted to the flange in the previous step.

Apply some RVT silicone to the contact space between the nipple and the tube to create a seal. Smoothen the silicone out using a paper towel to give it a nice flush.

Use the U-bolt clamp to tighten the joint to make sure it never breaks free.

Tip: if you are working on an inverter generator with a rear cover, install it before connecting the flex galvanized steel hose.

Step 12: Test Your Exhaust Extension

Even if you were extra careful when installing the new exhaust extension, an error could have occurred without you knowing. The flex tube might have been damaged, or the clamp loosened. Whatever the case, a test run wouldn’t hurt.

Take your generator outside, start its engine and leave it to run for 5-10 minutes. While it’s running, observe all your extension connections to make sure things are working correctly.

If everything works right, you’re in luck, and your extension is ready for practical application.

Is it Safe to Run a Generator with an Exhaust Extension Indoors?

No! Running a generator indoors is never safe. Allot can go wrong, including carbon monoxide poisoning that kills people.

You can only go for this option if there’s absolutely no other way to run the generator outdoors. However, it’d be best to ensure it’s a cool and dry place with enough ventilation.

Also, consider installing a CO detector alarm to warn you when there are dangerous levels of carbon monoxide. Before starting the generator, make sure the device works properly.

About the author

Sharif Gen

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