How to Make a Generator Quiet

Before you begin to soundproof a generator you will need to answer a few basic questions. Once you know what you want to accomplish, there is a much better chance of achieving your goal. ‘Ready, shoot, aim’ very rarely works best.

What do you need to accomplish? And why?

What am I using my generator for?

Most of us have reached the point in our lives that we do not even think about life without electricity. It is just there. Walk into a room, flick a switch, and the light goes on. Grab a couple ice cubes to cool a drink. Sit in front of your computer and Google ‘Soundproofing your Generator’. A catastrophe is forgetting to plug in your cell phone.

Consider your life without power for 3 days–72 hours. Does the temperature reach 100 degrees or -40 degrees? Being without power in either situation is annoying at best–life-threatening at worst. Based on those criteria, here are my top 5 reasons for having a portable generator.

  1. Emergency Power – For the most important things in your house like heating and cooling, light and water, and, of course, your computer and phone.
  2. Natural Disaster – Kind of the same as Emergency Power. The biggest difference is you may need power to help someone else instead of dealing with your own power outage. (I have discovered that electric chain saws work better when plugged in.)
  3. Jobsites – Every type of nailing, stapling, and cutting works better with power.
  4. Camping – In my misspent youth, camping involved Coleman stoves and lanterns, a big fire, and beer. Now it involves all things electrical–and beer.
  5. Outdoor Events – Kind of like camping but with different purposes such as weddings, outdoor parties, farm markets, small concerts.

How much power do I need?

The answer to this question depends on your priorities. And your faith in an electrical grid run by people you do not know. It ranges from ‘complete faith’ to ‘the end is near’. The only ‘complete faith’ I have is in Murphy’s Law–‘If it can go wrong, it will.’ And most of the time I suspect that Murphy was an optimist. Therefore, we have a 9000 watt generator that will run everything we want in the house from the 12 volt furnace igniter to the electric clothes dryer (not all at the same time). You may not need, or want, that much capacity–or to spend that much money–but if you are replacing your generator, or buying one for the first time, make sure you consider all of the different uses for it. Then add a little more.

  1. Emergency Power – Anything, and everything you consider essential. Refrigerator, microwave, some lights, air conditioner, cell phone charger, and ????
  2. Natural Disaster – Hard to plan for, but you do know your living environment, and what may happen. Lights, phone charger, air pump, saw, and ????
  3. Jobsites – Depends whether you are leisurely building a deck at your cabin, or you are a professional contractor with compressors, saws, and radios all running at the same time.
  4. Camping – Depends on how much convenience you expect, but a 2ooo watt generator should be more than sufficient.
  5. Outdoor Events – Are you powering a small wedding or a Rolling Stones stage show? Power requirements are vastly different.

How quiet do I need to make it?

Quiet enough so your neighbor does not come over and treat you like Senator Rand Paul. Seriously, as quiet as possible. 50 – 52 decibels seems to be the goal to strive for. A Purdue University chart describes 50 db as a quiet suburb or conversation in a quiet house. 50 db has also been compared to a refrigerator, an electric fan, and a hairdryer.

If you plan to buy a new generator it is best to start with one that is as quiet as possible–then make it quieter. The Champion 4000 Watt unit only produces 64 decibels but with a little selective use, it will probably do well as a home backup. By adding a muffler and putting it in a quiet box you should be happy with the result of your soundproofing.

 

How to make your home emergency generator quiet

If your generator is meant only as back-up emergency power for your house, location is the most important consideration for your soundproofing efforts. A generator that has to be moved close to the house or garage, then plugged in, will likely be sitting in the open, and will need some kind of soundproofing. If it lives in the garage, or a dedicated structure, you will need a different plan.

How to build a generator quiet box — once

Full disclosure. I have never built one of these–because I never had to. When we built our house I trenched a 100 amp electrical service into the garage. Our 9000 watt generator sits in the corner under the breaker box, is vented through the wall, and hooked up to the breaker box with a transfer switch.

The system was installed to code and certified by a journeyman electrician. (I can live in peace with my wife, and my insurance company.) I just turn things off and on according to his instructions and start up the generator. It never moves and is very quiet out there. If you are building new, or adding a garage, or upgrading your electrical you should certainly consider this option.

Having said all that, here is the plan I would use to build a quiet box. First, a few caveats:

  • MDF (Medium Density Fiberboard) – Great for soundproofing but it absorbs moisture and swells, does not hold screws, or nails, or glue, as well as plywood, and it is way heavier than plywood. I have no intention of building a box with it. There are enough light, thin, and better soundproofing products available that the possible additional quiet of MDF is not worth the drawbacks.
  • Build a complete box–bottom and all – If you are taking it camping, or moving it into position for emergency power, why pack, or move, the generator and the quiet box separately when the ultimate plan is to have one inside the other anyway.
  • No tool list – If you are going to take this on, I assume that you have the necessary tools; or know what you need. 
  • No material amounts – The size of your generator determines the amount of materials you will need. I see no practical use in giving you the amounts of material I need for my generator if yours is half the size. The type of materials, and how to use them, is more important.

Materials

  • 1/2″ G1S (Good One Side) plywood
  • Miscellaneous dimensional lumber
  • MLV (Mass Loaded Vinyl) sheet
  • Heat or flame resistant soundproofing material
  • Green glue
  • Adhesive and Acoustic caulking
  • Fasteners – Various lengths and types of screws
  • Handles and latches
  • Piano hinge
  • Vents
  • Wheels
  • Exterior paint and primer

You will need to make the sides, ends, top, and bottom about 2 inches bigger than the generator–in every direction–to give yourself room for reinforcing corners, and exhaust piping. Construct all 6 sections of the box as a sandwich panel–G1S plywood, Green Glue, MLV, Green Glue, G1S Plywood (make sure the good side of the plywood faces out). Screw your sandwich together with 1 inch countersunk deck screws from what will be the outside of the box.

Note: I would build the panels with uncut 4 x 8 plywood sheets first–then cut out my sections. That way I ensure the MLV and Green Glue extend to all of the edges. Just make sure you lay out the sizes on the plywood first to get the best use of your product. It will also keep you from putting screws where your saw blade is going to be cutting. Remember Murphy’s Law.

Attach the walls to the bottom by setting them on top. That way your lid will be the correct size. Glued and screwed! (It is something I live by. In my opinion–most things cannot be made too solid.) Make sure it is square.

Caulk all of the joints with acoustic caulking, then install non-flammable self-sticking sound deadening insulation to the insides of all surfaces.

Cut 2 x 2 to the proper lengths and install them on all of the inside joints with 2 1/2″ deck screws. Three or four screws from each side. (Unfortunately you will not be able to glue these pieces because they are installed over insulation. In this case the soundproofing is more important.) The 2 x 2 will provide a solid base when you attach wheels.

Install a 2 x 2 horizontally across the middle of each end section (for handles) and around the inside perimeter of the top of the walls to support your lid.

Now, after all of that careful soundproofing, you need to cut holes in the box. One for exhaust pipe and one or two for air intake and cooling. I do not know the size of your exhaust pipe so you will have to decide on the size of hole for the pipe extension. Just make sure that you cut it big enough to accept the pipe and a fire sleeve. (Setting your quiet box on fire is a bad option.)

To cut down exhaust noise even further add a flex tube to the extension. You can run it 20 feet further away, bend it upwards, or put the end in a pail of water to deaden the sound. (Make sure the pail is below the level of the generator to keep water from backing up into the pipe.)

You can also attach a muffler (or silencer) to the end of the short pipe or the extension (although there is some disagreement about the value of a muffler).

For air intake and cooling I would buy two 4″ vents. Install one in the end of the box opposite the exhaust as an intake. The second one I would not install until I had run the generator for at least a couple of hours to see how hot it gets in the box. If it is too hot, install the other vent in the lid. If you have hole saws, or want to buy a couple, use them for the exhaust and vent holes. You can mark them out and cut them with a jig saw but the hole saw makes a much cleaner job. Get a low-profile vent with a screen.

Once your vents and exhaust pipe are installed, fill any gap between them and the surrounding wood with good caulking. Do not use acoustic caulking because it never drys and will attract dirt. Caulk inside and outside. Now you will need to drill one more hole to install a transfer kit which will get the power to the outside of the box. I could never understand the idea of building a quiet box–then opening the lid to plug things into the unit. With the transfer kit you have 6 outlets on the outside of the box. The only drawback is that they are not waterproof. In which case I would get a SOCKiT Box and modify it to waterproof my plugs.

Install handles on each end. They will need to be positioned where you installed the extra horizontal 2 x 2 to ensure that you can lift the box without ripping them out. Depending on the size of your generator, you may never want to lift it–and may never have to–but having handles, if it becomes necessary, does not hurt. Fold down handles will have the lowest profile. 

Turn the box upside down and install four locking wheels on the corners. I want 5″ wheels with good locks. Very rarely–specially when camping–will your generator be sitting perfectly level and locking the wheels will save you from chasing it around. The bigger wheels will make it way easier to move around. You will probably have to get longer bolts. You want to bolt it through the 2 x 2 and through the box. You will need 4 inch bolts c/w washers and nuts for that.

You will want to secure the compressor in the box. If you are certain that the box will never be on a steep incline, or fall over, or you will never drive over washboard road and potholes, you can probably just screw some blocking inside on the base to keep it from moving around.

If it moves too much you will–at the very least–have a problem with your exhaust extension. It could be much worse. You can make it semi-permanent by using U-bolts to attach the frame to base of the box. Mark the location of 4 U-bolts, drill through the base, and tighten them down. Yes, there is a little noise transference, but it is better than the big noise of your generator banging around in the box.

Now, install the lid. You already made it when you made the sides and bottom. Cut your piano hinge to fit a long side and attach it to the lid. Then attach lid to the box. If you want a better seal than the one provided by the insulation add 1″ wide self-sticking weatherstrip to the top edges of the box. Attaching a light chain like a bird feeder chain to the inside of the box and inside of the lid will prevent it from opening too far and ripping off the piano hinge. Install a couple of eye hooks or a hasp latch to keep the lid tight. A good quality primer and two coats of exterior paint and you should be ready to go.

Notes

  • No, I did not forget that you need to change the oil occasionally. I even gave some thought to designing the box with an oil change trap door in the bottom. (Seemed a little too anal–even for me.) And unless you are running it constantly you only need to deal with one oil change every spring. When you lift it out of the box to change oil, you also have the opportunity to inspect the soundproofing material and exhaust extension, oil the hinges, and clean the generator.

Make a generator quiet space in your garage

If your generator is a permanent fixture in your garage with a transfer switch arrangement for back-up power–or even if you just run extension cords as needed–you can still soundproof that small area without having to consider the whole garage. Essentially, you are going to construct a soundproof box in your garage. I would choose a corner location, if possible, because then I would only have to build 2 walls and a roof, and extending the exhaust outside is convenient. 

First, insulate the exterior walls with Roxul 80 soundproof insulation at least one foot higher than your intended top of the box. Install a double layer of 1/2″ drywall to the same height as the Roxul with Green Glue between the layers. Now construct a lid, one end wall, and a door using the same method as described above in the ‘How to Build a Generator Quiet Box’.

Securely attach a 2 x 4 ledger board over the drywall. Make sure that you double screw it into the studs (because you know you will be piling things on the lid almost before it is finished). Set the lid on the ledger and screw it down. Position the end wall under the lid and screw it in place. Attach a 2 x 2 vertically in the corner where the end wall meets the drywall for backing. It is best if the 2 x 2 can be screwed to a wall stud or wood backing you installed before the drywall.

Now for the door. Hanging it with a piano hinge on the exterior wall is the best choice. Just keep in mind that it will have to be at least 1 1/4″ from the wall to allow it to open fully. So install a double 2 x 4 vertically to give you the backing you need. Give some consideration to installing a small castor on the bottom of the latch side of the door so it rolls on the floor instead of dragging on concrete. 

Everything else is pretty much the same as building the box above. You will need to  drill a hole to exhaust it outside (remember a fire sleeve), drill at least one air intake with a vent, non-flammable, self-sticking sound deadening insulation on all interior surfaces, acoustic caulking on all joints, a handle, and latches. Get an exercise equipment floor matto set the generator on, hook it up, and use as required.

Note: If you are absolutely certain that this is a permanent location for your generator, then make sure you glue all of the wall sections and wood backing in place. You may not want to dance on the lid but storing things with weight up there should be an option. 

If you have the generator in a sound-proof box already, then your only consideration is the exhaust which can be as simple as a flexible exhaust pipe you run out of a door, window, or dedicated hole you have in the wall whenever you need the generator. Having a longer pipe–most of which is in the garage–with a couple of direction changes will eliminate almost all of the sound outside.

Soundproofing a dedicated generator shed

If you live in a location where power outages are common and/or long-lasting (such as serious winter or summer storm areas), it may be beneficial to house your emergency generator in a dedicated building close to the house, greenhouse, milking parlor, or wherever your need for power is most important. Essentially, you are going to construct, or buy, a small garden shed.

Use Roxul 80 soundproofing batts in the walls and ceiling, then double drywall with Green Gluesandwiched between the layers, and an exercise floor mat for the generator to sit on.

Make sure that the door has weatherstrip and non-flammable self-sticking sound-deadening insulation on the inside. Extend the exhaust through the wall with the pipe pointed vertically.

Make sure any exhaust pipe passing through flammable material is inside a fire sleeve. If your shed is really airtight, and the generator will run for hours non-stop, you should also install a 4″ air intake vent.

You will want to make your generator shed as quiet as possible if it is close to the house. If you are using it more than 3 or 4 times a year because of power failures, give some consideration to attaching the shed to the house where it will be plugged in. Make sure that you get the house wall well soundproofed also to prevent both Airborne and Impact noise from entering the house.

Warm and asleep is way better than warm and awake. Having the generator right where you need it in an emergency situation sure beats dragging something weighing 250 lb through the snow, or mud, or wind. You can always take it out of the shed if necessary to use in another location.

How to soundproof a portable generator

If you go camping with a portable generator, making it quiet will be very important to both you, and your neighbors. If you use a generator on a job site, the location, and noise tolerance of both you and your customers, will dictate the amount of soundproofing required.

Soundproofing your old portable generator

If you do not want to invest the money in a new portable generator, but still want the security of using your old one quietly, your best bet is to build the quiet box described above. Other options include shielding it with almost anything that will cut down the noise–even leaning plywood on each side of it will force sound up instead of outwards into the surrounding area. Adding an exhaust pipe extension that points vertically instead of horizontally will also cut down the noise. 

Most conventional generators have to run at 3600 rpm to develop the required power. Inverter generators can run at variable speed because of their design. 

Buy a quiet inverter generator-and make it quieter

On the other hand, if you are in the market for a new generator, or want to replace the one you have, you might want to consider an inverter generator. They are very quiet compared to a conventional generator. The decibel level can be as low as 47 when idling–up to about 58. You can quiet them even more just by surrounding them with almost anything you have around the house or campsite; even throwing a blanket over them will help a lot. They provide more consistent power and usually are designed to power up or down as demand increases or decreases. Depending on the size they can easily power your refrigerator and some lights. But about the most power you can get from them is around 4000 watts.

You can purchase a conventional generator that produces well in excess of 10,000 watts. I do not think that one type is any better than the other. You need to assess your requirements–including how much power you need, and for what. Will you want to move it often? Or will it stay in one place? How quiet does it have to be?

Because the best generator for you depends on what you plan to use it for. For a useful comparison of inverter generators and conventional generators, you might want to check out https://www.norwall.com/power-expert/generators-and-inverters-whats-the-difference. Their blog provides a lot of useful information that should help you make your decision. 

 

Why you should have a soundproof generator, final thoughts

I firmly believe that everyone should have a generator–given the world we are living in. Even if it is only a small solar powered unit that provides light and makes coffee. Living on the 32nd floor of a high-rise apartment building without power of any kind for 3 or 4 days could be annoying. I have never tried it–and do not intend to–so I may be wrong.

On the other hand, living in a house without power for 3 or 4 days at minus 20 could also test your patience. The ability to have light, stay warm, and save your food–quietly–is a comforting feeling if you are worried about the power grid.

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Terry Schutz
I have worked as a contractor, sales person, and business owner in the construction industry for over three decades--mostly in home renovations and also as a home builder. I have been married to the same wife for 46 years. We have 3 children and 4 granddaughters. I have also been writing semi-professionally for about 20 years--construction articles, personal stories, and politically incorrect social commentary.

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