Home/Retreat Power Generator Noise Reduction by "Jerry the Generator Guy"

Sunday, Nov 4, 2007

This article describes practical methods to eliminate four of the issues surrounding generators and their use.
Relatively common objections to home generators include; (1) They are often very noisy. This noise does/would bother both us and our neighbors.

(2) This high level of noise can serve as a “vermin attractor”. The vermin may need to be discouraged via your “biped eradicator”.

(3&4) Moving a generator inside a building will create both fire and exhaust hazards. I have read that after Hurricane Katrina there were several attempts to perform what we used to call “five finger discount” of someone’s generator. The following details some of the things that I have done at different locations to reduce or eliminate both the operational and security concerns.

Generator noise comes from 2 different aspects; (1). Mechanical noise from moving parts. (2). Combustion noise from the engine power. I have attacked each problem with
a separate approach. The exhaust is hazardous for two reasons. (1) It is hot. The hot surface can cause a fire if allowed to touch combustible items. (2) The exhaust contains both carbon monoxide and carbon dioxide. Both gases can be lethal if they not forced to leave the area where people or animals are found.

Solution # 1 - Mechanical Noise
I installed the generator into an insulated wood building. I used a shed / building size of 8 foot by 12 foot. This size [ < 100 square foot area ] is below the typical threshold where “approval” of the local planning and zoning [departments] is required. The walls and insulation serve as a noise barrier to contain the mechanical noise. There is a very real increase in mechanical noise when you enter this building. This noise cannot be heard above the ambient noise level when outside this building.

Solution #2 - Combustion Noise
The recessed immediate area around the exhaust port on most generator mufflers is typically about 1.75 inch diameter. Two inch automotive exhaust pipe is typically necked down [ reduced in diameter ] to approximately this size. This means a 2 inch exhaust pipe can be a reasonably snug fit if inserted into this space. This fit is not gas tight. I tightly wrapped the 2 inch pipe with high temperature Fiberglass insulation. This high temperature material is commonly used to wrap steam pipes. The wrapped pipe is inserted into a 3 inch type B double wall vent pipe. Type B vent pipe is what is used for exhaust of home furnaces and hot water heaters. The 3 inch vent pipe is mechanically centered into a 4 inch vent pipe. The 4 inch vent pipe is inserted into two "thimbles", one inside and one outside the building. The portion of the 4 inch pipe section, which is outside the building, has a perforated vent cover at the end of the vent pipe. A person walking by doesn’t see anything that indicates other than some natural/propane gas
fueled appliance is inside the building. The vent cover is removed and replaced by an automotive “turbo” [ low restriction ] muffler when “silent” running is desired. The muffler input 2 inch pipe is slipped onto the end of the 2 inch exhaust pipe.
The muffler end that is farthest from the building is supported on an H shaped construction of pipe. This muffler reduces the combustion noise to a very low level.

My wife has stated if you focus on listening that you can hear the generator running when inside the house if the vent pipe cover is used. The noise is reduced such that you have to get within approximately 20 feet before engine noise becomes noticeable when the muffler is installed. I have shown my noise reduction method to several neighbors. All very favorably commented that “Gee, you don’t even know it [the generator] is running until you got close to the building”.

Solution # 3 - Hot Exhaust

The half inch spacing gap between the 3 and 4 inch vent pipes allows some airflow to cool the piping. The use of the two thimbles, with appropriate wall cutbacks, holds the
vent / exhaust pipe assembly firmly in a fixed position. I measured the temperature of the exterior of the 4 inch pipe to be approximately 100 degrees F. above the ambient temperature. This multi layer approach reduces the risk of fire caused by overheating the wall to near zero, in my opinion.

Solution #4 - Hazardous CO Exhaust
Readers will recall a previous comment that the generator / pipe “attachment” is not gas tight. I has small amount of leakage of carbon monoxide (CO). This “looseness” means that some small amount
of exhaust can enter the building. My solution is as follows. I slightly pressurize the building by providing forced air via an 8 inch fan, [creating a "positive overpressure."] This fan is located inside a wall vent from the outside. This forced air has two benefits. It constantly supplies fresh cool combustion air to the generator. It also flushes any exhaust, or fumes from fuel storage/spills, via an exhaust vent to become diluted outside the building. The vents are located on opposite sides of the building to periodically cause an exchange of the total volume of the air inside the building.

JWR Adds: Anyone that has a portable (i.e. skid or cart mounted) generator that is not bolted down or locked in a generator shed with a sturdy door should consider securing it with a chain and padlock. You should preferably use a hardened bolt cutter-resistant resistant bike and motorcycle security chain and a large, stout, padlock that is warded to offer little room for bolt cutters to be used. Short lengths of specially hardened chain are available from BikeNashbar.com (item # OG-BC). Longer chains should be available from JCWhitney.com. There is an even larger selection of hardened motorcycle security chains is available in England--where in recent years nicking motorcycles seems to have become a national past-time.

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