DIY Muffler for Diesel Heater

When I installed a diesel heater on my boat, I was concerned about the exhaust noise.  I had tried the muffler that came with the heater, but it was a fail for two reasons.  1) It was spot welded around the edges and therefore was not possible to use aboard.  It would leak exhaust fumes inside.  2) It barely worked.  There are two versions of the little stainless muffler that comes with these diesel heaters, although they look identical on the outside.  One is a straight-through design and the other has a little bend.  They are a "glass pack" style of muffler with the exhaust pipe, having perforations, going though a canister filled with spun fiberglass.  But they are tiny and barely take the edge off of the whining exhaust note.

I decided to build my own.  The flexible stainless steel exhaust pipe that came with my heater was about 23mm.  That slipped over standard copper 3/4" pipe in my scrap pile.  I also had a few feet of 1.5" copper pipe.  I bought a couple end caps for the 1.5" pipe and went about building my muffler.  I drilled a bunch of little holes (1/8") in the center section of the 3/4" copper pipe.  I then drilled holes in the ends of the 1.5" end caps to fit the O.D. of the 3/4" pipe.  I soldered one end cap on the 1.5" pipe, slipped the 3/4" pipe through, filled the 1.5" pipe with spun fiberglass (from my attic insulation), put it all together and soldered it up (high-temp solder).

Here it is next to the stainless muffler that came with my diesel heater.

On the right is a 3/4" elbow and then a little length of the flexible stainless exhaust tubing that came with the heater. It is sealed with a hose clamp and high temp silicon.  I also attached a little of the stainless exhaust tubing on the other end (which then attaches to the through-hull) to make alignment easy.

Since my fabricated muffler is 4 times longer than the stainless muffler, I was expecting an improvement.  But it was even better than expected.  A neighbor in the marina asked how my diesel heater project was going and I told him that it was running as we were talking.  But it can't be heard.  I decided to make a video/sound recording.  To actually hear it, I had to climb on the boat next to me and hold my phone down by the exhaust outlet.  Even then, I had to turn up the microphone sensitivity.  Unfortunately, every time I recorded, some gulls started screaming a few docks away.  But it is possible to hear the heater if one were in a dinghy passing by a few feet away.

Here is another recording that I made at a really quiet anchorage in northwest British Columbia.  I stuck the phone out the window right above the diesel heater exhaust.  Dang it, again the background noise covered up the sound of the heater exhaust.