Reducing Noise from an Oil-Fired Furnace

I was mulling your chimney over the other day and thinking of overall furnace design. It would interesting to make it lift off like many furnaces' lids - i.e. lever it up a couple inches then turn to left. Then lever the lid itself up a couple inches and turn to the right. It might make for a not very mobile furnace but you wouldn't need to lift the stack off either.

My other question - and forgive me if this has been addressed ready - do you think the chimney represents any back pressure on the flow of exhaust gases out of the furnace? Couple this potentially help hold more heat in or cause better combustion?

 

Jason,
I take the stack off to store it. That allows me to place a metal weather cover on the hot furnace. Using the cover is easier than welding a more permanent roof on the furnace lid and also allows easy access for any repair I might someday need to make to the dome lid. With the handle on the chimney and the turnbuckles on the guy wires, it is pretty easy to lift off the chimney and stow it.

I do use the lever lift and turn mechanism on my lid. Works well.

I sort of doubt the chimney causes much back pressure. Today I put it on with the furnace already burning and did not get the sense that the exhaust seemed to flow out around the chimney as I set it in place as you might expect were there much back pressure due to the chimney.

I don’t get the feeling the chimney has had a major impact on the furnace performance as I ran it a time or two chimneyless this Summer when the the neighbors were on vacation and did not see any noticeable performance difference. The negative impact it has is I can’t preheat feed stock on the vent like I used to, I can’t add metal through the chimney, and I can’t monitor the the fire directly though I am learning to monitor the chimney exhaust. That is different than looking into the furnace and seeing the condition of the metal and the flame color etc. But I am learning to live with it. I don’t hate it. I do like the quieting effect on the furnace.

Denis

 

I should have commented on the lifting handle arrangement on the chimney shown in pics in post 60 above. Having the lower handle oriented horizontally and the upper vertically and also near the balance point of the lower chimney section makes lifting it off much easier and controlled than if they were both oriented vertically. It is natural for the lower hand grabbing the horizontal handle to bear most of the weight and the upper to be guiding.

Once the section is cool---takes only a few minutes---carrying it back into the barn holding it only by the upper handle and down at your side is comfortable if the section balances at that upper handle. I also tuck the guy wires into the lower handle so they are aren't dragging and tangling.

Also the handles should stand away from the chimney enough to allow a welding-gloved hand into the handle with room to spare so you can lift it off hot without cooking the glove.

Denis

 

While I applaud your creativity, it's still easier to tell them, I'll see you in court! You have neighbors with nothing better to do with their lives than be a pain in your ass. NO ONE is that sensitive to a little noise a couple times a week for an hour or two. Time for you to take up skeet shooting! Love thy neighbor doesn't mean you have to like them and they don't have to like you.

I got nailed again recently in the land of the perpetually offended for a noise violation. (Longbeach) After 10pm they bust you if you break the limit. Last time I went in there I tip toed as quietly as possible, stayed high, with little power, no reverse and still bust it by 2 decibels. This time I went in there, flaps down, 400feet, slow as hell and FULL REVERSE on landing. YUP, still bust it by 2 decibels. It's funny to see that airport send a letter with 7bucks of postage with a dozen papers in it. No fine again, this time. If I was going in and out of that dump regularly, it would become a problem. There isn't a swinging soul that was alive BEFORE that airport was built. If you don't like airplane noise, don't live near an airport. This is not a hard concept.

 

"Swinging soul"



That's a new one, barely.

 

Frankfurt has a town noise limit just off the end of the runway, frightened the hell out of me when the pilot cut thrust moments after take off. Madness.

Silence was not 'golden' at that point.

 

Germany has some VERY heavy handed noise ordinances. 10pm and that was it. I forgot what it cost the air force to land a plane a ramstein after 10pm. Something like 500bucks. They made a buttload of money off us during the last war. We flew round the clock hauling crap for iraq.

 

My backside was making more noise than the engines at that point. I don't care how many times someone tells you it's normal procedure ........

 

Reducing noise is really tough. We build systems with regenerative blowers that are noisy. I reduced the noise quite a lot by buying a large diameter stainless pot to replace the intake filter cover and lined that with noise reduction foam from McMaster Carr. For blowers that are piped discharge most noise is from the intake.

That vertical pipe on the furnace can probably be ‘tuned’ by varying its length. A friend used to make a pipe gun that measured empty pipe lengths by the reflected wave that bounces back from the far end. It is called a standing wave and can have a big effect.

Sheet metal is particularly bad for low frequency noise. On machines I have built a tar mastic sheet glued to the inside makes a huge difference. I am building a CNC router to be used in a school and it will be fully enclosed with thin plywood covered with mastic sheet and layers of carpet.

 

Water also makes a really good noise isolator. Ran an f-16 one night in a hush house. Had some kind of water fall thing going on in the back. Only thing you heard outside was a low rumble. Back in the day, Spangdahlem had the first strike mission. (nukes) Some asshat serviced 6 of our jets with an engine oil cart that was loaded with hydraulic fluid. Never understood why they didn't notice it was blood red and not honey color. 3 of the airplanes actually flew! Those got motor changes that night. Your tax dollars at work.

 

Yes, when I started down the furnace muffler road I was prepared to have to hunt for the correct length (thinking of some sort of trombone slide arrangement!) of pipe so as to avoid resonant frequencies and anticipated a tedious bit of experimentation until I got it sorted. Needless to say I was really happy when I plopped on the 5 foot section of 10” pipe and could here a major decrease in noise and I was ecstatic when the added 4’ of 6” pipe knocked the noise down by a full 10 dB average. That proved to be enough so that at the property line I was measuring 4345 dB. Basically, I could just barely hear the furnace as distant traffic and the occasional bird calls were much louder.

That was enough to do what I needed. And, I can assure you, I had no interest in changing anything for fear of the system going out of tune. I think the Kaowool lining plays a major role in sound damping both because of its soft, thick, fibrous nature (acts somewhat like “acoustic” tiles) and its slightly corrugated surface. It also is the only reason the chimney doesn’t melt into a heap in 15 minutes run time. As it is, the lower section of chimney measures 500 deg F after 20 to 30 minutes burn time. Presently the noisiest part of my setup is the boxed-in acoustic tile-lined 24v DC leaf blower. The whole works—-combustion, leaf blower, fuel pump—-generates about 64 dB 4 feet from the furnace with the combustion causing a very muted gentle whooshing sound as best I can describe it. I should add that taking the pulsation out of my diaphragm-pump-pressurized (9 pounds) fuel line also took out a noticeable pulsation in the sound of combustion that was of the same frequency as the as the pump pulsation. That was done using an air-over-fuel accumulator pipe placed after the fuel pump in the fuel line connected to the Siphon nozzle.

BTW, I finished a 50 pound iron melt just an hour ago and remeasured sound levels which have remained constant.

I am sure there are more elegant fixes and that with some work could reduce sound emission even more. But, then, I’d rather melt iron.

Denis