Kerosene and flare fittings

[pavo6503]

Did a call at a home today. The owner said there was fuel leaking from the fuel lines near the burner. Obviously that's dangerous so I was sent right over.

Everything looked brand new. New fuel lines, new shutoff valves, new filter can etc.

The furnace was in the basement, the old one had originally been inside the house. I found a few very slow leaks, very very slow. A drop would form maybe every 5 minutes or so on the bottom of the shutoffs and around the gasket on the filter. I took apart the offending flare joints and it looks like the guy who did the install did a good job. No splits, cuts, burrs or any of that. When I put the flares back together I put a little pro-dope on them since I couldn't think of anything better to do besides tighten them down as best as I could. I changed the filter and gaskets and that seemed to take care of the leak on the filter.

Here are my questions:
Is there anything about kerosene that would make it leak more than #2 fuel oil? It seems a little thinner than #2 and I thought it may leak in colder conditions. Kinda the way PEX piping can leak a little when it's cold. The basement was chilly, maybe in the 50s. Or could it sneak its way through the threads if there wasn't any thread dope?

Was my thread dope idea ok? Some guys like the stuff and some guys don't. What's your take?

Thanks

[hvacvegas]

Did a call at a home today. The owner said there was fuel leaking from the fuel lines near the burner. Obviously that's dangerous so I was sent right over.

Everything looked brand new. New fuel lines, new shutoff valves, new filter can etc.

The furnace was in the basement, the old one had originally been inside the house. I found a few very slow leaks, very very slow. A drop would form maybe every 5 minutes or so on the bottom of the shutoffs and around the gasket on the filter. I took apart the offending flare joints and it looks like the guy who did the install did a good job. No splits, cuts, burrs or any of that. When I put the flares back together I put a little pro-dope on them since I couldn't think of anything better to do besides tighten them down as best as I could. I changed the filter and gaskets and that seemed to take care of the leak on the filter.

Here are my questions:
Is there anything about kerosene that would make it leak more than #2 fuel oil? It seems a little thinner than #2 and I thought it may leak in colder conditions. Kinda the way PEX piping can leak a little when it's cold. The basement was chilly, maybe in the 50s. Or could it sneak its way through the threads if there wasn't any thread dope?

Was my thread dope idea ok? Some guys like the stuff and some guys don't. What's your take?

Thanks

You should never put any type of teflon based sealants on flare fittings.
A flare fitting is designed to have a copper/brass connection, like a union. Any impurity that gets lodged between the flare face and the male flare has the possibility of leak.

It's like applying pipe dope to the face of a union. It's wrong, and is asking for problems.

Teflon is for threaded pipe, and very specific applications.

Second, what the heck is kerosene doing in a furnace?

[pacnw]

I agree with hvacvegas on the use of any dope/tape on flares.

kerosene, or #1, is used in place of #2 if the tank is located outside, someplace where #2 would gel/freeze.

if tank is in the house/basement it should not need #1, #2 should be fine.

[mason]

^ agree with previous postings, flares and unions can be lubricated with oil, zoom spout in my case, so that the surfaces don't "catch" or warp during tightening.

[beenthere]

Yep, flare connections are metal to metal seals, no dope or sealant is required, nor should be used. Look for under or over flared ends.

[timebuilder]

I agree with hvacvegas on the use of any dope/tape on flares.

kerosene, or #1, is used in place of #2 if the tank is located outside, someplace where #2 would gel/freeze.

if tank is in the house/basement it should not need #1, #2 should be fine.

Back in my oil days, I had several customers with outside tanks who ran #2.

Most of my kerosene customers were in mobile homes.

Apparently, there is a choice of nozzles and perhaps combustion chambers that are used for kero, and other choices for use with #2. You can cut #2 with some kero in really low temps to reduce gelling, but more frequently, we would offer a bottle of additive to control gelling.

That was 20 years ago, when we used to get some pretty cold winters in this part of the country. A 3° overnight temp was not unusual. For the past decade or so, I can't remember a 3° night.

[beenthere]

Last winter we had a -6°F temp one of the mornings.

I go back a bit further to the 70s, and remember when it was normal to have 2 weeks of 0 and colder weather every winter. Kerosene was put in all outdoor tanks then by most people. those who tried to save a couple dollars by only getting #2, ended up spending that money plus by paying for a service call, and a few gallons of kerosene to be added to thin it down to get the tank to thin out.

Even had to remove a line or 2, and thaw it in my truck. But never any problems with the flare fitting leaking because it was kerosene instead of #2.

[Joehvac25]

The flare should should be air tight, which would mean liquid should not flow trough. On any union or flare oil is the best even in compression fittings.

[timebuilder]

Last winter we had a -6°F temp one of the mornings.

I go back a bit further to the 70s, and remember when it was normal to have 2 weeks of 0 and colder weather every winter. Kerosene was put in all outdoor tanks then by most people. those who tried to save a couple dollars by only getting #2, ended up spending that money plus by paying for a service call, and a few gallons of kerosene to be added to thin it down to get the tank to thin out.

Even had to remove a line or 2, and thaw it in my truck. But never any problems with the flare fitting leaking because it was kerosene instead of #2.

Wow, what a difference that 50 miles can make. We never went below 5° last year that I saw.

I loved the in-ground tanks with a two line setup. Nearly trouble free.

[beenthere]

Wow, what a difference that 50 miles can make. We never went below 5° last year that I saw.

I loved the in-ground tanks with a two line setup. Nearly trouble free.

Yep, no muss no fuss.