LP fired boiler s and furnaces and cold weather

Jamie Hall

Before you panic... it comes up from time to time, so a sort of general note. If you find you are having loss of combustion during the heating cycle in low temperatures, using an outdoor tank and LP gas, check the gas pressure during the cycle -- not just at the beginning. LP vapourization in cold temperatures is reduced, and can cause gas pressure problems as a cycle continues.

DZoro

Good to keep LP tank in really cold climate above the 30% level. Helps prevent some freeze up of the regulators.....

ChrisJ

So what do you do when outdoor temps droop to -20 even -30f?

DZoro

Those are the temps that I'm referring to. Just helps keep good pressure in the tank.

EBEBRATT-Ed

Worked on a large propane job a few years back. It was probably (3) 2000 gallon propane tanks out on a concrete slab. They had 2 gas fired (propane obviously) heaters that they pumped propane through it to warm up the gas and recirculated it back into the propane tanks. They just had atmospheric gas burners on them out in the open. Seemed kind of weird but I guess they do it all the time.

I know tank size and recommended propane withdrawal rates are interrelated

DZoro

On large systems they actually draw liquid from the tanks and then go through a atomizer which is basically a furnace to take the LP liquid to gas.. Unfortunately if they don't perform properly it will destroy many negative pressure gas valves on our high efficient boilers :{.......

ChrisJ

At what point does a standard outdoor tank stop working? -40?

DZoro

LP tanks work with pressure, the pressure in the tank causes the flow to the building. First stage regulator at the tank is usually a 10psi regulator supplying that pressure to the 2nd stage reg at the home. So that being said the tank must be more pressure than that 10 psi that is needed to keep flow. I'm not sure what the pressure/temperature chart is on LP gas. I do know that in the summer tank pressures are well above 110psi. Too cold to go out and check now, we are currently -10*F. Don't recall in my day if in Wisconsin hitting 40 below. I do recall -32 a few years back on some late nite service calls.....

Jamie Hall

Try this for capacity...

The rule of thumb for calculating the vaporization rate from a tank is: (tank dimensions must be in inches)Vaporization in BTUs = tank diameter X tank length X factor (based on the liquid level of propane in the tank at one-third of the tanks capacity at specific ambient temperature)


Factor table

Ambient temp. factor
20F = 131
10F = 110
0F = 90
-10F = 70
-20F = 48

Works for horizontal tanks. For vertical cylindrical, instead of tank diameter by tank length, use tank diameter squared/4 times pi (3.14)

lchmb

Ebebratt-ed they are called vaporizer's. We also use electric. Basic idea is like a water heater..just with an explosive gas..;)

https://algas-sdi.com/resources/more-about-transportable-gases/why-use-a-vaporizer

Solid_Fuel_Man

L.P. is just like refrigeration, just a bit easier to grasp as there is only one phase change taking place.

The wetted surface of the steel tank must absorb heat from the surrounding atmosphere, weather that is the earth in the case of direct burial tanks or the air in the above ground tank example. That absorbed heat will allow the liquid to boil and vaporize into a gas which flows to the regulator, technically as long as it's above the 11in.Water column, or 1/2 psi, the system should still operate, we are talking small residential loads here of less than 250,000 btu.

The outdoor burners you are talking about are called vaporizors. I have installed 3 types, direct fired, hydronic, and electric. Vaoprizor systems are used on large BTU systems. Liquid in drawn from the bottom of the tank via a fitting or a dip tube. It then goes to the vaoprizor where it is heated and turns to a gas where it is then sent I to the building to be burned. Liquid withdrawal systems don't rely on the wetted surface of the tank to boil the liquid therefore are almost freeze proof, I did say almost.....

Most of the time having the tank filled will add to the wetted surface area and solve vaporization issues on those cold days. Having additional tanks or a different style tank can help as well. Horizontal tanks have more wetted surface area per given volume of liquid than vertical tanks. I could go on and on about propane, it is one of the things i love, other than burning wood of course!

Merry Christmas!

FranklinD

Our municipal garage has a propane backup heat system & generator with a pair of giant tanks out in the back yard area, about 100 ft from the building. Not sure on the tank capacity, but they are horizontal, about 4 ft diameter, and 25-30 feet long.

Anyway, they use an electric vaporizer out there on the concrete pad between the tanks, then a pair of 2” black steel pipes brings it to the building.

The system rarely gets used since it’s for backup only... but last winter, the power was out for 3 days after our main transformer went KA-BOOOOM right outside my shop door (very exciting!). It was -25°f not counting wind chill that week, so we needed the heat and the power from the backup propane system.

The backup system worked for all of 2 hours before the (circa mid-80’s) vaporizer went all poopy on us. As it turns out, no local repair techs keep parts on hand for such a device! They rigged something up in the cabinet that seemed to work, at least intermittently, until a new vaporizer could be delivered and installed the next day. And holy hell was it expensive! I seem to recall it being 5 figures installed.