Calculating propane usage

[WolfWhistle]

This is probably old hat to many, but first time I realized how "one" could estimate how long your propane could / should last.

Did you know that a gallon of propane (Liquid Propane, if you prefer) has about 91,500 BTU (British Termal Unit) of energy per gallon?

A full (80%) 20 # cylinder holds 4.7 gallons of propane; a full 30 # cylinder holds 7.1 gallon or propane, again with a good fill.

So about the calculations.

So, with 4.7 gallons in a 20# cylinder contains 430,050 BTU of energy... a 30# 649,650 BTUs.

All appliances should show their BTUs (per hour).

My furnace 19,000 BTU/hr... water heater 12,000... etc.

Dividing the BTU / hour of the appliance tell you how long this appliance could run continuously on the tank. The trick is estimating how long they run per hour. You know how long a furnace might run or how long you used the stove, but a water heater would be harder to tell.

So, if you divide 430,500 by 19,000 (some know where this example comes from ) it tells us we should get a little over 22 hours out of that 20# tank of continuous use. If it ran 30 minutes per hour, we could get 44 hours of heat from one tank, in theory.

A 45,000 furnace would run a little over 2 (TWO) hours from a tank. It is obvious and eveyone knows a 20# cylinder has no place in big RV. But, seeing the number is interesting.

This water heater alone (12,000 for the Dometic 6 gallon) could run 35.8 hours continously.

My little 6,000 catalytic could run over 71 hours.

Propane weighs 4.2# per gallon, by the way, so 4.7 gallons weighs about 19.7#. The empty tank weight is about 17#, which is also called tare weight. Add together, a full tank should weigh around 37# or slightly over. The 30# weighs about 55# total.

Did you know that companies that exchange cylinders (20#ers) underfill them, "full" might only be 3.5 gallons? If the price is low enough it still could be less exensive than having a gas company fill yours. Personally, I would rather keep my tanks and only exchange if is an emergency.

I need bigger tanks! I need a raise.

Sorry.... my OCD (CDO) is glaring, huh?

[breezyhillfarm]

I got into camping so I wouldn't have to do math! Actually I just use one tank until it changes to the other and fill the empty one. If I'm on the road and away from a propane facility I'll use the rhino exchange.

Since I'm mostly a weekender it has worked. If I'm out more it may be worth tracking closer.

[pt1655]

Wolfwhistle,
Geez, great writeup. For me personally, I bought 2 tanks from Costco that have the gauge included and just go by that. Sigh.

[rana]

Originally Posted by breezyhillfarm

I'll use the rhino exchange.

One caution with the Rhino and similar exchanges... they use proprietary valves that prevents you from being able to refill those cylinders at any ol refill station.

Once you're in the exchange system, you're stuck with having to use it exclusively.

[Oaklevel]

Wow you are over thinking this thing........

All I can tell you is we use two 30 lb tanks a year camping a total of about 30-40 days. On our 36 ft. Puma TH. Closest to winter we now get is Thanksgiving week. Filling them last year at the local Exxon Station was at $22 ea. Getting ready to fill one from last year so will see what the price is this year.

Our 1988 22' camper running the furnace & everything else would last a week cold weather on a 20lb tank.

Really too many variables to do too acurate of calcuations.......

[rana]

Originally Posted by pt1655

Wolfwhistle,
Geez, great writeup. For me personally, I bought 2 tanks from Costco that have the gauge included and just go by that. Sigh.

Those pressure type LP gauges though are about as accurate as an RV's black tank sensor.

Tank pressure is affected so wildly by the vaporization characteristics and boiling point of LP within the tank, convective heat transfer from the area of the tank up to the level of the liquid LP, temp differences between the ambient air and liquid LP itself in order for the LP to extract enough available heat to allow vaporization... not to mention regulator demand and whether or not all of the above will allow the tank to maintain equilibrium or not.

As far as I know there are only four ways to accurately measure LP levels in a tank. Thermal strips, weighing, IR, or ultrasonic meter.

I love my Truma!

[jkochmit1]

I have heard if you pour warm water on the outside of the tank you can tell how full it is by where the condensations starts not sure if its true and have not tried it yet.

[rana]

Originally Posted by Oaklevel

Really too many variables to do too acurate of calcuations.......

Exactly!! And those variables are constantly changing.

Math might get you in the ballpark, but LP consumption is fairly user/rig specific. The best bet is to get a tank weight, go about your business, record daily weights over a period of a couple of weeks, then calculate your average consumption. Once you have daily averages for the various seasons of the year it's not too difficult to guesstimate your LP needs for any given get-a-way.

[rana]

Originally Posted by jkochmit1

I have heard if you pour warm water on the outside of the tank you can tell how full it is by where the condensations starts not sure if its true and have not tried it yet.

Kind of. If you pour HOT water over the side of your tank then run your hand down the side of it, you can often feel a temperature change between the vapor and liquid levels. The warmer it is outside though the more difficult it can be to feel a change.

[camping baba]

The math looks good but the appliances do not run 100 percent efficient . The best that they are going to run will be approx . 75percent. So you will have to add that to the usage .

[Jim Schings]

Yarome,

Not actually. All new tanks produced after 2002 have to have the new Overfill Prevention Device (OPD) valves on them. Many refillers won't/can't handle the old stuff and all of the exchange places use the new OPD valve.
They aren't proprietary. They are GOV mandated. You CAN replace the older valves with the new OPD ones, but it isn't worth it. For $25 most all of the exchange places take your tank in exchange and give you a new tank full of propane. I just did that at a Tractor Supply, and they told me the Rhino down the street does the same.

Originally Posted by Yarome

One caution with the Rhino and similar exchanges... they use proprietary valves that prevents you from being able to refill those cylinders at any ol refill station.

Once you're in the exchange system, you're stuck with having to use it exclusively.

[camping baba]

Tanks are good for 12years from the date they were built . At that time the need to have an inspection every 5 years after that .

[rana]

Originally Posted by Jim Schings

Yarome,

Not actually.

Actually.. yes. It doesn't have to do with the OPD valve requirement. Blue Rhino uses their own TS2 (Tri-Safe II) OPD valve on the majority of their cylinders that can not be re-filled by normal propane suppliers. It requires a magnetic key that must be inserted into the indentation in order to hold a steel ball out of the way.

Directly from Blue Rhino:

"Blue Rhino is the leader in the industry for providing the safest tanks on the market. Some, but not all of our tanks have a special safety device that prevents the refill by anyone other than a Blue Rhino specialist. They are called TS2 cylinders. The reason we designed them is simple. It's for the safety of our consumers!! We stand behind our product. We know how our cylinders are filled and that the highest level of accuracy and safety checks are performed. When our consumers take our cylinders and have them filled elsewhere, we cannot be liable or guarantee the safety of that cylinder. If your tank is not properly filled, damage to your valve can result, which can prevent it from performing properly.
Our business is propane cylinder exchange. We recommend that our customers only exchange because of the safety/liability issues associated with someone else filling our tanks. However, you, as a consumer, are free to fill your cylinder if you wish. Not all of our tanks offer the special safety feature. The way to identify the special TS2 valve tanks that cannot be filled is easy. If your tank valve has a small triangular indention on the side, then it is "tamper" protected. If you prefer to have a tank that can be filled by anyone, take that tank back to any Blue Rhino retailer and exchange it for one that does not have the triangular indention.
For liability reasons, if you choose to refill your tank, please remember to remove the plastic sleeve before having it refilled.
I hope this information helps."

[Taranwanderer]

While we're in the topic of propane...for those of you in the NEPA area, Modern Gas fills 20# cylinders for $9.95 and 30# cylinders for $15. Good deal.

Propane Gas Sales, Services, Heaters & Fireplaces Scranton, Honesdale, Stroudsburg & Hazleton, Pennsylvania (PA)

Strangely enough, the TSC around here doesn't deal with propane at all, either refilling or exchanging. Wonder why some do and some don't?

[kandl]

Originally Posted by WolfWhistle

Did you know that companies that exchange cylinders (20#ers) underfill them, "full" might only be 3.5 gallons? If the price is low enough it still could be less exensive than having a gas company fill yours. Personally, I would rather keep my tanks and only exchange if is an emergency.

These "propane exchange" outlets (bandits) are no different north of the 49th. You're lucky if you get 15 lbs of LP in a 20 pounder - frequently it's less. That's why we too use our own tanks and will drive the extra mile to find someone who's proficient in replenishing a propane cylinder.

You post was an informative read but painful. I worry more about the temp of the barley pops.

[breezyhillfarm]

Originally Posted by Yarome

Directly from Blue Rhino:

I hope this information helps."

Thanks. I must have gotten lucky as I got my rhino tanks refilled at a campground a couple weeks ago.

[Jim Schings]

Thanks, didn't know that, (nor have I experienced it.) But I will make sure it doesn't catch me..

Originally Posted by Yarome

Actually.. yes. It doesn't have to do with the OPD valve requirement. Blue Rhino uses their own TS2 (Tri-Safe II) OPD valve on the majority of their cylinders that can not be re-filled by normal propane suppliers.

[karrun]

Originally Posted by jkochmit1

I have heard if you pour warm water on the outside of the tank you can tell how full it is by where the condensations starts not sure if its true and have not tried it yet.

I tried something similar this last weekend. I poured hot water down the side, then used my IR thermometer gun and ran it up and down the tank. Saw a definite termperature shift of about 10 degrees where I assume the liquid level is. That's close enough for me.

[WolfWhistle]

I know effeciency is depending on may factors including elevation. But, I would think a furnace rated at 19000BTU is already 50% inefficient. More important to efficiency is the human factor.

[chpence1]

Just get see thru propane tanks.... they are lighter too.....