Heating elements use a lot of power to get the job done, and it's not a very efficient way when you have limited energy. Most RVs use propane gas as their energy source for heating and cooking, and their refrigerator if they can.
I bought a wood stove for heating (which has it's own pros and cons), a Natural Gas / Liquid Propane cooktop (that needed to be converted to propane), and I have a refrigerator that can run on electric power as well as propane.
The most helpful way for designing your space is having your appliances in advance, if possible. I realize storage for appliances is difficult for a lot of people - but if you could do it, I recommend it. Knowing your appliance's gas usage is crucial for understanding how much gas you will use. Every appliance is different, how you use it will be different than other people, and such. But hopefully I can give you some general information that has helped me.
Your propane system must have:
- At least one propane tank
- A two stage regulator
- Main shut off valve
- Shut off valves for each appliance
- Gas lines that run from your shutoff valves to your appliance regulators
Determining Propane Usage:
Okay, so there's a little bit of math and terminology to learn before we can know how much propane your appliance actually uses, and how much you would need.
The combustion value (the possible amount of energy we can obtain per unit of propane) is called a BTU. For example, 1 gallon of propane has 91,500 BTUs. The potential amount of energy we can use, per gallon of propane, is 91,500BTUs.
It is important to view our propane system by units of energy because appliances that use propane are rated in how many BTUs they use to operate, which will tell you through conversion how much physical propane they use per hour.
Here is a picture of my refrigerator's inside tag:
So my fridge uses 1,500btu per hour. A 20lb propane tank actually contains 4.7 gallons of propane, or if we convert it is 430,050BTUs. [4.7gallons * 91,500(BTU per gallon) = 430,050BTUs]
So we know it will use 1,500btu per hour. For a 24 hour period, that's 36,000BTU per day.
Now that's assuming the fridge runs constantly, which isn't realistic. Most refrigerators will turn their pump on occasionally throughout the day to cycle refrigerant through the lines when the temperature regulator inside the fridge notices a temperature change. I couldn't find any specific data about my refrigerator to tell me how often it cycles, so I took a conservative guess; I would assume based on the size and how often I open it (big factor in lowering temperature), that it might run for 15 minutes and cycle every two hours. I would rather compensate for a non-ideal situation than not right?
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So if it's 1,500 per hour then we divide that by 60, giving us how much it uses per minute, which is 25btu. If it runs for 15 minutes, then it's 375btu every time it cycles. (25 x 15 = 375)
If it turned on/cycled every 2 hours, that's 12 times a day. 375 x 12 = 4,500btu per day
So a more realistic usage for our fridge, cycling 12 times a day, is 4,500btus. (which is a huge amount actually. It shouldn't cycle that often, and probably wouldn't run for 15 minutes each time either.)
A 20lb propane tank has 430,050 total BTUs
430,050 - 4,500 = 425,550
425,550 / 91,500btu per gallon = 4.65 gallons left
4.70 original gallons - 4.65 = 0.05 gallons used per day
0.05 x 28 = 1.4gal per month/28 days
4.70gallons / 0.05gallons per day = 94 days per 20lbs tank for refrigerator only
So now we know how much propane our refrigerator will use, and how long that will last (conservatively).
Every one of your appliances that uses propane will have a BTU rating, and unless specified is rated per hour. Some appliances like a cooktop have multiple BTU outputs because the burner orifices are different sizes, and that makes it a little more complicated to know how much propane you would use.
Although it's true that nothing is 100% efficient, the BTU draw for an appliance this small makes the difference in extra propane consumed negligible. If it's only 80% efficient, then that puts me at 1,800btu an hour instead of 1,500 - converted down that means I use 0.01gallons more.
This is the numerical data I have for my setup:
Fridge: 4,500btu a day | 0.05gal a day | 1.4gal per 28 days
Cooktop: (most realistic is 30min a day with two main burners)
10,000btu main burner / 60min = 166.6 per min x 30min = 4,998btu
8500btu / 60min = 141.6 per min x 30min = 4,248btu
4,998 + 4,248 = 9246btu
9,246btu a day | 0.11gal a day | 3.08gal per 28 days
Water Heater: 15,700 - 41,000btu per hour / Average 28,350btu per hour | 472.5btu per min | 15min shower = 7,087.5btu
Total daily usage: 33,827.25btu | 0.38gallons a day | 10.64gallons per 28 days
My 30lb propane tank with my 20lb propane tank is 11.7 gallons of propane, or 1,070,550btu total.
1,070,550 / 33,827 = 31.64 days at 33,827btu per day
Now that you've done this for all your appliances, now you know how much propane you'll be using and you can decide on what size propane tanks you need based on how long you want to go without having to get refills. You don't have to go through the numbers like this if you just want a general idea; most large LP burner orifices for cooktops are 8,500btu, ovens are 10-12kbtu, water heaters have a range based on how hot you want them - but they never run at full strength, and refrigerators don't run constantly so that's a variable as well.
Regulators:
Regulators are devices that regulate the pressure inside your propane tanks to a lower consistent pressure to be distributed throughout your gas lines to your appliances. The pressure, or PSI (pressure per square inch) inside a propane tank can fluctuate from 100 to 200+ PSI based on the temperature outside. You absolutely need a main regulator if you're using propane tanks. Their internal PSI will fluctuate and will not provide a safe consistent pressure for appliances on their own. This is why you need a main regulator, and a regulator for each appliance as each appliance requires different propane pressure.
A two stage regulator is required in RVs here in the United States; Two stage regulators are a type of regulator that will lower the pressure from the tanks to a consistent pressure at the first stage, and then regulate and continuously keep the pressure inside the gas lines at 11"WC past the second stage. The benefit of a two stage regulator is the second stage of the regulator will always make sure there is consistent pressure to your appliances - especially appliances that require a non-fluctuating pressure at all times like your refrigerator.
What is Water Column?
The gas pressure appliances are designed to run on is rated in something called Water Column, abbreviated as W.C. We needed an easy way to measure small differences in pressure in a system, so we created a unit of measurement that was based off the density and behavior of water under pressure.
Water column is the amount of pressure it takes to raise a 1-inch x 1-inch column of water by 1 inch. This unit of pressure measurement is ideal for equipment with low operating pressures, like a small refrigerator. It's best suited for expressing minute pressure differences across pipelines and shafts, and in this case small diameter gas lines.
It's essentially like the difference of measuring time with minutes vs seconds. If the pressure difference is small, then determining the step down in pressure needed for a refrigerator is a lot easier to calculate when we use a general measurement like WC instead of taking into account the diameter of the pipe x inlet pressure x outdoor elevation, etc.
It would seem easier to just have all equipment, like RV regulators, just put out the pressure that appliances use; luckily they are designed that way, and many two stage regulators are pre-adjusted from the factory to put out an 11"WC pressure after the second stage. Here is a photo of my refrigerator's tag again:
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| "Manifold Pressure of 11"W.C" is the pressure of propane that my refrigerator runs on |
The two stage regulator I bought is pre-set to 11"W.C after the second stage, so my refrigerator should have no problem. If your appliance runs at 10"W.C, like my cooktop, then your appliance will need it's own regulator that lowers the pressure again to 10"W.C before it enters the appliance.
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| My cooktop's regulator |
You see at the top right of my regulator it says (Nat 4.0" LP 10.0"). This means the pressure for natural gas is 4"WC and for Liquid Propane is 10"WC. This type of regulator can be converted to either natural gas or propane, but I'll talk about that in another article for cooktop conversions.
BTU Output for Regulators:
Alright so we understand that we need to lower the pressure from the tanks with a main regulator, and may need regulators for appliances that run on different water column pressure, so how do I know the size of a regulator I need for all my appliances?
If you've looked around at regulators you'll see they're usually advertised by their BTU output, meaning the max amount of BTUs they can supply at any given time. This is important because you will need a higher BTU output rating than what you actually use, and here's why.
A lot of people will have this problem where their propane fridge is running normally, they're cooking something on the stove, and when their gas furnace kicks in it will shut their fridge off. What's happening?
Although we may have a consistent 11"WC in the lines - if we're pulling too many BTU at one time (using more gas) than the output is designed, it will lower the overall pressure of the line and your appliances that require a constant pressure like your fridge will shut off. In my fridge manual it mentions that the W.C must be at 11” at 50% available usage - meaning that the BTU output of the regulator has to be at least 150% of what I would actually need, so in case I'm using 50% of possible BTU output it wouldn't affect the overall pressure of the line.
We know that my btu usage per day is 33,827.25btu, but we want to know what's the absolute maximum amount of BTUs we could use at any given time:
Appliance BTU usage per hour:
- Fridge: 1500 BTU
- Cooktop: 31,500 BTU all 4 burners
- Water Heater: 41,000 BTU per hour
Total: 74,000 BTU max per hour
Even though we wouldn't be using 74,000btu, we want the pressure in the lines to be able to handle that type of flow so the WC to each appliance is constant, regardless of use. Since the fridge needs 11"WC at 50% usage, then 150% of our max btu is 111,000btu
74,000 x 0.50 = 37,000 (50% of 74,000)
74,000 + 37,000 = 111,000btu
So the BTU output for my main regulator has to be at least 111,000BTU so even at 50% draw, will not drop the pressure in the lines for my fridge. It's totally fine to have a higher BTU output than you actually use, because your appliances will still only use the amount of gas they're designed to. The regulator will only supply what the appliance demands but can not force more than the appliance can use. You could have a regulator that is rated way more than all the appliances being served and only the volume any one or any combination of the appliances will flow through the regulator. A higher BTU rating is just how much gas it can supply at any given time.
The only downside to a larger regulator is when you adjust them, it's difficult to make smaller adjustments to the output pressure when the range is so large. As you choose a higher and higher pressure propane regulator, the degree of control that the propane regulator valve has over the gas output decreases; i.e., turning the valve an 1/8" in a 0-60 psi adjustable propane regulator has a lot more effect than turning the valve an 1/8" in a 0-20 psi adjustable propane regulator. If you have to adjust your regulator because the pressure is too low or high, I would recommend bringing it to a place that can do this for you. You would have to check the gas pressure when the refrigerator for example is operating, as there is a pressure test port on the solenoid and requires certain tools and knowledge to do safely. As most two stage regulators come pre-adjusted, you shouldn't have to worry about this.
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