Another question we hear a lot from customers is why their gas fireplace or gas fire pit keeps losing its flame or going out completely without and control. I was first given this question by a very good customer. The guy had purchased a lot of custom products from us and I really felt bad about his fire pit having problems. I went to a few of the “wise-old-men” in my industry to ask them because I did not know. Like a lot of people thought to be wise some of them made up answers by saying the regulator was bad or the fire pit valve needed to be replaced. Others simply said they did not know. I could not find an answer.
I started replacing parts which was expensive financially and took a lot of time. My customer was not too mad because he saw all the work we were doing to determine an answer. As we were replacing parts I was also doing research into how the valve worked, how the regulator regulated gas flow and how the pressure acted within the fire ring burner in the fire pit.
Eventually I discovered the answer but when I checked my answer with several other gas technicians no one knew what I was talking about. Fortunately this was many years ago and by now time and testing has proven the research and the tests I ran determined the right answer. I discovered why the fireplace burner and fire pit burners were losing flmaes and going out.
Each of my fire pits that had this problem were using propane gas. Propane gas has — by law! — to have a safety valve control with a pilot flame and a thermocouple. Many builders make fireplaces and fire pits without a pilot and withou safety features but we do not. The liability is too great if someone ever gets hurt. Unfortunately the valve, safety solenoid, thermocouple all gave me extra parts to suspect of fsailure as we were struggling to find out what was wrong with out fire pit.
Each of the gas fireplaces and fire pits I have had this problem with was using the standard LP cylinder that
we all use on our barbecue grills. These tanks are everywhere and can be easily filled or exchanged all over town. However, LP stands for Liquid Propane. Propane is a Liquid that boils at a very low temperature. What is freezing cold for a human is boiling hot for liquid propane. LP cylinders are designed to vaporize liquid into gas around the circumference of the LP tank. This is what gives LP cylinders their shape. The gas vaporizes (boils) along the inner walls of the tank. As I was reading this research material that described how, where and at what temperature propane turned into gas the materials also described the tank design and how different tank designs were more or less effective than the common 5 gallon tanks we all use.
It occurred to me that if it were possible for one type of cylinder to be more or less efficient than another type of LP tank cylinder then there must be a way of measuring how much or how fast liquid turned to gas. I will not go though the entire detective story other than to say I had to go through a lot of places and run a lot of tests to get a straight answer. The answer is also a constantly changing amount because humidity, altitude, and quantity all affect the vaporization rate. For instance one ice cube in one bowl will melt so fast but 100 ice cubes in one bowl will melt at a slower rate because the quantity of cold ice will help each individual cube stay cold as the warmer air works in from the outer edges.
A standard 5 gallon LP tank can typically vaporize at an average of 55,000 BTU. If a gas fire pit is pulling 90,000 BTU (which is normal) then the valve is allowing more gas vapor through to the burner than the liquid can change into gas. If the flames are no pulling too hard then at some point the gas vapors will diminish and flames may drop from burning 8″ tall to burning 2″ tall. When the flames are very strong on a larger burner and a full tank it is dangerously possible for the liquid propane to get sucked through the valve.
Liquid propane is freezing cold — cold enough to burn our human skin and cold enough to turn water vapor in our air back into ice. When this happens the regulator and the gas line on the fireplace or fire pit will be extraordinarily cold and sometimes ice will form on the regulator and gas lines. The fire pit will burn for awhile because there is already a reservoir of vapors in any LP tank and the liquid will immediately start vaporizing as the reservoir gases are pulled out of the cylinder. This is why the burner flames will burn for 10 minutes or even an hour (a half-full tank has more of a reservoir than a tank that is almost completely full) before dropping in intensity or going completely out.
In order to get the fireplace and the fire pit working as our customers want them to function we have to provide more gas flow.
Many technicians believe a double stage regulator will help and that is tru but the difference is so minor as to
be completely indistinguishable from the problem. The 2 stage regulator is a regulator that limits gas flow in stages. There are many different types of regulators but a typical regulaotr for propane limits gas flow to 11″ water column displacement. Most regulators have a single round chamber that only allows 11″ of pressure to pass through it in order to regulate gas flow. A 2 stage regulator is the same in that gas comes in at a higher pressure and comes out at 11″ but the 2 stage has 2 chambers. All this really does is increase the upper limit of the regulators effectiveness. A regulator will break if the gas pressure coming into the regulator is too high. A regulator can step down 1 pound per square inch down to 11″ (about 1/2 pound) but that same regulator cannot step down 10psi to 11″. This has to be done in stages. A 2 stage regulator will not make a difference when it is inbetween a 90K BTU burner and a 55K BTU tank.
What we have to do to make the fire pit work better is use a tank with a larger inner circumference. A 10 gallon tank is often called a 40 lb tank. They look just like standard tanks but they are taller. A taller tank is no good because fire pits are generally built low to the ground and 40 lb tank is too high to go under a dining table. The benefit to us is that a 40 lb tank is also available as a horizontal tank.
As an aside there is a 40 lb horizontal tank commonly used on forklifts but forklift engines pull liquid propane as well as vapor propane so we cannot use these forklift tanks on gas appliances.
A 40 lb horizontal LP tank is capable of vaporizing approximately 95,000 BTU. This is usually enough for a fire pit. If the customer has NG at the home that can be regulated to have no limits and we can use our control valve and orifice to control gas pressure which is what those controls are made to do. Also many homeowners have 100, 500, 1000 gallon LP tanks buried underground or mounted on the side of their house. This gas is also able to be regulated to provide unlimited to our low pressure appliances so the
controls will control our flame height instead of running out of gas.
The other option is not a option any customers ever want to hear. We can put a smaller orifice on the gas valve so the valve does not pull more gas flow to the ring burner or to the fireplace burner. This will stop the burner from running out of vaporized propane but it also severely limits the appearance of the gas flames — and the whole idea of the fire pit os cool-looking gas flames.
Today when we accept a job to install and to build a custom outdoor fireplace or fire pit we do not allow the opportunity to use a standard LP tank. We build in the cost of a 10 gallon tank into our price. We always use a 40 lb horizontal gas tank on fire pits that need a portable tank because to use a smaller tank means the burner either runs out of gas or barely burns.
Every once in awhile a customer will complain because a 40 lb tank is not as easily carried around as a smaller tank when it is time to have the gas refilled. Also every gas station and retail store in town does not have exchange tanks available for 40 lb cylinders. These are the drawbacks and they are minor. We can fill the tanks for our clients or help them get a fill station but the easy-to-use and reliable fireplace or fire pit is definitely worth a little annoyance filling the tank once or twice a year.