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Q-talk *ON TOPIC ONLY* QUALITY ON TOPIC discussion of Backyard BBQ, grilling, Equipment and just outdoor cookin' in general, hints, tips, tricks & techniques, success, failures... but stay on topic. And watch for that hijacking.


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Unread 10-29-2013, 09:44 AM   #1
S60
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Default Weber burners not burning stated BTUs

Question: If I am not starving the my grill of natural gas, what could be the reasons for the natural gas burners not burning the full stated BTU rating? Thanks for your thoughts. (Question repeated again at bottom)

Background (not directly relevant to question): Bought a used natural gas Weber Silver C ("NG C") to hook up to my natural gas pipe. I was previously using a propane Weber Silver C ("Propane C"). The Propane C could not be used for my needs on high as it was too hot, easily topping 600 and pushing 650. I typically ran the Propane C on med-high. The NG C got to 550 after 15 minutes of warm up, but struggles to climb back to 550 after opening the lid and putting on some food, such as hamburgers. It’s not a problem as I don’t usually cook at 550 and the burgers cooked just fine at 400-450 which is the temp the NG C reached by the time the burgers were done, having opened the lid and flipped them once. But I would like for the NG C to quickly get back to 550 if I put some steaks on it (like the Propane C could do). So it got me thinking - am I feeding the NG C enough natural gas.

Analysis: I tested the BTU's buy reading my gas meter. My readings are in small increments so the margin of error might be high, but I took two different readings and obtained the approximate results both times so I believe my readings are accurate enough. I am assuming 1 cubic foot of natural gas has 1,000 BTUs. My gas meter’s smallest dial reading is for 1/2 cubic foot. The flame on my NG C burners is mostly blue with occasional flecks of orange at the peaks. The NG C side burner is all blue.

Test 1 – ran the 3 main and the 1 side burner on high and it took 53 seconds to use ˝ cubic foot. That is 9.4 BTU per second. According to Weber, all 4 burners are rated 46,000 BTU (12 x 3, plus 10), which is 12.7 BTU per second. So my NG C burners are putting out only 75% of their rated capacity.

Test 2 – Based upon the results of Test 1, it looks like I am starving the NG C. So I did a second test. This time, I ran only the 3 main burners on high to see if the 3 main burners would use the natural gas that was available to the side burner, based on all 4 burners being fed from the same manifold. To my surprise, the 3 main burners on high took 1 minute 6 seconds to burn 1/2 cubic foot. That equates to 7.5 BTU per second. So the 3 main burners did not use the extra gas available for the side burner. And even with the side burner off, the three main burners used only about 75% of their stated BTU. The main burnes burned the same BTUs regardless if the side burner was on or off.

The NG C main burners are 12,000 BTU, and the side burner is 10,000 BTU. The 3 main burners represent 78.2% of Weber’s stated BTU output for the grill. My testing above resulted in just the 3 burners using 79.8% of the natural gas used by the 3 burners plus the side burner. So at least the NG C is burning BTUs in proportion to Weber’s stated proportions. More importantly, my results show that the main burners are not being starved of natural gas. If they were being starved, the 3 main burners should have used some or all of the reserve capacity available to the side burner that was turned off (this is because I believe all 4 burners use the same manifold so the gas available for the side burner is available for the main burners when the side burner is not being used).

Question: If I am not starving the NG C of natural gas, what could be the reasons for the NG C burners not burning the full stated BTU rating? Thanks for your thoughts.
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Unread 10-29-2013, 10:44 AM   #2
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Natural Gas has an 80% efficiency rating 1.192 BTU's per 1 millionth CF actual BTU are 1.049 per millionth CF
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Unread 10-29-2013, 10:51 AM   #3
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I can't really answer your question, but I have a silver and a platinum weber propane grill, the platinum I like better than the silver because it is hard to get real bad flare up like the silver tends to do. I have put new burners on both so that eliminates that problem. The only difference I can see is the platinum has a much deeper fire box with a double row of flavor bars the silver only has one row of flavor bars. The silver runs a lot hotter than the platinum. I can't take a reading of the btus being used so that is no help either. You may want to take a peek at the header where the tubs fit and make sure they either have not wiggled loose or have some spider web or bugs blocking them, they make bug guards that fit over the ends, and are not very expensive, or could be they need a little adjustment. As I said I have propane and am not familiar with NG, if it has a regulator you may check that for blockage like mentioned. The only other thing you make check is the gas connections, making sure they are not leaking. If you have a gas range in the house it it working ok? meaning does the gas pressure appear ok? Hope someone that knows more than me can help.
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Unread 10-29-2013, 11:50 AM   #4
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Have you tried kicking it or smacking it with a Hammer.....?

Or maybe you have a Dirty Orfice ?
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Unread 10-29-2013, 11:51 AM   #5
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Quote:
Originally Posted by SmittyJonz View Post
Have you tried kicking it or smacking it with a Hammer.....?
Harbor Freight hammer of course
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Unread 10-29-2013, 02:28 PM   #6
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As long as it lights the fire.. Idc if im getting the stated btus lol
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Unread 10-29-2013, 04:14 PM   #7
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I just wonder if the burner holes are not partially clogged. tak a drill bit or a gas welder tip cleaner and ream out all the holes. many times burners will look ok but are actually plugged by carbon deposits on the edges of the holes.
also make sure the inlets are not plugged of spider webs. etc.
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Unread 10-29-2013, 04:36 PM   #8
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Nat gas runs cooler. Most Grill burners are designed for optimal performance with propane. Adjustments for high altitude or nat gas are normally made with an orifice change to the burners to change the air/fuel mixture. A nat gas designed grill will also include a bigger regulator sized for and tuned to a nat gas burner design. I would be surprised if Weber or others specifically have true nat gas burners.
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Unread 10-29-2013, 04:43 PM   #9
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http://answers.yahoo.com/question/in...1091216AA6HHAr

I wondered if someone swapped out a NG line for the propane regulator, but NG orifices are 2.5 times the size of propane orifices. It seems like you would get a lot less than 75% in that case.

The article does mention pressure and that makes me wonder if your natural gas pressure might be low or is there an obstruction in the supply line or the line on the grill. Perhaps the supply line is undersize for the grill. I'd also check for spider webs inside the burner tubes.

Good luck solving this!
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Unread 10-29-2013, 04:54 PM   #10
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1. Check your orifices for proper sizes.
2. If you have a regulator on the line before the grills appliance regulator, it may need adjusting.
3. Be careful with files and tip cleaners as you may increase the orifice.
4. You may not be getting the proper gas volume due to improper pipe installation.
5. The appliance regulator may be an issue.
6. Your math may be off due to whatever. Hint...when trying to calculate such small BTU rates you need to clock the meter a lot longer than you did and do it several times.
7. If other things are running gas inside the home you can test everything to see if you have problems with the meter. *I suggest a professional*


I bet you missed the clock and that is why you are off but it does not take much to stop up the orifices.
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Unread 10-29-2013, 06:07 PM   #11
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I have tow different gas burners the mighty Harbor Freight weed burner and the bic lighter/ pinto bean Buttwiper beer mod. real men cook with Hard Wood
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Unread 10-31-2013, 08:33 AM   #12
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Thanks for your thoughts and suggestions, which has lead me to my hypothesis, which I hope to test out this weekend - that the natural gas pressure at the grill is lower than the pressure for which the natural gas orifices were designed (i.e., the issue is pressure, not volume).

This is never an issue with propane grills, as the propane pressure delivered to the grill is a consistent 11 inches water column regardless of the volume of propane in the tank (until the tank runs empty). But for natural gas, at least for this model of Weber natural gas grills, there is no regulator to control the natural gas pressure. Rather, this model is relying on whatever natural gas pressure is provided to the grill. Houses typically have a whole house regulator that brings the street pressure down to between 5.5 and 9.5 inches water column, with most gas companies aiming for a 7 inch water column pressure entering the house. To the extent any particular appliance requires a lower pressure, such as a stove top, the stove top will provide its own regulator to further reduce the pressure to say 3.5 inches water column.

Back to the Weber. The manual says the grill was designed to operate at 7 inches water column. On the BTU orifice size chart, that translates to an orifice size of about 53 (by comparison, the orifice size the Weber propane version of this grill uses is 59, a smaller size to account for the higher pressure). This means that if the natural gas pressure at the grill is higher or lower than 7 inches water column, the Weber natural gas grill will produce more or less BTU’s depending on the natural gas pressure.

I see that some newer models of Weber natural gas grills are designed to operate at a lower 4.5 inches water column and Weber supplies a regulator to reduce the pressure, if necessary, to 4.5 inches water column. This seems to be a better design, as like propane, it attempts to guarantee that the correct pressure of natural gas is always being delivered to the grill based upon the theory that there should typically always be a higher natural gas pressure available to the grill than the pressure at which the grill is designed to operate, and the regulator reduces the pressure to the correct pressure.

My grill is only producing 75% of the stated BTUs, or about 9,000 BTU’s per burner (the manual says there should be 12,000 BTUs at 7 inches water column). According to the BTU orifice size chart, the Weber was designed with a size 53 orifice. Looking at the chart, a size 53 orifice produces about 9,000 BTUs at a pressure of 3.5 inch water column. Looking further at the chart, in order to burn 12,000 BTUs at a 3.5 inch water column, the orifice size needs to be about 50.

So my first step is going to be to clean out the orifices. If that does not work, then I will give some thought to drilling out the orifices to a size 50 (replacement orifices are only a few dollars on the internet if I ever need to reduce the orifice size back to 53). Before I do the drilling, I am going to rerun my tests to make sure my calculations are correct, and that the presumed pressure of 3.5 inches water column at my grill is consistent and not the result of a fluctuation in gas pressure entering my house on the day I ran the tests.

Thanks for all your help and suggestions.
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