How large should the orifices on my BBQ be?

May 11, 2009 1:31 PM

How large should the orifices on my 52,000 BTU (4 burner) natural gas BBQ be? How long should it take to heat up to 500F?

I know you may not be a gas fitter and you are definitely not my gas fitter, but I am trying to convert my new propane Broil King Sovereign XLS 90 (http://www.broilkingbbq.com/grills/series_15.html) to natural gas. Google has told me that the orifices on the valves need to be widened, since NG is regulated at a much lower pressure than liquid propane. I've had a gas fitter friend of my dad come and swap the propane regulator for a NG hose and hook it up to my supply, but he only widened the orifices from a #57 bit size to a #55 bit size.
Each of the main burners are rated to output 13,000 BTUs, while the side burner is rated at 10,000 BTUs and the rear is rated at 18,000 BTUs. What bit size should I use so that I get the proper power out of my shiny new toy?

Finally, I came across this semi-helpful chart on the web (http://www.joppaglass.com/burner/lowp_chrt.html) but I believe my gas line (Toronto, Ontario) is regulated at 2.5" WC.

So, is there anybody knowledgeable with gas and BBQs that can help me crank the power of my grill without melting the entire box?

posted by aquafiend to home & garden (4 comments total)

Broil king lists the ng and lp orifices in the assembly guide. Personally I would call them to see if they would tell me the ng orifice size. Escalate to tech support if the phone drone wont help.
Tell them your wacky uncle Eric is going to guess, if you can't tell him the right orifice size.

I am a gas tech (fireplace's not bbq's), in the states they have to tell me the size. How can I know the right orifice is in there when I am on a service call? It's a safety thing.

Also keep in mind that although the burner is the same in both the ng and lp models (988744 LP / 988747 NG ) the control assembly (valve manifold) is different depending upon gas type. This may misbehave with a different gas type/pressure even if you get the right size orifice.
Also the ng model wants 7" wc and there is a 1-800 number in the manual.

Be safe.
posted by blink_left at 8:26 PM on May 11

Hey blink_left, I had aquabee post this for me 'cause my week long grace period isn't over.

I've called the manufacturer and they are very reluctant to give me the orifice size. They say the only option is for me to order the complete control assembly. Though I did get them to admit, with much badgering, that the only difference between the control assemblies is the orifice size.

When you say the NG wants 7" WC, what do you mean? They design they're BBQs for a supply with 7" WC? I don't think the pressure in my line is that high.

Thanks for the info so far.

On a more general note, how long should a 52,000 BBQ take to reach 500F? Just so I have some way to see that I am on track.
posted by consummate dilettante at 6:50 AM on May 12

"When you say the NG wants 7" WC, what do you mean?"
Page 3 of the manual for the NG version "The appliance is designed to operate at a regulated pressure of 7 inches water column (W.C.)."
The link on the web page only goes to the lp manual, but search for 988747 for the NG manual.

I dug up a chart that calls a drill size:

DRILL SIZE |DRILL in INCHES| btu NATURAL GAS | btu PROPANE

62 0.0380 3,666 10,087
61 0.0390 3,862 10,625
60 0.0400 4,062 11,176
59 0.0410 4,268 11,742
58 0.0420 4,479 12,322
57 0.0430 4,695 12,916
56 0.0465 5,490 15,104
55 0.0520 6,865 18,888
54 0.0550 7,680 21,131
53 0.0595 8,989 24,730
52 0.0635 10,238 28,167
51 0.0670 11,398 31,357
50 0.0700 12,441 34,228
49 0.0730 13,530 37,225
48 0.0760 14,665 40,347
47 0.0785 15,646 43,065
46 0.0810 16,658 45,831
45 0.0820 17,072 46,969
44 0.0860 18,778 51,663


500F? All burners on, half an hour?

Hth
posted by blink_left at 12:16 AM on May 13

Thanks for the info. I called the manufacturer and after much pestering and escalation they told me that only the "engineers" had the information and that they will not disclose it.

Anyway, I found a chart online which matches the excerpt above. The BTU NG column is for 3.5" WC in the above chart.

The manufacturer did tell me, however, that the BBQ should take about 10 minutes to reach 500F.

I'm gonna try again tonight, and let you know how it goes.
posted by consummate dilettante at 6:33 AM on May 13