check orifice size - propane vs. nat gas
Hi, I suspect the orifices in my boiler are not sized properly - or at least I would like to confirm wthout a doubt the correct size is installed. I have a propane fired Weil-McLain CGI-6. it came from the factory configured for natural gas. When it fired up she sooted up the side of my house. The installer said he changed the orifices over however over the years I can still see some soot now and then. The manual states the correct orifice size for each fuel - something like .129 propane and .075 nat gas (don't have the manual with me). I'd like to know what kind of tool or probe can I use to confirm the orifice size? I just want to be able to confirm for myself. I appreciate any advice. Thanks, Steve Low Pressure Orifice Chart Use a numbered drill set to size the orifices. MTD drill kit. With multiple burners you size and multiply the number of burners for the proper btu's. Remember pressure is also taken and is part of the equation. I must caution you, this is really not a DIY type of project. Is there some reason you can't call the original tech back to verify his work? The One Source For Fittings and Gas Orifices - Anderson Forrester If you want to use a drill bit to check for the correct orifice size, that's reasonable. But calculating the correct input is a lot more complicated, and includes the aerodynamic characteristics of the orifice design as an element, along with elevation of the equipment, BTU content of the gas, specific gravity and other factors. The right way to get the correct burner manifold pressure would be to have all the correct information and to call the manufactures technical services representatives and have them give you the correct burner manifold pressure. For these reasons, setting the burner manifold pressure is not a DIY job. But it may be necessary to find a good repairman to get the correct information and have the correct pressure set. I wouldn't be surprised if that were the basic problem. I wasn't thinking about the manifold pressure, only that the orifice itself was the correct one. I do not want to call the original installer back. Maybe pressure is the problem. After the tech said he changed the orifices over the problem did get better. For some reason the soot is back but not nearly as bad when the unit was first installed. How would the pressure be adjusted? You are right, that is a job I could not handle myself. I guess I should reach out to my propane supplier to check this but honestly I've seen their tech do things that didn't seem right. For example I requested a service last year becasue the boiler would take a while to light. The tech merely blew(with his mouth) the dirt around the elec. pilot. Yes, he solved the problem but only later did I realize how bad the burners were clogged. I ended up cleaning them myself. This also helped the soot problem but did not completely eliminate it. Not sure how he could miss that. Lazy I guess. The burner tubes looked ok. If I do bring in someone to check this what type of serviceman Am I looking for? Dirty burners will cause sooting. Did you take the burners out to empty rust out from the interior of the burners and do a thorough job of cleaning them with a wire brush and perhaps compressed air? The wrong burner manifold pressure will cause to much gas in the burners, causing too rich a fuel mixture, improper combustion, carbon monoxide and soot. A good repairman should have an instrument for measuring the amount of carbon monoxide in the combustion gasses. That would give one indication of whether you have a combustion problem that is producing soot, since soot and carbon monoxide tend to go together in gas furnaces. Unfortunately, finding a really competent repairman can be difficult. Too many service providers have rather marginal repairman up front, hopefully backed up by a competent person to handle problems the front line can't handle, training and such. I was an independent repairman and I did all the work myself. That pretty much meant I had to be pretty good at a minimum. Looking for that independent repair person who does only repairs and does his own work is a strategy worth considering. Also, asking friends, neighbors and relatives for recommendations on competent repairman is worth considering, although that has limitations. Perhaps others will chime in with ideas. Your original post worries me a little bit due to the fact that you have an LP orifice being bigger then NG. The LP gas is stored at higher pressure so it needs to be smaller. When you change anything to run off of NG to LP you need to change out the hoses or pipes as well as the manifold. Most likely your service person did not install a regulator to limit the propane pressure. You will need to check your manual for the correct regulator. Orifice sizing is based upon gas operating pressure and the BTU needed. Equivalent BTU for propane verses natural gas, the propane orifice is always smaller. Standard natural gas pressure delivered is usually 7 inches water column pressure, where as propane operates between 11 and 14 inches water column pressure. However some natural gas appliances such as natural gas lights operate at 4 inches water column. But in this situation the normal standards would be 7 inches natural gas, 14 inches propane. A .129 orifice for natural gas would be about 59000 BTU. whereas this size for propane would be 115000 BTU. The propane orifice size should be .089 (55000 BTU) or .094 (61000 BTU) to rate the same. A .075 propane orifice would be 40000 BTU where as a natural gas one this size would be about 20000 BTU. Most sooting is caused by either improper gas pressure, improper air/gas mixture ratios, or a bad orifice. 7 inches water column is 4 ounces (1/4 PSI) 14 inches water column is 8 ounces (1/2 PSI) Absolute value is that 1 PSI equals 27.7 inches water column
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