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bldginsp
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# Posted: 27 Jan 2017 07:14pm
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Recently bought a Bosch 330 tankless water heater for the cabin. The instructions say that above 2000 feet the gas pressure regulator on the water heater needs to be adjusted from 11 inches water column to 8.5. Having no idea how to accomplish this, I researched it a bit and found out it's really pretty easy and cheap to do. The least expensive gauge for doing this, called a 'manometer', is a simple analog device that costs about $25. Photo below. You fill it with water, hook it up, and read how far the water level is pushed by the gas pressure.
I also plan to get a wall mount direct vent heater, a Williams model. They have different models for different altitudes, but if need be I can easily adjust the pressure.
Apparently it makes a big difference in performance and efficiency to set appliances for the correct pressure at higher altitudes.
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Nate R
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# Posted: 27 Jan 2017 07:24pm
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Just be aware that sometimes the high altitude models have a different gas orifice size entirely, and aren't just working on pressure changes.
Working with gaseous fuels really isn't too bad at all once you understand some of the basic principles, like water manometers, etc.
I spent $10 more and got a dial gauge instead of water manometer for checking pressures in my RV after I replaced the regulator.
Gas pressure is just something most of us don't think about in our daily lives.
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MtnDon
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# Posted: 27 Jan 2017 07:28pm
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Interesting. All the propane appliances I am familiar with reduce the orifice size for higher altitudes and make no changes to pressure.
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bldginsp
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# Posted: 27 Jan 2017 08:32pm
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I guess Bosch figured they could do it this way more easily- or maybe there's a reason they don't want the orifice changed- I'm just guessing. Here's their manual, see page 16.
http://www.bosch-climate.us/files/6720644951-08-IOM-Therm330PN_US.pdf
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MtnDon
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# Posted: 27 Jan 2017 10:22pm
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Yeah, I looked it up before. Not changing the orifice probably means the orifice itself is not serviceable, but is crimp fitted to a larger piece. That is how the orifice in my RV water heater is made. Rather than unscrew the small brass orifice like the fridge or the wall heater, a large formed tube unit has to be changed. The regulators usually have some adjustment anyways so maybe it was slightly less expensive to do the adjustment this way.
This could also explain why Bosch water heaters have a distinct natural gas model and a distinct propane model. Unlike the typical north american gas range that can be changed from one fuel to the other and back.
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bldginsp
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# Posted: 28 Jan 2017 12:36am - Edited by: bldginsp
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Quoting: Nate R Gas pressure is just something most of us don't think about in our daily lives.
That can be a function of my diet over the last 24 hrs.
The instruction manual for the Williams wall heaters has some interesting info. They make models for different altitudes, and I'm guessing there is more to it than orifice size because there are significant price differences. But they go into the whole subject fairly extensively, even describing a method of measuring btu input for natural gas (but not propane). For propane, they just say that if your propane is not the standard 2500 btus per cubic foot you should contact your local gas supplier for correct orifice size.
They also tell you how to measure the manifold pressure, but give you no means of adjusting it if it's off, since the furnace has no regulator like the Bosch. They do, however, clearly specify an input pressure of 10 inches water column at least, no more than 13, and that manifold pressure should be 10. So I suppose it's best to verify all this at startup and adjust the pressure at the supply tank regulator if necessary, as Nate did when he got a new regulator on his RV. I guess it's really just a double check to make sure something isn't radically off, or off enough to cause less efficient burning. The Willams manual gives a very detailed description of the shape and color of properly burning flames, as another means of verifying proper burn characteristics.
Three factors can change the air/gas proportions- altitude which will cause oxygen content of air to vary with height, pressure setting at the supply, and length/diameter of supply pipe which can reduce operating pressure because of flow resistance. Even if the supply delivers 10 in water column you might have less at the appliance due to pipe resistance. So I suppose it's a good idea to check manifold pressure under operation with other appliances on the same piping system operating simultaneously. Maybe I'm overthinking this.
http://www.williamscomfortprod.com/wp-content/uploads/2016/03/DIRECT-VENT-r-3-21-2016 P322101.pdf
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