Question about natural gas boiler


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Old 04-11-09, 09:05 AM
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Question about natural gas boiler

My friend has a Weil-McLain boiler that only does his baseboard heat, no hot water. It is just one heating zone, and it is 1" copper. The pressure/temp gauge on the pipe varies between ~32 and ~38 psi. There is also one of those 12-15 psi Watts regulators. Is that pressure normal for 1" pipe? Someone must have internally increased the regulator, correct?
 
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Old 04-11-09, 09:52 AM
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Boiler Pressure

Are you sure he's reading the gauge correctly. Some gauges are calibrated in "feet". One PSI = 2.3 feet of water column so 15 PSI would equal 34.5 feet of water column.
 
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Old 04-11-09, 09:52 AM
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Not normal... if the gauge is accurate (I hate gauges!) it suggests that there is a problem with the Safety Pressure Relief Valve and could be a dangerous situation.

Someone must have internally increased the regulator, correct?
Not necessarily... there could be several things wrong, or a combination of problems.

1. Verify the gauge accuracy. Without knowing the TRUE pressure, yer shooting in the dark without night vision.

2. If the pressure relief valve is more than 5 years old, replace it. Relief valves on boilers should be 30 PSI units, and that one should have opened if in fact the pressure IS above 30.

3. Check/adjust the expansion tank. Verify air charge is correct if it's a bladder tank, or drain if a compression tank.

4. Verify correct operation of the pressure reducing valve.

5. If the system also supplies domestic hot water via a 'tankless' coil, verify that it is not leaking and pressurizing the boiler.
 
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Old 04-11-09, 09:54 AM
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Yep... I bet that's it Grady!
 
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Old 04-11-09, 10:13 AM
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I'll check the gauge units, thanks.
 
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Old 04-15-09, 09:10 AM
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I checked the gauge and it is in fact psi, not feet of water. There is no domestic water so the tankless coil thing is not an issue. There is however this tank hanging from the celing (could this be the expansion tank you speak of?). It looks like it would hold about 6 to 7 gallons of water. It is cylindrical and strapped horizontally to the ceiling. It doesn't look like the expansion tank that I have (classic expansion tank with the air fitting on the bottom). One final question, does the pressure need to be higher in 1" pipe, or is 15-20 standard for both 3/4" and 1"?
 
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Old 04-15-09, 01:41 PM
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pressure has nothing to do with pipe diameter.
The pressure needed in enough to push the water up the entire height of the building.
15 psi is probably enough for maybe 20 feet of height of water, measuring from bottom of boiler to top of highest radiator (there are tables you can look this up for more precision) but if its only one floor, you have way more than you need.
 
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Old 04-15-09, 02:10 PM
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Originally Posted by msgale
The pressure needed in enough to push the water up the entire height of the building.
Not quite the way it works... the pressure isn't needed to "push" water anywhere. The pressure simply decreases as you rise (1 psi for every 2.3') and you typically want at least 5 psi at your highest point so that you can bleed any air rather than introduce air if you have a low pressure situation.
 
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Old 04-15-09, 04:04 PM
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Yet another way to think of the pressure... is the inverse of what Who posted (1 PSI per 2.31 FT) ... is 0.433 PSI per FT ...

So, if you had a vertical pipe of ANY diameter, 1" or 10' it doesn't matter... say 20' tall, with a pressure gauge at the bottom of that pipe, you would see 8.66 PSI on that gauge.

Another reason for the couple extra PSI is to give a little extra pressure to avoid having hot water flashing to steam... and... if your circulating pump is set up such that it's pumping toward the expansion tank, rather than away from it, when that pump turns on, it will LOWER the pressure in the system...
 
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Old 04-15-09, 06:32 PM
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Tank

If the tank has a cap & tire valve (usually on the opposite end from where the pipe attaches) it is a bladder type tank. You need to shut off the water to the reducing (feed) valve, drop the boiler pressure to zero (good chance to check the gauge) & check the pressure on the tank with a tire gauge.
 
 

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