My hot water heater supply line runs through the coil in the oil burner so the water is pre-heated some. There is not much room before the water heater to put the expansion tank. Could I place it directly after the hot water heater or if I put it on the supply line before the oil burner will this help with the closed system problem? There is a back-flow preventer installed right after the water meter. Thanks
Another expansion tank dilemma
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Gary Swart
In the Trades
The expansion tank must be in the cold water supply line before it reachs the water heater. Putting it after the heater in the hot water line would not work. In your case, I would put it between the PRV and the oil burner. If there isn't room to put the tank directly under the supply line, tee off the supply line to the side, then elbow down and install the tank. Support it well from above.
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Why does the expansion tank need to be on the cold-water side? Seems to me that unless you had heat traps on the WH, the pressure should be the same on both sides of the WH.
Is it more of an issue of avoiding damaging the rubber diagphragm in the expansion tank?
Is it more of an issue of avoiding damaging the rubber diagphragm in the expansion tank?
Gary Swart
In the Trades
The installation directions specifically say to do it that way. I'm sure some of the more learned professionals can expound the theory behind it, I just follow directions.
hj
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tank
The ideal location is anywhere between the hot water shut off valve and the water heater. But that is just to provide additional protection if the heater supply valve were shut off and the burner/elements turned on and created thermal expansion. It will also function almost anywhere in the cold water system as long as the heater's supply valve is turned on.
The ideal location is anywhere between the hot water shut off valve and the water heater. But that is just to provide additional protection if the heater supply valve were shut off and the burner/elements turned on and created thermal expansion. It will also function almost anywhere in the cold water system as long as the heater's supply valve is turned on.
michaedt
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hot water expands
I'm no expert, that's for sure, but from the perspective of physics, there is a simple reason why the expansion tank must be on the cold water supply line side of the tank instead of the hot side. As the name implies, an expansion tank collects water that has "expanded" during the heating process---that is, cold water expands when it gets hot. If we assume that a system is perfectly insulated, the hot water pipes should already be hot and, therefore, fully expanded (in a perfect world they would be the same temperature as the tank). Therefore, the only place left for the expanding water in the tank is the cold water supply. An expansion tank collects the expanding hot water on the supply side before it exerts any more pressure on the system. As hj said, it protects your system if the shut-off valve is closed or if you have a unidirectional shut-off valve. Again, I'm no expert, but this makes sense to me.
I'm no expert, that's for sure, but from the perspective of physics, there is a simple reason why the expansion tank must be on the cold water supply line side of the tank instead of the hot side. As the name implies, an expansion tank collects water that has "expanded" during the heating process---that is, cold water expands when it gets hot. If we assume that a system is perfectly insulated, the hot water pipes should already be hot and, therefore, fully expanded (in a perfect world they would be the same temperature as the tank). Therefore, the only place left for the expanding water in the tank is the cold water supply. An expansion tank collects the expanding hot water on the supply side before it exerts any more pressure on the system. As hj said, it protects your system if the shut-off valve is closed or if you have a unidirectional shut-off valve. Again, I'm no expert, but this makes sense to me.
The more I think about this, the more I am convinced that the pressure should be the same on both sides of the WH. There is certainly some intuitive logic about the already-hot water on the output side of the WH not being able to expand further, but in the end, the pressure inside the WH from heating the water will push equally on both the hot (output) side and the cold (input) side.
One way of thinking about this is a simple experiment. In the past, before I had an expansion tank, I came to realize that when my pipes started to vibrate loudly at night (from water expansion) I could instantly stop it by opening EITHER a hot or cold tap anywhere in the house. The pressure's the same everywhere, near as I can tell.
Now, I would bet that the reason the expansion tank manufacturers tell us to put them on the cold side is more to do with keeping hot water from weakening the rubber diaphragm, not because they wouldn't work on the hot side.
One way of thinking about this is a simple experiment. In the past, before I had an expansion tank, I came to realize that when my pipes started to vibrate loudly at night (from water expansion) I could instantly stop it by opening EITHER a hot or cold tap anywhere in the house. The pressure's the same everywhere, near as I can tell.
Now, I would bet that the reason the expansion tank manufacturers tell us to put them on the cold side is more to do with keeping hot water from weakening the rubber diaphragm, not because they wouldn't work on the hot side.
Jadnashua
Retired Defense Industry Engineer xxx
Well, the pressure is the same everywhere within the closed system when no valve is open. But, I thought of a couple of other reasons why the cold side is probably better...putting hot water into the tank would mean more energy losses - most of the time, that hot water sitting in that uninsulated tank would cool off, further expanding, and then keep the hot water from reaching the hot water tap after you open it say the next morning - maybe as much as another couple of gallons - that's 48-seconds more cold water in the shower.
Guess you better find a place on the cold side! Course, it would work anywhere, but the other reasons kind of tip the balance. My unprofessional thoughts!
Guess you better find a place on the cold side! Course, it would work anywhere, but the other reasons kind of tip the balance. My unprofessional thoughts!
hj
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pressure
The water in an expansion tank does not go anywhere unless the pressure drops and the air bubble forces it out, but even then it would be in the range of a teacup or less. And the hot water being "expanded" already would make it have less mass and therefore it is lighter, but that has nothing to do with the pressure in the system, which is the same at every point at the same elevation.
The water in an expansion tank does not go anywhere unless the pressure drops and the air bubble forces it out, but even then it would be in the range of a teacup or less. And the hot water being "expanded" already would make it have less mass and therefore it is lighter, but that has nothing to do with the pressure in the system, which is the same at every point at the same elevation.
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What is the outlet pressure?
What is the pressure of the outlet of Hot water tank ff Expansion Tank has air of 40 psi?
It was 40 psi (I forgot.), and it becomes 78 now after I noticed the circulating pump between HBurner and HWTank is broken.
What is the pressure of the outlet of Hot water tank ff Expansion Tank has air of 40 psi?
It was 40 psi (I forgot.), and it becomes 78 now after I noticed the circulating pump between HBurner and HWTank is broken.
Bob NH
In the Trades
The expansion tank should be on the cold supply side so you don't lose as much heat. It also extends the life of the bladder which will deteriorate more quickly if it is hot all the time.
The prescharge pressure in a potable water expansion tank should be the nominal supply pressure. The tank should be empty under normal conditions and will empty when you draw water from the system. There is very little flow to the tank and you don't want it to collect stagnant warm water.
The tank doesn't PREVENT increase in pressure when the water gets hot; it limits the increase in pressure so it won't damage your system.
The prescharge pressure in a potable water expansion tank should be the nominal supply pressure. The tank should be empty under normal conditions and will empty when you draw water from the system. There is very little flow to the tank and you don't want it to collect stagnant warm water.
The tank doesn't PREVENT increase in pressure when the water gets hot; it limits the increase in pressure so it won't damage your system.
Toolaholic
General Contractor Carpenter
maybe ,one more plus for the cold side
long term hot water may affect the rubber bladder,just a guess. Tool
long term hot water may affect the rubber bladder,just a guess. Tool
richardlin
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How to replace circulating pump?
I bought a used CP (circulating pump). It was good when installed, and water was applied to burner. While water presure was increasing, I turned off CP because I was worried that I should add oil to lubricate flange.
After water pressure was balanced at 75 psi, the CP did not work when I turned it on again.
I will take it off to test again. but I just don't know why it does not work now.
Thank you for any input.
I bought a used CP (circulating pump). It was good when installed, and water was applied to burner. While water presure was increasing, I turned off CP because I was worried that I should add oil to lubricate flange.
After water pressure was balanced at 75 psi, the CP did not work when I turned it on again.
I will take it off to test again. but I just don't know why it does not work now.
Thank you for any input.
Bob NH
In the Trades
Did you buy a circulating pump that was designed for 75 psi, or did you buy a circulating pump for a hydronic system that is never supposed to get above 30 psi and is usually 15 to 20 psi?
The bearings and seal in a hydronic system pump may not be made to take the pressure loads from a 75 psi system. The excessive pressure could force the impeller against the housing and prevent the motor from turning the shaft.
A circulating pump for a potable water system should be all bronze because there is always oxygen in the water supply. You can use an iron pump in a hydronic system because the only oxygen is in a small amount of makeup water.
The bearings and seal in a hydronic system pump may not be made to take the pressure loads from a 75 psi system. The excessive pressure could force the impeller against the housing and prevent the motor from turning the shaft.
A circulating pump for a potable water system should be all bronze because there is always oxygen in the water supply. You can use an iron pump in a hydronic system because the only oxygen is in a small amount of makeup water.
richardlin
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Circulating Pump
The circulating pump to be replaced is
B&G HV 102210.
I bought the same one, this time it is a brand new one.
After replacing, I added oil to all three cups and waited for the water to be balanced between input and output of the boiler before turning on pump. This time it works fine although there was some noise from motor before I knocked the motor. It is almost silent this time.
I will test the used one I bought the first time and let you know the result. Probably because I did not wait for water
to be balanced, and broke the flange.
Thank you very much.
The circulating pump to be replaced is
B&G HV 102210.
I bought the same one, this time it is a brand new one.
After replacing, I added oil to all three cups and waited for the water to be balanced between input and output of the boiler before turning on pump. This time it works fine although there was some noise from motor before I knocked the motor. It is almost silent this time.
I will test the used one I bought the first time and let you know the result. Probably because I did not wait for water
to be balanced, and broke the flange.
Thank you very much.
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