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Thread: Expansion Tank

  1. #1
    DIY Junior Member
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    Default Expansion Tank

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    We have an older fuel oil boiler, approx 15-20 years old. Its a 1800 square foot home.

    So i have a couple of questions. We are using about 5 gallons of fuel oil a day and we don't keep it warm its only like 68. While outside temp has been around 5 degrees.

    We purchased the house during the summer and did have the boiler serviced before winter. We did run into some problems with the expansion tank getting water logged its one of those huge barrels hanging in the joists. No matter what i did it will just get over 30psi and start to blow off from the relief valve. So i just turned off the water to the boiler so extra water couldnt get in. The water temp on the boiler doesnt get higher than 180f and the water pressure is right around 20 psi now. Do you think that i lowered the efficency of the boiler by not letting in enough water into the system.

    I have tried several times of draining the tank and refilling it. It also has one of those atrol things attached to the tank, i have heard those are awful and are hard to fine tune.

    Would it be worth just buying a #60 expansion tank with the bladder inside, turn off the valve to the old tank switch it and call it a day? Do i need anything else with the new kind of expansion tanks? Are the air seperators required?

  2. #2
    Previous member
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    Lets start at the beginning. the water pressure has zero effect on boiler efficiency or fuel usage. Replacing your tank will not make a difference although, draining it will solve the pressure problem. Water expands when you heat it and it needs a place to expand to. If there is no air cushion in the tank, the water has no place to go other than out the relief valve. If the house will not heat and you had the boiler serviced recently there is a chance that the technician put a nozzle in the burner that is too small. 180 degree water is plenty hot enough, though you could jack it up to 200 if the boiler is fired at maximum.

  3. #3
    DIY Junior Member
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    its not that its not heating the house it just seems like it went through alot of fuel oil. 100 gallons in 20 days... i guess we should more look at our insulation than anything? i was just concered that it was the boiler

  4. #4
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by bigal0043 View Post
    its not that its not heating the house it just seems like it went through alot of fuel oil. 100 gallons in 20 days... i guess we should more look at our insulation than anything? i was just concered that it was the boiler
    Your boiler is probably only running about 60% efficient so for every 100 gallons you put in it you're only getting 60 gallons of heat out of it.

    This would be my guess anyway (and 60% eff. could be on the high side).

  5. #5
    DIY Senior Member wallygater's Avatar
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    Default expansion tank

    Should the expansion tank have no water in it?
    My friends tank is full. Should he drain it?
    How often should this tank be drained?
    His pressure is way to high and water is coming out of the release valve on the water heater.
    wally

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    There are two general types of expansion tanks. The 'original' older style is just a plain tank. These have no separation between the water and the air, and over time, the air gets absorbed into the water. Those, you need to purge of water periodically. This is also tough on the plumbing, since the air contains some oxygen. That allows things to rust or corrode much more than the newer type. The newer type has a waterproof bladder that separates the air and the water. When the bladder fails, the whole tank fills up with water and it must be replaced. If the bladder is intact, if the Schrader valve leaks, it could lose its air charge (think tire pressure). If that happens, same thing - no room for the water to expand.

    To set the pressure on a bladder tank, you must first remove any water pressure on it. then you pump it up like a tire to about the same pressure as the system's normal operating pressure. They often come precharged to 14# or so, which is fine for most systems. You should always check before installation and adjust to your conditions first.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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