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(2) 275 gallon heating oil tanks questions?

jamoka3jamoka3 Member Posts: 3
New to the forum, and new to owning a home with heating oil tanks.
Have a few questions...
(See attached pic.) Is the tank on the left which has my fill pipe attached supposed to be more full then the tank on the right? The right tank has the vent pipe. The left tank is about 4 inches from the top, I pulled the center plug to see, and the right tanks about 14" lower...
Curious to know, because the right tank has my fuel gauge and its never above 3/4 full even when its topped off. So I assume the left tank is my "main" fill tank and the right tank is the secondary tank?
Both valves seem open on the bottom . And they both tie into the same feed pipe under the tanks to the boiler.


  • Intplm.Intplm. Member Posts: 1,129
    Yes @jamoka3 . The left hand tank in the picture will fill a bit more because it has the fill pipe directly piped to it.
    The way these tanks are twinned together will make the vent whistle / vent alarm stop a little early. Leaving the tank with the vent attached with less oil.
    In some areas this piping arrangement is no longer allowed by code. The new codes would have each tank piped with a separate fill and a seperate vent.
    Your piping arrangement looks fine however and should not pose any other concerns.
  • HVACNUTHVACNUT Member Posts: 3,265
    In addition to what @Intplm. said, the levels between the tanks should equalize after a while from the crossover on the oil lines. It's not uncommon for the crossover to get clogged. But that usually leaves one tank full and one tank empty.
    And unless someone has the same exact basement and oil tanks, you've posted that pic here in the past.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,927
    Don't know what your looking for. This has been asked and answered as those tanks were posted on here previously
  • STEVEusaPASTEVEusaPA Member Posts: 4,103

    Don't know what your looking for. This has been asked and answered as those tanks were posted on here previously

    I thought they looked familiar. They are still allowed by code to pipe with a crossover. What is needed are swing joints on the supply and vent piping. And proper spacing.

  • jamoka3jamoka3 Member Posts: 3
    This is the first time I asked this question... and yes i have posted this pic Before. This pic was saved on my phone and was the best one to show my tank layout.
    That was the first time i ever posted, and asked what size tanks they may have been, since they are painted over and there where no identification tags with tank capacity.
  • STEVEusaPASTEVEusaPA Member Posts: 4,103
    With the tanks piped in series your situation is pretty common.
    Most likely with 2 tanks, the delivery driver is filling at high speed, and the crossover is causing foaming, which is stopping the whistle sooner. Slower filling may get a little more in the tanks.
    You also have to leave room for expansion especially in the dead of winter when you get a 20 degree temperature oil fill into your tank and it warms up to 60-65 degrees.
  • ronron Member Posts: 143
    from that pic the piping setup is clean and about as minimal as it can be. During a fill of an oil tank there's the audible whistle thing that howles during fill and when the tank fills to about 85% the oil reaches the whistle straw and the whistling stops. When the oil guy outside is filling he [microaggression] only pumps oil while hearing the whistle and stops when the whistling stops. Otherwise he would never know when the tank is full and when to stop pumping (and fill your basement with oil)

    with the fill pipe only going to one tank the only way oil gets to the other tank is via the 3/8" crossover pipe on the bottom and for a typical one tank fill of ~200 gallon, the fill tank will fill normally while the other tank will remain at the same level during the 5-10 minutes it take the oil guy to fill [the one tank]. And then it would probably take a couple hours for the oil to equalize via gravity though the bottom 3/8" crossover between the 2 tanks, guesstimating a 1gpm flow rate through the 3/8" line.

    A 275 gallon sized tank holds ~250 gallons oil (remainder is air space). If both tanks on E are at 20 gallons left, then the fill tank will get full to 250 gallons while the other tank is going to stay very near 20 gallons during fill time. After a few hours both tanks will equalize to 135 gallons. Not ideal if you run both tanks to empty you would need repeat fills however many times to get both tanks above 3/4. But if you are on a monthly oil delivery then it is kinda peace of mind having the capability of having more than 250 gallons at one time but you would likely never get above 3/4 full after tank equalization (as you've noticed).

    And you're probably never getting very far over the single tank capacity of 250 gallons.

    to get max capacity out of both tanks you would need the fills separate, as well as the vents and functioning whistles so the fill guy knows when a given tank is full. that would require punching 2 more holes through your foundation.

    if you want/need more oil capacity the best solution is usually a new single tank. Your current shape 275 gal also comes in 330 gal. being an extended length. But you can get single tanks larger than 330 gal. Your two 275 gal tank setup is kind of a poor man's way of getting more than 275 gallons without piping a separate fill/vent through the foundation.

    I know Roth makes a 400 gal. rectangular tank that's 30" wide.
    those two 275 gal tanks are eating up more space than they are holding liquid oil. if it were me and I wanted the basement space i wouldn't think twice about removing one of those tanks and going with a single 275 gal tank... knowing it would fill to full and be 250 gallons and then u can work out your usage rate and how often to expect a required fill.
  • HVACNUTHVACNUT Member Posts: 3,265
    @Ron you need to read all the posts, not just the first one. I know we get a little drab sometimes, but there's some good info up there. 😘
  • STEVEusaPASTEVEusaPA Member Posts: 4,103
    DANGER! DANGER! Please make sure you have those plugs you removed doped and re-tightened on those tanks, especially the left tank.
    The whistle won't stop (might not even much noise).
    Your insurance company won't pay a claim on it and put all the liability on you. And probably the oil company's insurance won't pay either if you touched it.

    We had a thread before about a guy who was really really obsessed(?) with wanting to know exactly how much oil was in the tank.
    Think of that oil gauge like your car gauge. You have to figure out what 'full' is and what 'empty' is. The gauge is more like a pretty good indicator.

    Easiest is to deal with an oil company who will put you on automatic delivery, track you usage, fill your tanks. Simply done by getting 2 complete fill ups, and putting the required info into a computer to calculate fuel usage basically the same way you track MPG in your car--fill up, drive so many miles, fill up, do some simple math.

    I have hundreds of oil customers on auto delivery and they never run out. And they get a better price as I can forecast and schedule deliveries their deliveries more efficiently.
  • STEVEusaPASTEVEusaPA Member Posts: 4,103
    @ron I think you do not fully understand how the crossover works.
    The tank on the left is connected to the fill, the tank on the right has the whistle and vent.
    The tank on the left fills completely up then the oil is pushed via the crossover into the tank on the right. The whistle blows the entire time.
    When the tank on the right gets about 7/8's full the whistle stops.
    So tank on the left, full 275 gallons, tank on the right about 240 (if filled fast) to 250 gallons.
    Settled out total volume will be around 500 gallons.
    Separate fills wouldn't increase the total volume as now both tanks will end up with about 240/250 gallons each.

    I personally don't like this set up, even though it's allowed by code, and at minimum I will always do 2 fills, and one connected vent.

    Either way they are piped, best to draw them both down together, and fill them together. Trying to work off one or the other, and you'll probably end up running one dry and will have to re-prime the system. And it will probably happen right after you left for the weekend...yikes!
  • Alan WelchAlan Welch Member Posts: 206
    Unless you just had a delivery , both tanks should be equal. Even the crossover pipe should have swing joints as well.
  • ronron Member Posts: 143
    i call the "crossover" the 3/8" line at the bottom.

    i would call the 2" pipe connecting both tanks at the top the vent crossover which does not transfer oil but is needed to make a single whistle and a single vent pipe to outside work.

    anytime tanks like this are filled once, they settle out at 175 gallon in both tanks thus never more than 3/4 on the fill gauge (unless u look within one hour after filling and if gauge is on the filling tank).

    my point is with the 3/8" crossover line at the bottom, which is the only way oil can get from the fill tank to the secondary tank, oil is not pushed during fill. Not with a functioning vent. The transfer of oil through it is done completely by gravity by weight and height of the oil in the fill tank. The pressure of filling will not force oil any faster through the 3/8" line to fill the secondary tank so during the 5-10 min fill time to put 150-200 gallons in one tank, the secondary tank is not going to increase by more than a 1-2 gallons. It will take hours for the oil to make it through that 3/8" line at the bottom and for the level in the secondary tank to rise. which is the major drawback of that piping setup...

    having 2 x 275 gallon tanks which realistically can only hold 250 gallons liquid oil each for a total of 500 gallons... the reality is the oil truck comes once and your ending up with a total of 350 gallons of oil once equalized.

    - both tanks at 100 gal
    - [fill #1] put fill tank to Full @ 250 gal
    - equalizes hours later to 175 gal between the two
    - [fill #2] put fill tank to Full @ 250 gal
    - equalize hours later @ 212 gal (175+250 / 2)
    - fill # 3, equalize to 231 gal (212+250 / 2)
    - fill # 4, equalize to 240 gal (and so on)
    - fill # 5, equalize to 245 gal
    - fill # 6, equalize to 247 gal
    - fill # 7, equalize to 248.8 gal
    - fill # 8, equalize to 249.4 gal
    - fill # 9, equalize to 249.7 gal

    you would need 3 fills if not 4, each happening the day after with no significant oil use over that time, to get both tanks near full and get the gauge over 3/4 to F.

  • Alan WelchAlan Welch Member Posts: 206
    Ron, to be blunt, your wrong .The oil gets filled into the tank closest to the wall. Any air gets pushed into the second tank. when the first tank is full the oil goes through the 2 inch pipe into the second tank. when the oil in that tank reaches the stem on the whistle vent, the whistle stops. the 1/2 inch or 3/8 inch line beneath the tank is the equalizing line . if the tanks are not equal the day after a delivery, either the equalizing line is blocked or a valve is closed.
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