Puzzled-- the numbers don't add up!!!

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  #1  
Old 11-07-18, 10:13 AM
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Puzzled-- the numbers don't add up!!!

Hi! I installed a new oil heat system last winter-- new boiler, new fuel oil tank. My question concerns the fuel tank. I bought what I thought was a standard 275 gallon fuel tank (and it certainly has the dimensions of a standard 275 gallon tank: width, 60 inches, height 44 inches, depth 27 inches), but it doesn't have anything close to a 275 gallon capacity. When it was-- presumably-- completely empty and being filled for the very first time, it took 237 gallons. And every time last winter that I filled it when it already had some oil in it, the amount it took was commensurately less than 237 gallon. So although I obviously can cope with whatever its actual capacity is, I would like to understand why this is happening. I have a few hypotheses, but I'm too unschooled in the realm of fuel oil storage tanks to speculate intelligently-- and so I turned to the folks here at DIY for an informed answer.

Oh, one other question: Does it matter whether the boiler is on or off during the actual oil delivery?
 
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  #2  
Old 11-07-18, 10:38 AM
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Welcome to the forums.

There should be an ID tag on the tank. The capacity will be on it. Typically the fuel oil is drawn from the top of the tank. There is a tube that goes down into the tank but does not go all the way to the bottom. There is always some oil left at the bottom of the tank even when the gauge shows empty. The gauge is usually setup so that it shows empty when the oil level is at the suction tube.

I would always shut my oil burner off for several hours after a tank refill to allow any sediment to settle back down to the the bottom of the tank.
 
  #3  
Old 11-07-18, 11:20 AM
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Additionally, many tanks have vent whistles, which make noise during a fuel delivery until the oil level reaches the whistle. On my tank, the whistle extends several inches down into the tank. The delivery driver will stop filling when the oil reaches that level, and I will (should) never have oil to the very top of the tank.
 
  #4  
Old 11-07-18, 07:58 PM
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With those dimensions that you gave you are suppose to have a 275 gal. tank. They never fill to the top because of a whistle that's installed to let the oil man know when it's full. The whistles come a certain length and how you cut them determines how full your tank gets.

The longer the whistle the less oil you get.

You can google oil tank dimensions to see the different options.

Hope this helps a little.
 

Last edited by spott; 11-07-18 at 08:40 PM.
  #5  
Old 11-07-18, 08:04 PM
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Hi! Thank you PJMax and SuperSquirrel for your responses to my questions.

PJMax, my oil tank supplies the boiler from the bottom, so I imagine the very sound logic you apply to your own top-supplying tank about letting the sediment settle for a couple of hours wouldn't apply to my situation. Is that right?

Super Squirrel: regarding the 237 gallons--which was all I got the very first time I filled it, when the tank was newly purchased and I assume empty-- could such a large gap (275-237=38 gallons) be created by the way that vent whistle works?

PJMax, I wasn't notified that I got responses to my question. Would you be kind enough to tell me what I have to do to be notified by email?
 

Last edited by PJmax; 11-08-18 at 12:55 AM. Reason: reset notification
  #6  
Old 11-07-18, 08:08 PM
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Spott, I just saw your reply. Are you sure about the fact that with those dimensions it's only 250. This morning, I googled 'standard size of fuel tank for a home' and they said 275 gallons was the standard size and they gave those dimensions as that of the 275 gallon tank. Then I went to my basement and measured my tank and got 60x44x27 inches, the very numbers I had just gotten when googling the question!
 
  #7  
Old 11-07-18, 09:19 PM
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You do have a 275 gal. Post #4. At first I thought it was a 250 but deleted it. I don't see it here now.
 
  #8  
Old 11-07-18, 09:53 PM
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I know there's math to determine the volume of a curved vessel, but I'm lazy, so I'll use this chart for reference, and hope it's accurate : Tank Chart for Measuring Your Residential Heating Oil

I don't recall the exact length of the vent whistle, and like Spott said, they could vary. I'd estimate my vent whistle is about 6-8 inches inside the tank. So 6 inches takes a 44 inch tall tank down to 38 inches of fuel. Per the chart, filled to 38 inches, you're at 248 gallons. If it was an 8 inch whistle, that leaves you with 235 gallons of fuel. So basically spot on for the delivery amount you received in your new, empty tank. Combined with some residuals you will have on your subsequent fills, like PJ said, you would need even less to "fill it up." And even with a bottom supplying tank like yours (and mine), there's probably a little bit that doesn't make it to the valve. Which is actually good, because that last dribble probably has the worst sediment in it.
 
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Old 11-08-18, 12:52 AM
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Even if the tank is fed from the bottom..... there should be a stub up into the oil. Oil should not be drawn directly off the bottom of the tank.

You had checked "weekly email notification" for this thread. I changed it to instant for you.
To check the notification..... go to the "Go Advanced" editor mode.... and scroll down below the reply box.
 
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Old 11-08-18, 02:23 PM
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SuperSquirrel says, "I know there's math to determine the volume of a curved vessel, but I'm lazy, so I'll use this chart for reference, and hope it's accurate "

Hey, SuperSquirrel, it isn't laziness that would stop a person from using integral calculus to determine the volume of a curved vessel without even knowing the equation describing the exact curve in question, it's simply commendable good sense in avoiding the pointless expenditure of blood, sweat and tears! And your blood, sweat, and tears strike me as particularly precious, SuperSquirrel!

By the way, SuperSquirrel, should I assume that you went into your basement and removed some sort of cap from your fuel tank, and peered inside with a flashlight to determine the approximate location of your vent whistle?

PJMax says, "Even if the tank is fed from the bottom..... there should be a stub up into the oil. Oil should not be drawn directly off the bottom of the tank."

Interesting and reassuring, PJMax! I had been concerned about drawing gucky sediment into my boiler, and I'm glad to know of the presence of that 'stub' to prevent that!

And, PJMax, thanks for adjusting the notification setting for this thread. I've just made that adjustment for all threads.
 
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Old 11-08-18, 03:16 PM
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You're welcome..... your wish is my command.
 
  #12  
Old 11-08-18, 05:53 PM
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PJ, thanks for coming up with the term "stub." I wanted to convey that idea last night, but the words just weren't there for it to happen.

EverLessInept, I was there when the new tank was installed a few years ago, so I happened to see the vent alarm before it was installed into the tank.
 
  #13  
Old 11-09-18, 01:49 PM
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SuperSquirrel, I'm just curious: have your new fuel tank fill-ups since your purchase borne out your sense of the location of the vent whistle? In other words, has it strengthened the likelihood that your tank's real-world capacity is somewhere between 235 and 248 gallons (depending on the vent whistle's being either eight inches or six inches from the top, respectively)?

Now, it's quite possible that you have a contract with a particular fuel supplier and they make deliveries based on their estimates of your need and therefore you haven't followed especially closely how low your tank's level was just before a delivery was made. I'd certainly understand that.

My situation, however, is very different. I've chosen to not have a contract with a particular supplier; instead I use a 'market', where a few different suppliers in my area make bids for my business, offering to sell me X amount at this price, or Y amount at that price-- some of them give discounts (and pretty big ones, too) for cash transactions while others don't. Since I have to take the initiative each time I need oil, I must be very cognizant of my oil tank's level. So, for example, on Wednesday I saw that my tank was about 20% full, and I arranged a next-day delivery. They filled it up, and managed to do so with only 190.1 gallons. So if you do the math, my tank when empty took 237.3 gallons, and 190.1/237.3 is 80.1%, so my estimate that it had only about 20% remaining when I made the order was quite on the mark.

SuperSquirrel, have you ever made a comparable estimate of the % of oil that remained in your tank just before a delivery and then had your inferences regarding your tank's practical capacity (based on the vent whistle location) corroborated when you saw the bill and noted how much oil had been necessary to fill up the tank?
 
  #14  
Old 11-09-18, 06:57 PM
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I'm on an automatic delivery plan, so the oil company comes when they estimate I need it. However, I still keep an eye on the gauge, especially when I haven't seen the oil truck in a while. That way, I can poke them to make sure I have a delivery coming and I don't run out. My threshold to poke them is 1/4 tank.

Last winter, I got down to just below 1/4 tank on the gauge. Looking at my records, that delivery was 189 gallons. Now, the tank gauge is only marked in increments of Full, 3/4, 1/2, 1/4, and Uh-oh. I will assume that the tank gauge is calibrated to the the useful capacity of the tank, being 275-g, where g=the dead space, in gallons, accounted for by the size of the vent whistle. The gauge always reads completely full after a "fill-up." If it were calibrated to the nominal capacity of 275 gallons, then it would never read as full, due to the dead space.

If that's the case, then if I was at 1/4 tank, or 0.25, and I received a 189 gallon fill, then the capacity of the tank is... well, since you threw down math first... Solve for x, with x being the capacity when the tank reads full.

0.25x + 189 = x
Multiply by 100 to get 25x + 18900 =100x
Subtract 25x to get 18900 = 75x
Divide by 75
252 = x

Which corresponds on the chart with between 38 and 39 inches, so let's say 38.5, and 44-38.5=5.5, which is quite close to my estimate of 6 inches for the vent whistle. Given the relative imprecision of the gauge, and the fact that it actually read a wee bit below 1/4 tank, I think a valid working assumption is that the vent whistle extends approximately 6 inches into the tank, and the useful capacity of my tank is approximately (and probably slight less than) 250 gallons.

That's the only delivery where I can remember a specific level that it got to. Most of my deliveries come at or before the 1/2 mark, and run between 100-120 gallons. If I'm at 1/2-ish, and they put in 120-ish, that's close-ish to the 250 as well. But I just don't monitor it that closely when I know I still have a half tank left. Though I suppose, out of morbid curiosity, I may just watch the thing like a hawk now.
 
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Old 11-10-18, 03:04 PM
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SuperSquirrel says, "[size=3]I'm on an automatic delivery plan, so the oil company comes when they estimate I need it. However, I still keep an eye on the gauge, especially when I haven't seen the oil truck in a while. That way, I can poke them to make sure I have a delivery coming and I don't run out. My threshold to poke them is 1/4 tank.”[/size]

Given the fact that you have a (presumably) fairly long-standing relationship with the oil company-- which, I imagine, you determined to be an ethical and responsible one before you even signed the contract with them for the first time-- you justifiably expect that even the gentlest poke from you (equivalent to a mere tickle in the ribs, as you might do to an infant!) will make them jump to immediate action.

Lacking that enviable set-up myself, I wanted to maintain control of my own fate regarding oil deliveries, perhaps subconsciously bearing in mind the calamitous chain of events that once befell oil heat users in NYC, events that are recalled by grizzled veterans of that episode with an involuntarily grimace and pained grunt at the mere recollection. In fact, this true-life horror tale is sure to be recounted by its 'survivors'-- too melodramatic a word? not necessarily!-- to their grandchildren in lieu of a bedtime story at least once! (And knowing how children are, more likely a dozen times!)

Granted this incident’s having happened at all was odd, unlikely, and requiring several quirky twists of fate--nevertheless, it’s not necessarily unique and unrepeatable.

It originated in a surprise snowstorm-- as much a surprise to the New York Sanitation Department (responsible for dealing with snowstorms and marshaling the appropriate manpower in advance), and the National Weather Service (then, rather quaintly, called the Weather Bureau and still in the early, primitive years of computer forecasting) as it was a total shock to the ordinary citizen. A storm that was expected to drop a couple of inches of snow before turning into a harmless rainstorm defied the laws of meteorology as they were then understood and ultimately deposited well over 15 inches in Manhattan and twice that in the outer boroughs. So, yes, everyone was caught off guard.

But even more crucial-- and catastrophic!-- to the unprecedented outcome was the fact that it occurred on a Sunday-- when the Sanitation Department workers were all at home, smoking cigars and watching football-- which meant that the storm got even further ahead of them than it would have if it had occurred any other day of the week, even Saturday. Sure, the workers were eventually called at home and told to report on an emergency basis-- but what does it mean when virtually no snow plows or salt-spreaders are on the streets of New York City for the first 10 inches of a blizzard? It means of course that eventually cars get stuck in the accumulated snow-- they can’t move forward or back-- and remember, a single such stranded car in one location soon means dozens, then hundreds simply because of that first one… And at a certain point-- most likely when night falls-- even the most conscientious driver is going to feel compelled to just abandon his vehicle.

Vast numbers of cars were thus left deserted by their owners. How many? Here’s one gauge: about a thousand vehicles were abandoned on the old Tappan Zee Bridge alone!! That bridge is 3 miles long. New York City (not including the suburbs) has 6074 miles of road. Granted the actual calculation-- because of unequal distribution of vehicles-- is much more complicated than simply dividing 6074 by 3 and multiplying by a thousand. But SuperSquirrel, I have great faith in your ability--in your last post you showed signs of being quite capable of proving the Riemann Hypothesis in a half-hour’s time if you were so inclined-- to do the math.

So as Sunday turned into Monday, picture countless empty, abandoned cars clogging virtually every street of the city! And now think of how complicated and time-consuming the logistics must inevitably be to bring a happy ending to this real-life Rubik’s Cube-- not a Rubik’s Cube with a mere 27 movable parts but tens of thousands of immovable parts !

And finally, imagine the effect upon all the oil heat users in New York City due for a fuel delivery on Monday or Tuesday. And badly overdue for a delivery by Wednesday. And without heat by Thursday! So if even a Volkswagen Beetle couldn’t maneuver through the streets for days, imagine a giant oil delivery truck trying to! And bear in mind that it was February in New York! Bitterly cold temps and no melting courtesy of Mother Nature, who definitely didn’t ‘temper the wind to the shorn lamb’, as the expression goes. And New York City certainly was shorn that February, baby!

And now a grandfather telling his grandchildren about this-- the ‘Lindsay snowstorm’ (named in anger for the mayor who never contingency-planned for this worst case scenario snowstorm)-- will suddenly become the protagonist of his own bedtime story, because he-- like people all over the city who were living in large apartment buildings without heat for days-- was forced to become a Nanook of the North and join with his fellow apartment-dwellers to dig out all the cars on their street. And understand, SuperSquirrel, how remarkable this is: New Yorkers, not a very sociable bunch in the best of circumstances (I can say this, as a New Yorker myself!) managed to rise to the occasion in this worst of circumstances and self-organize this collective shoveling action in the pre-personal computer age, when ‘flash mobs’ were still forty years in the future!

So eventually the fuel oil trucks got through, heat was restored and the populace rejoiced-- but not without spending days with numb fingers and red noses in heatless oil-heated apartments all over the city! (And in those days most apartment building were oil-heated.)

SuperSquirrel, given my temperament-- I have deeply-ingrained awfulizing tendencies, where I automatically foresee every horrific consequence possible and my imagination has me tangibly experiencing those consequences even without their actually occurring!-- I would never let my oil supply drop low enough to permit only a few days of heat. That’s why I like maintaining complete personal control of my tank’s resupply.
 

Last edited by EverLessInept; 11-10-18 at 03:05 PM. Reason: typo
  #16  
Old 11-10-18, 05:54 PM
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You greatly overestimate my relationship with my oil company. It's more akin to that of a parent and child. The child says he will clean his room, but will he really? Trust, but verify. I trust them to do what they say they will, but assume they they won't, at least not without some gentle nudging, some exasperated sighing, and plenty of eye-rolling. When prodded, they move with the alacrity of a sloth, but oil does show up within a few days. With the automatic delivery, if they manage to do it in time without prodding, then at least it's one less aggravation in my day. I can't imagine never checking, or having a way to check, the tank level on my own. Now, they say if I am on automatic delivery and actually run out, they'll compensate me, but compensation after the fact won't keep me warm in the here-and-now.

That 189 gallon fill-up was 64 days from the previous one. Having used 2.95 gallons per day in that time, and assuming a continued usage at the same rate, I had roughly 20 days' worth of fuel remaining when I was topped off again. Of course, we don't want to be slurping the sludgy goodness at the bottom of the tank, and there will always be an inaccessible, unusable amount left anyway. I felt comfortable that they would get me fuel in time, but I really wouldn't ever wish to push my luck much further. At least living where I live now, I'm not down a disused side street that the snow plows take one glance at and drive past. We were so used to being forgotten that we didn't have to wait for desperation to set in. When the snow stopped, we started shoveling the entire street. Otherwise, in a few days to a week, the city would send a skid-steer to start working on digging us out (usually ripping up a few parked cars in the process).

And of course dividing 6,074 by 3 and multiplying by 1,000 won't work, and not simply due to uneven distribution of vehicles. It totally fails to take into account the lane-miles (that is, the length of the roadway multiplied by the number of lanes on that roadway). The number of lane-miles upon which cars may be stranded in NYC totals over 19,000. But who's counting.
 
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