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Sludge & crud or contaminants in heating oil storage tanks:
This article explains the causes and cures for heating system problems due to sludge in home heating oil tanks, including problems of clogged oil piping, clogged oil filters, oil burner malfunctions, and loss of heat due to sludge in the oil tank. We explain why sludge is a problem in home heating oil & why it leads to loss of heat.
We give first aid advice for what to do if you ran out of heating oil and want to avoid stirring up sludge when oil is delivered.
We continue with all of the methods used to avoid sludge problems in heating oil storage tanks: blowing out a clogged oil line, using additives to break up oil tank sludge, installing a Scully Snorkel® to avoid picking up oil tank sludge & water, improvements in oil line filter capacity, steam cleaning oil tanks & lines, & oil tank replacement options.
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When we serviced heating equipment in the early 1970's, we often found oil fired heating boilers or furnaces that had worked ok for years without any oil filter installed whatsoever!
We were amazed until we learned the history of heating oil cleanliness. We're not talking about the number of BTU's per gallon of heating oil, just how clean or dirty it is.
[Click to enlarge any image]
Before the 1970's oil crisis when much of the heating oil sold in the U.S. was from the middle east, if you put some heating oil in a bottle and examined it, it was a lovely clear yellow color, much like cooking oil. Currently (2008) heating oil in most of the U.S. is black goopy stuff with lots of large molecules that tend to settle out as black sludge in an oil tank, heating oil line, or oil filter.
Heating oil companies are not to blame for this messy stuff. Heating oil is being produced by "cold cracking" - it is chilled and centrifuged rather than distilled into clear oil as in the "old days".
A result of this change in heating oil manufacture is that even overnight in a heating oil delivery truck, a driver may see evidence that some components of heating oil in the tank are settling out as sludge material. The same thing happens in a home heating oil tank. What problems does sludge in an oil tank cause?
The Times article also noted that beginning in 2011 New York instituted the "NYC Clean Heat" program by adopting new regulations to phase out the use of No. 4 and No. 6 heating oils that emit soot and reduce air quality. The NYC Clean Heat program coordinates oil companies, banks, environmental groups and property owners to provide financing intended to help property owners switch to use of cleaner heating fuels like natural gas or low sulfur No. 2 heating oil or biodiesel. 
11 Feb 2015 Anonymous said:
what causes sludge in heating oil tanks
Good question Anon.
Before the U.S. was mad at Iran (and vice versa) on the East Coast at least, much heating oil came from that part of the world and was stunningly clean - it looked like yellow cooking oil. Currently a lot of No. 2 home heating oil is being refined from other oil sources and the oil looks ugly even when fresh in a jar - more black, containing more ... well I dunno, "crud" or more properly "residual hydrocarbon waste" ... even if it has about the same BTU value per gallon.
Oil tank sludge (for home heating oil) is comprised of about 90% hydrocarbon waste, 1% sediment, and 9% water. The water component varies as I note in a moment. More sophisticated analyses of hydrocarbon waste can give a more precise breakdown but I"m skipping that.
So sludge in an oil tank may be settled out solids from your oil as delivered, and/or it may include rust from the oil tank interior, particularly if there has been a fair bit of water in the tank or if (as sometimes happens) water was delivered mixed in with the fuel.
In More Reading above see the article titled OIL TANK WATER CONTAMINATION
Here is a nice quote from a 2010 US EPA article "Category Assessment Document for Reclaimed Petroleum Hydrocarbons: Residual Hydrocarbon Waste from Petroleum Refining" [copy on file or avail. from the US EPA.
Petroleum crude is a complex substance containing thousands of different organic hydrocarbon molecules. It contains 83-87% carbon, 11-15% hydrogen, and 1-6% sulfur.
Three types of hydrocarbons predominate: paraffins (saturated chains), naphthenes (saturated rings), and aromatics (unsaturated rings).
In many respects, the chemical composition of waste oils and sludges provides a snapshot of individual crude oil components at any particular stage of the refining process.
In some locations it may be possible to have received a delivery of contaminated home heating oil. For example, in 2013 the New York Times reported on an investigation of New York heating oil businesses who had "... cheated tens of thousands of customers for years, selling fuel diluted with recycled or waste oil ..." The report described raids on at least five heating oil companies located in and around New York City. Named in the article were Statewide and County Oil and several related or subordinate companies. 
Separately (not part of the raids, commercial and residential building owners filed class-action lawsuits against Castle Oil Corporation and Hess Corporation, making a similar claim - that waste oil had been mixed in with home heating fuel. The mixed, contaminated oil may have been delivered by independent trucking companies hired to deliver oil according to the article, and the report made clear that neither Castle nor Hess had come under scrutiny in the criminal inquiry. 
Watch out: on a much smaller scale, we also have occasionally encountered home or business owners who thought that it was a great idea to dispose of waste motor oil by dumping it into their heating oil tank.
Such mixing is not only illegal and stupid, risking loss of heat and related building damage, it also contaminates the environment by releasing toxic pollutants such as benzene, toluene, and xylene along with heavy metals such as mercury, lead, arsenic, cadmium, antimony lead, and zinc (all known carcinogens) in flue gases emitted by the heating appliances burning such an oil mix. Don't do this.
Reader Question: which way should the oil tank be sloped?
14 Aug 2015 Linc said:
When installing a new 275 gal oil tank, should it be tilted one way or another or should I keep it level? One person says to keep it tilted back away from the hole on the bottom so that any sludge goes to the back side of the tank. Someone elses says tip it the other way to make sure all oil can be used. Which is correct?
If the oil supply piping is taken off of the bottom of the oil tank, many installers tilt the tank away from that outlet - that is the low end of the tank is opposite the end to which the supply pipe is connected, in an effort to reduce the pick up of sludge by the oil piping.
If oil piping is taken off of the top of the oil storage tank then the pick-up end of oil piping will be stopped above the tank bottom to avoid picking up water or sludge, making the tank tilt not significant.
The suggestion that we want to "use all the oil" is a bad one. Most oil tanks will accumulate some sludge in the tank bottom over even just a few years of use. Sending that crud through the oil piping and into the oil filter or oil burner can lead to a costly loss of heat problem in the building. My opinion is that the financial cost of leaving a few gallons of oil (and often water and sludge) in the bottom of the oil tank is considerably less than the potential damage and repair costs of a loss of heat problem in a building during freezing weather.
Continue reading at EMERGENCY MEASURES for OIL TANK SLUDGE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
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Is this why i smell a oil smell when coming into the house. ? how do i know what caused this? - Anon 5/10/11
Sludge in the oil tank would not itself be the first cause of an oil smell in the home. More likely that odor would be from an oil leak in the piping system or an oil spill during fill-up. ALSO see ODORS FROM HEATING SYSTEMS the article link is found at page top or left
A more reliable and much less costly solution is to switch to natural gas. Imagine how much time and effort, not to mention anxiety late at night on cold nights when the heat stops, would be saved by eliminating the messy, apparently insoluble problem in the first place. - John Coburn 5/16/11
Both oil and natural gas as heating fuels have their own individual advantages and disadvantages. But the switch to natural gas is simply not an option in areas where no natural gas service is available. In those locations the switch would have to be from oil to LP gas, requiring the installation of a sufficiently large LP gas tank and appropriate piping, as well as of course complete replacement of the heating equipment.
Are there any standard extensions available to extend the furnace fuel line up into the oil tank? For a DIY, a 1/2" copper pipe fits snugly inside a 1/2" iron pipe nipple and the assembly screwed into the tank outlet. Is a 2" extension about right. Unless the tank is empty or nearly so this can be a little messy. - Gil 8/20/11
Of course if you are using a one-line oil system and relying on gravity, depending on where tank and oil burner are located, going to a two-pipe system could require more changes at the fuel unit, and more cost; It is probably possible to pump out the oil tank or use up most of its oil, try blocking the drain at tank bottom from inside temporarily, or just work quickly over a pan large enough to catch the brief oil spill as you remove the old fittings and install the new ones (having them ready and prepped at-hand).
Thanks for your comments. I did ask my oil company if they could pump out the sludge and they said no. I have had this company for a long time and they treat me well so I hesitate to go elsewhere. I used a 3 GPM oil pump to vacuum most of the sludge along the bottom of the tank but did not try to clean very far up the sides. I also pumped out the line to the furnace.
My furnace man did not recommend a line from the top unless we went to a two line system. That got a little pricey for a problem that seemed solvable another way. I did search suppliers of new tanks to see if they offered an extension piece with new installations but did not find any. I'll look further.
At this point there is about 8" of oil in the tank and I can lower a weighted plastic bag over the outlet to help minimize spillage when removing the outlet line. I have a temporary plug ready and then plan to replace the nipple in the outlet plumbing with my made up extension piece. The outlet plumbing includes a shut off valve which also helps minimize spillage. - Gil 8/12/11
Good project Gil. Send us some photos of your procedure and parts solution - it may help other readers. Use the CONTACT link at top, side, or bottom of any page
Mission is accomplished! The extension of the fuel line is in place in the oil tank and all is reassembled. The spillage was minimal, most was caught in a motor oil pan and plenty of newspaper for the splash. I did photograph the extension piece but it is simply a piece of 1/2" copper pipe inside a 1/2" iron pipe nipple. I did secure the copper piece with solder. I can e-mail more details if it would be useful but it may be a week or so. 8/13/2011
Our oil tank was installed ~ 15 years ago. It has a 2 pipe from the top system to deliver oil to the burner. The Company called it a continuous flow system. Yesterday a new tech came out to service the furnace and said we needed a filter on the line. Is this necessary for a 2 line top system? We lean to the if it isn't broke don't fix it school. - Kathleen 10/25/2012
Kathleen, no modern oil fired heating system should be run without a filter on the supply line ahead of the oil burner itself - doing so is asking for higher service costs and loss of heat as crud in the oil clogs the oil burner.
It's already "broke" and asking for trouble.
THE BLUE FLAME OF MY AGA/KEROSENE COOKER DISAPPEARED AND HEAT WAS REDUCED WHEN I LEFT THE DOOR THAT HOUSES THE BURNER OPEN FLAME RETURNED AND HEAT PLEASE EXPLAIN - Carol 11/20/12
Folks who shout in all caps get tiny font.
Watch out: your heating appliance may be unsafe - and may be lacking adequate combustion air; You need help from a qualified installer/repairman to be sure that your system has proper combustion air supply and that the air intake to the appliance itself has not become blocked.
I suggest having it examined by an expert. I suggest contacting AGA directly for help and to obtain a technical guide for your heater.
The size of combustion air inlet opening required for your AGA kerosene heater/cooker depends on the model and will be specified in its installation instructions; For example, the similar Rayburn 600K requires 61 cm2 of unobstructed air intake area. The company points out that for this model, an oil fired unit,
The air controls of the burner are factory pre-set, however small adjustments may be necessary to suit the site conditions. 
You will want to review the installation and operation manual for your AGA heater - easily downloaded from the company's website.
AGA, Station Road, Ketley, Telford, Shropshire, TF1 5AQ, UK, rayburn-web.co.uk
We're guessing that your Rayburn Heater is a UK device similar to the AGA heater. Rayburn makes cooking appliances, solid fuel, wood, oil, gas and electric heating appliances. Model specifications also vary between in-UK and export equipment.
For example the Rayburn Heatranger includes a cook stove, and it also provides hot water and/or central heating, thermostatically controlled to automatically maintain a constant temperature.
You can contact AGA, Redfyre, or Rayburn directly at AGA, Tel: 08457 626 147, or 08458 152 020, Website: rayburn-web.co.uk. In our references we include more contact information for AGA or Rayburn. 
The company's website provides links to both current and obsolete products' installation manuals and parts lists.
If you have not already done so, I would start by checking or replacing the oil filter that was supplied with your Rayburn heater. Usually the oil filter is located close to the wall where the oil line enters the building, or inside close to the heater itself.
Rayburn also requires a fire-safety heck valve in the oil line; check that your valve is not closed or jammed.
There are other things to check such as for an air leak or failure to purge air from the line after a de-clogging operation; I expect your service tech would also perform a vacuum test on the oil piping system.
My oil(#2) tank has the two line top feed. Trying to drain sludge and or water from the tank I opened the valve at the bottom of the tank and nothing flows out. There is a little oil/water (I'm guessing) in the outlet. I tried poking the plastic sleeve of a 12ga. wire through in case the valve is clogged with sludge.
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When I open and close the valve all I see is a small pin of brass(?) going up and down in a much larger area.
I do not see a gate moving in the valve. I haven't been able to find helpful information about the valve(body reads Lunkenheimer) on the internet. What if anything can you tell me about this valve or why it doesn't seem to be doing anything. Thank you.
It sounds as if the tank bottom drain is plugged with sludge - if in fact it's a valve. A small brass pin ? Sounds like an air valve (looks like a tire valve) that would have no business being installed on an oil tank. More likely I just didn't understand your question.
[Photos above & below illustrate this oil tank valve made by Lunkenheimer]
At below left we see the Lunkenheimer oil tank valve in the "closed" position. At below right the reader's photo shows this valve when the valve handle & stem are in the "partly open position" - you can see virtually no change in the actual valve opening.
Watch out: I would not mess with a tank bottom valve at all in this situation; if you start disassembling or unscrewing and your oil tank suddenly spits out its sludge plug, you could have a flood of heating oil on the floor, creating a costly catastrophe.
That's perhaps why oil companies prefer to try pumping sludge and water out of the tank from the tank top, along with adding an oil tank additive that is intended to break up sludge (and can quickly clog the heating oil burner or its filter).
Indeed Lunkenheimer is a producer of a range of control valves used on heating equipment.
You can perhaps identify and then read about your particular valve in the Lunkenheimer product catalog available at the company's website. lunkenheimercvc dot com [no links are included in comments for security reasons] or you can contact the company's U.S. outlet at Cincinnati Valve Company
sales AT lunkenheimercvc [dot] com
P: 513.471.8258 | F: 513.471.8327
P. O. Box 141451, Cincinnati, OH 45250-1451, U.S.A.
Before I contacted you I did go to Lunkenheimer's site. Not being a mechanic or engineer I did not see anything there that helped me. Yes, without pictures or a better description it would sound like an air valve and for all I know and what I know about the previous owner of this house it could be. Here are the pictures.
Great photos. Bad news. It looks as if the gate valve is not opening; We could be looking at a backflow preventer mechanism, but I suspect that instead, on this valve the gate stem is broken inside the valve - so it doesn't lift the gate. If the valve seems to turn a bit easily and in particular if in turning the handle the handle stem doesn't move up or down it's probably not moving the actual gate in the valve. On some gate valves the stem will actually turn and even rise up or move down in the valve body, but as the stem end has broken away from the valve gate, the valve never actually opens or closes. This is what I think is happening with your valve.
The oil tank valve photograph below shows this same Lunkenheimer valve in the fully "open" position - actually it's not open.
Instead of trying to replace this valve, I'd prefer to see the valve opening capped so that it cannot leak at all. Then address the oil tank sludge in the other ways we've discussed.
A plumber, putting down a big pan to catch spilling goop, and who was very nervy and very confident might be willing to try to replace the valve but considering the costs of trying to clean up a big oil spill I figure most will not be willing to touch it. Or an plumber experienced with changing out valves on live water lines might try freezing the short pipe nipple connecting the valve to the tank, then swapping out the valve. But again, it's a risky proposition that, considering how sludge clogs stuff up, probably is not the best approach anyway. I speculate that even if you opened the valve the sludge would clog that opening before accomplishing any useful sludge removal.
BE CAREFUL as I warned before, I'm worried that you'll open the valve and not be able to shut it - flooding the place with oil.
Usually the oil co will pump out as much sludge and water as they can - from a fitting at the tank TOP, then use the additives I cited - like 4 in 1 HOT pour point depressant that also includes a sludge dissolver.
I speculate that the sludge is so goopy that it's not going to flow out of the valve even if you could open it (water would).
If we're working on this because your tank is picking up sludge through the tank top fitted oil line(s) the fix is more often to raise up the lowest end of the tank oil pickup line that inserts into the tank from the top - get it above the sludge level. That may mean you will draw a bit less oil out of the tank before needing a new delivery, but usually that will get you by until you're ready to replace the tank (or if it's tested and found sound you could have the tank professionally cleaned - but we don't ususally find that cost justified for residential oil tanks);
In addition to drawing up the lower end of the oil pickup line from the tank top, on a similar problem system we installed double oil filters, side by side, in parallel, so that we could filter out the stirred-up sludge (from oil deliveries) without having the oil filters clog early. (Oil filters get replaced at annual service). I speculate that valve stopped working a long time ago, after having served for years as a connector to a bottom-connected oil line. The then owners or their service tech realized the danger of trying to change it and instead left it in place, closed, opting to change over to taking oil from the top of the oil tank.
(July 31, 2014) Linda said:
OK. I have an original?(1940) above ground 275 fuel oil tank that presently is @ 1/4 full.
I want to add Hercules Fuel Oil sludge treatment to it & wonder the following: if 1 pint is recommended dosage for this size tank, and I only want to order 100 gals of oil (as we may change systems before winter) how much should I pour in before the delivery & how soon after pouring should delivery be done?
I asked my fuel oil supplier and he said he didn't know. I called Hercules, who sold to Ody? and a diagnostic expert said it's best to add it in when tank is empty--as the container treatment also states "as low as oil level as practical". Since the chemistry that needs to take place is emulsification, can I get away with just ordering 100 gals and using half a pint? Or is there some other methodology? Thank you very much.
Take a look at the treatment advice on the product label. Typically the dose is a bottle for 250g of heating oil. I can't imagine any benefit to adding the treatment with the tank nearly empty though I can imagine what your diagnostic expert may have himself or herself imagined even if it's not the manufacturer's recommendations. We'll skip that.
Yes of course you could adjust the dose to match the delivery quantity of oil or tank quantity of oil.
The product both breaks up sludge and helps remove oil, in theory transporting them through the piping and burner to be consumed.
The best time to add a treatment is immediately before an oil delivery - as then the delivery mixes the treatment with the new oil and also (usually) stirs up sludge and water in the tank.
WATCH OUT: you may find you need to change the oil filter at each oil burner frequently (or install higher capacity filters) lest the filter clog with the sludge that's now moving through the system. You'll read in the article above that we had to do that to keep the oil burner running between annual cleanout service times.
I add that if there is a lot of water in the tank it should be pumped out.
(July 31, 2014) Linda said:
Thank you; you've helped. Instead of changing the filter, we cleaned (washed) it & it came out
as new; but I will be on lookout for any slowdown coming aaro the emulsified sludge now coming thru the system.
Nice to put knowledge to work!
Good for you. Oil filter cartridges are really cheap - I suggest buying a half dozen and putting them to work.
20 January 2015 Ameenah said:
I was wondering if high pressure could cause problems with my oil heater ?
My neighbor got a new water pipe run underground, that was Friday, after it was done, I noticed my pipes started clanking and the water in my kitchen would come on very and it had force behind it, when I first tuned it on in the morning. Tuesday, my heater shut off, it is a connection to the plumbers being underground or it is a coincidence, the clanking and the water pressure in the kitchen did not take place until after the plumbers went underground.
Could there be a connection to the heater and the water pressure ?
I'm unclear why your neighbor's piumbing work changed your building water pressure.
But yes an increase in building water pressure can cause water hammer problems as valves at sinks or even heating zones turn off.
for details on diagnosing and fixing these noises.
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