Guides · Buying
Buying a house with an oil tank in Seattle
A buried heating oil tank is not automatically a dealbreaker. An undocumented one often is: not because of the tank itself, but because your lender may decline to fund the loan, and because a leak is a cleanup bill nobody has agreed to pay yet.
What an old oil tank looks like#
Why this stops deals#
Thousands of homes across Seattle and the north-end suburbs were heated with oil before converting to gas or electric. In many of them the tank was never dug out. It is still in the yard, or under the driveway, usually forgotten.
The problem is rarely the steel itself. It is that three separate parties each get a say, and any one of them can end the transaction. Buyers and lenders may ask for proof the tank was decommissioned. Insurers often exclude the resulting contamination from a standard homeowner's policy. And the City of Seattle notes cleanup costs for an oil leak can exceed $10,000, which is a number that has to land on somebody.
None of that is visible on the listing. It surfaces during inspection, at which point you have days rather than weeks to work out who is paying.
Sources
- The hidden risks beneath your yard: retiring your oil heating tank, City of Seattle
- Heating oil tank programs and pollution liability, Washington Pollution Liability Insurance Agency
- Decommissioning of Residential Heating Oil Tanks (CAM 5962), Seattle Fire Department: permit code, procedure and certification requirements
Have an address in mind already?
Book a call and I'll tell you what I'd doThree states a tank can be in, and only one is fine#
Almost every argument about oil tanks comes from people using one word for three different situations.
Still in service means the house is heated with oil and the tank is live. That is a known quantity. It works, it has a fill pipe, and it can be converted later. It is not a hidden problem.
Decommissioned means the tank was taken out of service under a Seattle Fire permit, either dug out, or emptied, rinsed and filled in place, with a record showing the work was done to standard. This is the common and generally accepted outcome. The paperwork is the whole point.
Undocumented means somebody stopped using it and walked away. No permit, no certificate, no record, no soil testing. This is the one that costs money, and it is far more common than sellers realize, because a previous owner did it and nobody has thought about it since.
One rule worth knowing before you ask anything: under Seattle Fire Code, a tank out of service for twelve months or more must be decommissioned, by removal or by filling in place. A tank that has simply sat unused since a gas conversion in the nineties is not in a neutral state. It is out of compliance, and that is the seller's problem until you agree to make it yours.
What the records and costs say#
The permit. Seattle requires a Fire Department permit (Permit Code 6103) before a buried heating oil tank is removed or filled in place. It costs $184 per tank, and it is issued to the contractor, not the owner. The permit does not require soil samples, but Seattle Fire says a tank suspected of leaking should be removed, not filled.
The records. Seattle Fire's public list shows 50,253 residential tank permits since 1996. About 70% were filled in place and about 24% were removed. The City estimates 8,000 to 10,000 Seattle homes still heat with oil.
The cost. In 2020 the City said decommissioning starts at about $1,800 plus tax and permit, and that cleaning up a spill can exceed $100,000. Get a current quote on the actual tank.
The 2028 date. You may read that Seattle requires every tank gone by 2028. A 2019 City ordinance asked City departments for a plan toward that date. In 2020 they recommended outreach and monitoring rather than a new rule. Seattle Fire's current guidance cites only the one-year out-of-service rule.
Sources
- Seattle Fire: residential heating oil tank permits (data.seattle.gov), search by address; updated daily
- Seattle Fire permit form 6103, $184 per tank
- City of Seattle heating oil memo, June 30, 2020, cost figures and the 2028 goal
- Seattle Clean Heat program, oil-to-electric rebates
- PLIA Heating Oil Loan and Grant program, up to $75,000
- WAC 173-340-300, the 90-day reporting rule
How to check before you write the offer#
Most of this is public and free, and it takes under an hour. Do it before the offer rather than during inspection, because your leverage is much better before you are in contract.
- Look for the physical signsA fill pipe or vent pipe near the foundation, a capped pipe in the driveway, or a patch of settled ground in the yard. Oil-era houses often still have the pipes even when the tank is long dead.
- Search the decommissioning recordsSearch Seattle Fire's public list of residential tank permits on data.seattle.gov by address. It goes back to 1996. Get the certificate rather than a verbal assurance. A record with missing tank details means the final report never reached the Fire Department. A tank with paperwork and a tank without are different properties at the same price.
- Know which permit you are asking aboutSeattle requires a permit before an underground tank is decommissioned: Permit Code 6103, Residential Heating Oil Tank Decommissioning, issued by the Seattle Fire Department. Ask the seller, in writing, for that permit number and the Fire Department's decommissioning report form. If the work was done properly, both should be easy to find. A vague answer is a warning sign.
- Check who did the workDecommissioning must be carried out or supervised by an ICC-certified underground storage tank decommissioner. "A guy filled it with sand" is not the same thing, and a lender or insurer will treat it as untouched.
- Read the seller disclosure carefullyWashington's Form 17 asks the seller about known conditions. Read what they said about heating systems and storage tanks, and note what they did not say. Silence is information.
- Ask for a tank scan, not just a home inspectionA standard home inspection does not locate buried tanks. Locating one is a separate service, and it is inexpensive relative to what it protects you from.
- If a tank is found, get soil testing before you agree to anythingThe tank is not the cost. Contaminated soil is the cost, and the only way to know is to test. Agreeing to a repair credit before testing means agreeing to a number nobody has calculated.
- Call your lender before you negotiateAsk directly whether they will fund the purchase as-is, with a decommissioning certificate, or only after removal. Their answer determines what you can even ask for.
- Ask about state assistance programsThe Washington Pollution Liability Insurance Agency's free heating oil insurance ended June 30, 2025. Its Heating Oil Loan and Grant program offers up to $75,000, including cleanup grants of up to $60,000 per tank. Only the property owner can apply, so before closing that is the seller. The next window is November 2 to December 17, 2026.
- If anyone suspects a leak, report it quicklySeattle's oil tank flyer says to report a suspected leak within 24 hours to 1-800-OILS-911 and stop automatic oil deliveries. State rules require the owner to report a suspected or confirmed leak to the Pollution Liability Insurance Agency within 90 days. Before closing, the owner is the seller, so ask whether it has been reported.
Rules, programs and costs change, and they differ between Seattle and each surrounding city. Figures on this page are dated where they appear. Confirm anything specific with the relevant city or agency before you rely on it.
What to do with the answer#
If the tank is decommissioned with a certificate, this is usually a non-event. Confirm your lender agrees and move on.
If a tank is present and undocumented, it is a negotiation, not a walk-away. The seller can decommission before closing, fund it through escrow, or reduce the price. Which one is right depends on your timeline and on what your lender will accept.
If soil testing shows contamination, slow down. That is a different conversation with different professionals in it, and it is not one to resolve inside a five-day inspection window.
Common questions#
Can I get a mortgage on a house with a buried oil tank?
Often yes, but it depends on the lender and on the documentation. A decommissioned tank with a certificate is usually acceptable. An undocumented tank can be a problem. Ask your lender the specific question before you negotiate, because their answer determines your options.
Does the tank have to be removed, or is decommissioning enough?
Filling in place is the most common method in Seattle, about 70% of permits since 1996. Seattle Fire says a tank suspected of leaking should be removed instead, and a tank filled now may need removal later at extra cost. What matters most is that whichever was done was permitted and documented.
How much does it cost to decommission an oil tank in Seattle?
The Fire Department permit is $184 per tank. In 2020 the City said decommissioning starts at about $1,800 plus tax and permit. Cleaning up a spill can exceed $100,000. Get a current quote on the actual tank.
Who pays to deal with it, buyer or seller?
Whoever has less leverage. That is genuinely the answer. It is a negotiated item, and it moves with how long the home has been listed, whether there are competing offers, and whether the seller knew about the tank before you told them.
Will my homeowner's insurance cover a leak?
Frequently not. Contamination from an underground storage tank is commonly excluded from standard policies, which is why the cleanup cost tends to fall on the owner. Confirm with your own insurer rather than assuming. The state's free heating oil tank insurance (PLIA) ended June 30, 2025.
How do I find out if a tank was decommissioned?
Search Seattle Fire's public list of residential tank permits on data.seattle.gov by address, and ask the seller for the decommissioning certificate. A seller saying it was taken care of, without paperwork, is the situation this page exists for.
Who should I actually talk to first?
In order: your insurance agent, then your lender, then a decommissioning contractor. And your broker throughout, because the outcome is a negotiation rather than a repair. Most advice on this question is written by tank removal companies and points you straight at a contractor quote. That is the third call, not the first. The quote only matters once you know whether the house can be insured and financed at all, and who is going to pay.
Related guides
- What buying in Seattle actually costs: the Seattle buyer's guide
- Buying a Seattle house with foundation issues
- What to look for when touring a house in Seattle: a printable checklist
- How to buy a house without a realtor in Seattle
