You went downstairs to grab something from the freezer, glanced over at the corner where the furnace lives, and there it is. A dark, wet patch on the concrete under your oil tank. If your first thought was “how much is this going to cost me,” you’re in good company. A wet spot under an oil tank is one of the most common reasons homeowners across Greater Moncton pick up the phone and call us, and here’s the honest answer up front: it’s not always a leak.
Sometimes it’s condensation. Sometimes it’s a drip from a loose fitting that costs a couple hundred dollars to sort out. And yes, sometimes it’s the first visible sign of a tank that’s been rusting from the inside for years. The trick is figuring out which one you’re looking at, because the gap between catching a leak early and catching it late can be tens of thousands of dollars.
Let’s walk through it the same way we would if we were standing in your basement with you.
Don’t Panic Yet: A Wet Spot Has More Than One Explanation
Heating oil tanks sweat, drip, and stain for all kinds of reasons that have nothing to do with a hole in the steel. Before you start pricing out a whole new furnace room, take a breath and look closer.
The three broad possibilities are water, a minor oil drip, and a genuine tank leak. Water usually means condensation, a damp foundation wall, or a plumbing issue nearby. A minor drip usually comes from a serviceable part like the filter, a valve, or a fitting. A genuine leak usually starts at the bottom of the tank, where sludge and water have been sitting against the steel year after year.
Only one of those three is an emergency. The other two are maintenance. So your first job isn’t to panic, it’s to identify what’s actually on your floor.
One safety note before we go further. If oil is visibly running or pooling, or you can smell it strongly through the house, skip the detective work. Slide an old bin or tray under the drip if you can do it without touching the tank, and call our 24/7 emergency line at (506) 806-0900. A leaking tank is not a wait-until-Monday problem, and our emergency oil tank service exists for exactly this situation.
How to Tell If the Wet Spot Under Your Oil Tank Is Oil or Water
Here’s the test we teach every homeowner, and all it takes is a paper towel.
Press a clean white paper towel into the wet spot and look at what comes up. Water soaks in clear and dries without a trace. Heating oil leaves a yellowish or brownish stain with a distinct petroleum smell, a bit like diesel, and it won’t evaporate. If you’re still not sure, leave the towel on a shelf for an hour. Water disappears. Oil doesn’t.
Use your nose too. Furnace oil has a strong, unmistakable odour. If the basement smells like a garage, that’s a meaningful clue before you touch anything. We wrote a full guide on what an oil smell in your basement means if the smell is your main symptom.
Then put your eyes on the tank itself, not just the floor:
- Run a gloved hand along the bottom of the tank. A failing tank often “weeps” before it drips, leaving a sticky, oily film along the bottom seam.
- Look for rust blisters, flaking paint, or a wet-looking line on the underside. Blistered paint on the belly of a steel tank is a classic late-stage warning.
- Check the fittings: the shut-off valve, the oil filter housing, the gauge, and the spot where the oil line leaves the tank. A drip that traces back to one of these parts is usually a cheap fix.
- Look at the legs and the floor around them. A tank that has shifted or sunk puts stress on the fittings and can start a drip that looks like a tank leak but isn’t.
If the towel comes up clear and odourless, you’re likely dealing with condensation or basement moisture. If it comes up oily, keep reading, because the next question is where the oil is coming from.
Common Causes of a Wet Spot Under an Oil Tank
Condensation, the mostly harmless one
Steel tanks sweat. In spring and summer, warm humid air hits the cold steel of a partly empty tank and moisture beads up on the outside, then drips onto the floor. Outdoor tanks do the same thing in the coastal humidity around Shediac. Condensation on the outside won’t hurt your floor, but it points to a bigger issue: those same temperature swings pull moisture inside the tank, where it sinks below the oil and quietly rusts the bottom from within. That’s one reason we tell people to keep the tank topped up through summer.
A drip at the filter, valve, or fittings
The oil filter beside or below your tank has a gasket that hardens with age. Valves loosen. Compression fittings on the oil line can seep. These drips are slow, they stain the floor directly below the part, and a technician can usually fix them in one visit for $150 to $350. Annoying, but cheap.
An overfill or delivery spill
Sometimes the wet spot shows up right after a fill. A burp from the vent or a drip at the fill pipe can leave oil on top of the tank that runs down and pools underneath. It looks alarming and usually isn’t, but it’s worth confirming rather than assuming.
Internal corrosion, the one that ends tanks
Here’s the part that surprises people: steel oil tanks almost always fail from the inside out. Water and sludge collect in the bottom, and corrosion eats upward through the steel. The U.S. EPA’s storage tank program documents this same failure pattern in its guidance on tank corrosion and releases. By the time you see a weep, a blister, or a wet spot on the outside, the steel at that point can be paper thin. That’s why a “tiny” weep on a 25-year-old tank is treated as a replacement, not a repair. Rust blisters and flaking paint on the tank belly are the outside evidence of that inside damage, and they deserve the same respect as a visible drip.
What a Wet Spot Can Cost: Three Greater Moncton Outcomes
The same symptom can end three very different ways. These are the kinds of calls we take every month.
Riverview, caught early. Denise in Riverview found a damp ring under her 1998 steel tank in March and did the paper towel test that night. Oily. She called the next morning, we confirmed a weeping bottom seam, and we swapped the tank for a new double-bottom Granby before it dripped a single full drop. Total cost: $3,450 installed, old tank hauled away. No cleanup, no insurance claim, no drama.
Shediac, false alarm. Marc near Pointe-du-Chene was sure his outdoor tank was finished when he found water pooled under it in June. The towel came up clear. It was condensation plus a clogged downspout soaking the pad. His cost for the diagnosis was $0, since our written estimates are free, and about $220 to replace a corroded filter assembly we spotted while we were there.
Memramcook, caught late. The hard one. A family in Memramcook noticed a faint smell and a stain in the fall, figured it could wait until after the holidays, and by January the tank had let go into the soil beside the foundation. Environmental cleanup, soil testing, and remediation ran past $28,000, and the insurance back-and-forth added months of stress. The new tank was the cheapest line on the whole invoice at $3,200.
Same starting point, three different endings. Here’s the honest range of where a wet spot can lead:
| What you find | Most likely cause | Typical cost in Greater Moncton (CAD) |
|---|---|---|
| Clear, odourless moisture | Condensation or basement damp | $0 to $150 |
| Oily drip traced to filter or fitting | Worn gasket, loose valve or fitting | $150 to $350 |
| Oily weep or blister on tank bottom | Internal corrosion, tank failing | $2,800 to $4,500 for replacement |
| Spreading oil stain, strong odour | Active leak reaching floor or soil | $15,000 to $40,000+ for cleanup |
That bottom row is the whole argument for acting fast. Nobody has ever regretted replacing a tank one year early. Plenty of people in southeast New Brunswick have regretted replacing one six months late.
What to Do Right Now, Step by Step
If the towel test says oil, here’s your order of operations.
- Contain the drip. Slide a metal or plastic tray, an old baking pan, or a bin under the wet spot. Absorbent pads or even kitty litter around the area will keep oil from spreading across the concrete.
- Don’t move or tip the tank. A corroded tank can fail completely if it gets bumped or shifted. Moving several hundred litres of oil is a job for people with pumps and insurance, not for you and a brother-in-law on a Saturday.
- Keep sparks away. No grinders, no space heaters, nothing with an open element near the spill. Furnace oil isn’t explosive like gasoline, but you still don’t want ignition sources beside it.
- Take photos. Time-stamped pictures of the wet spot, the tank bottom, and the tank’s nameplate help with the service call and any insurance conversation later.
- Call a professional. This is where DIY ends. A licensed technician can check the fittings, inspect the shell, and tell you in one visit whether you’re looking at a $200 fix or a tank replacement.
- If oil has reached soil, a drain, or water, report it. In New Brunswick, spills must be reported to the 24-hour environmental emergencies line at 1-800-565-1633, coordinated through the Department of Environment and Local Government. Reporting promptly protects you legally and usually keeps the cleanup smaller.
If oil is actively leaking, our step-by-step leaking tank guide covers the first hour in more detail. And whether it’s a drip or a gusher, you can reach us around the clock at (506) 806-0900.
Repair or Replace? How to Make the Call
Once a technician confirms where the oil is coming from, the decision usually makes itself.
Repair makes sense when the leak traces to a serviceable part: the filter, a valve, a fitting, the gauge, or a stretch of oil line. The tank shell is sound, the part gets replaced, and you’re done for a few hundred dollars.
Replacement is the only smart call when oil is coming through the tank shell itself. There’s no safe, code-compliant patch for a weeping steel tank, because the corrosion you can see is never the only corrosion there is. Age matters too. If your tank is past 15 years old, or you can’t prove its age at all, many insurers in New Brunswick will force the issue anyway. If you’ve already had one of those letters in the mail, you know exactly the pressure we mean.
A straightforward oil tank replacement in Moncton typically runs $2,800 to $4,500 installed, including removal and disposal of the old tank, and most swaps are finished in a single day. Modern double-bottom and fibreglass tanks carry warranties of 10 to 25 years, which your insurer will like as much as you do.
If you’re staring at a wet spot right now and want a straight answer instead of a guess, request a free written estimate. We’ll tell you plainly whether it’s condensation, a cheap fix, or time for a new tank, and we’ll put it in writing either way.
Frequently Asked Questions
Is a wet spot under my oil tank always a leak?
No. Condensation, basement dampness, and drips from serviceable parts like the filter or valves cause plenty of wet spots that have nothing to do with a failing tank. The paper towel test is the fastest way to tell: water dries clear, while oil leaves a smelly yellowish stain that won’t evaporate. If the towel comes up oily, treat it seriously and get the tank inspected promptly.
How long can I wait if the wet spot turns out to be oil?
Don’t wait. A weep can hold steady for months or let go in a week, and there’s no way to tell from the outside because the corrosion is happening inside the steel. Waiting turns a $2,800 to $4,500 planned replacement into a potential five-figure cleanup. Contain the drip, take photos, and get a professional to look at it within days, not weeks.
Will my insurance cover a leaking oil tank in New Brunswick?
It depends on your policy and, heavily, on the age and condition of the tank. Many policies exclude leaks from tanks past a certain age, and a known drip you ignored can void coverage entirely. Cleanup from oil that escapes into soil is exactly the scenario insurers scrutinize hardest. Our guide on whether insurance covers oil tank leaks walks through the fine print.
Who do I call if oil is actively leaking right now?
Call Hub City Tank Co’s 24/7 emergency line at (506) 806-0900 right away, and put a tray and absorbent material under the drip if you can do so safely. If oil has reached soil, a floor drain, or water, also call New Brunswick’s environmental emergencies line at 1-800-565-1633. We serve Moncton, Dieppe, Riverview, and communities across Westmorland, Albert, and Kent counties.