Isn’t it just the last thing you need during the crazy rush right before the holidays? Your maintenance guy tells you there’s a puddle of water under your furnace. Oh, great… there goes your dream of a profitable December and starting off the New Year with a trip to the tropics. Will you have to shell out thousands for a new furnace instead?

Don’t cancel your plans just yet! There are a number of reasons that can lead to your furnace leaking water, and most of them don’t mean an untimely death for your heating system.

Start by identifying what type of heating equipment you have, and check out these possible causes for water leaks.

1. High-efficiency furnace

If you have a newer high efficiency furnace (with an Annual Fuel Utilization Efficiency or AFUE rating of 90 percent or more), these systems extract heat from the exhaust which produces condensation. Normally, the condensation is drained through a tube to a pan or floor drain. If there is a clog or a break in the drain line, or if the floor drain is clogged with debris, you could end up with a puddle under your furnace.

Check the drain first and clear it if necessary. If the drain line appears compromised, this is an easy fix for an HVAC service technician.

2. Furnace with a humidifier

Do you have a furnace with a humidifier attached? If so, the humidifier could have a leak, or it could be clogged and overflowing into your furnace. If you catch this early, it may not be a major expense to clean out or even replace the humidifier. But if the leak goes on for a while, it can cause major damage to your furnace. Call an HVAC expert as soon as possible to inspect your system.

3. Combined heat and air conditioning heat pump system

If you have a combined heating and air conditioning system with a heat pump, the water leak could actually be coming from the air conditioning. These systems have a combined drain line which could be clogged. If you are still using the air conditioning occasionally, the coils could be frozen or the condensate pump may have failed. Even if you suspect the water is coming from the air conditioner, don’t neglect this issue because water leaks can ultimately cause damage to your building’s walls, ceilings and floors.

This may turn out to be a minor repair, but you need to call an HVAC service company with expertise in combined heating and air conditioning systems.

4. Newly-installed gas furnace

If you’ve just bought a new gas furnace and it’s already leaking, you’re probably pretty steamed. Chances are, you went with the lowest bid and got installers who are not the most experienced (or just trying to cut corners so they make money on the job).

There are several installation mistakes that can cause water leaks from a gas furnace. The flue pipe that exhausts the toxic gases from your building could be the wrong size, or there could be a leak in the joint between the furnace and the outside vent pipe. Also, the exhaust pipe may have been incorrectly installed; it needs to slope slightly downward toward the exterior so that water drains out of the building rather than back into the furnace.

5. Hot water boiler

If your heating system is a hot water boiler with baseboards or radiators, anytime you have a leak you should immediately close off the valve that feeds water to the system. If your slow drip is the precursor to a major leak, you’ll save yourself from a big mess by limiting the amount of water in the system until you can get an HVAC repair guy in there.

The problem is likely to be just a faulty valve. Especially if you’ve recently had a repair done, it’s possible that air was introduced into the system which increases the pressure on the valves. You’ll have to get the repair technician to come take another look. In the worst case, you may have a leak in your boiler, and there’s a chance it will need to be replaced. Call “Green Apple Mechanical NJ” toll free at

  • (888) 611-7191

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