There are certain places in your home where you wouldn't be surprised to see a leak: under the sink, on the floor around the water heater, behind the washing machine. But water around furnaces is more unexpected and the cause more perplexing.
You can easily troubleshoot the cause, though you might want to leave the actual fix to an HVAC technician. It's worth the cost of a service call to ensure the system is properly fixed.
Clogged Condensate Pump
If you have central air conditioner, your furnace is likely part of that system. The furnace will contain the evaporator coils that become cold when refrigerant cycles through the system. An adjoining blower fan sucks the hot air out of your home and across those coils. The air then pushes back out your vents to cool your home.
The process that makes the evaporator coils cold also produces some moisture. That moisture has to drain out of the furnace somehow, or you'd have a flooded furnace. If your furnace is in the basement or some other area where gravity can't help with drainage, your system likely has a condensate pump.
A condensate pump removes water from the furnace and pumps it down a drain pipe. Dirt buildups or frozen water can create a clog in the pump. The clog makes excess water backup into the furnace and that excess water can then spill out onto the floor.
If you have some do-it-yourself experience, you can consult your owner's manual for instructions on how to replace your model's condensate pump. Otherwise, call an HVAC tech, like those at Summers & Smith Cooling, for help.
Frozen Evaporator Coils
If you've recently had a heat wave followed by a cool down and found water, there's a chance your evaporator coils are freezing when the air conditioner is running. The coils can freeze due to low refrigerant or a faulty blower fan. Then, when the system is off for a day or two, the ice has a chance to melt and drip down as water.
Your condensate pump or drain is meant to catch that water and direct it out of the furnace. But that's not a foolproof system, so some of the melted ice can still end up on the outside of the furnace.
A HVAC tech has to take care of the refrigerant levels, due to the sensitive nature of the chemicals. It's also worth having the tech come out even if you suspect a blower fan issue, since this is tough to repair on your own.