Does a Furnace Use Water?

You might have heard that furnaces can leak water. But does that mean that these units use water?

Regular furnaces do not require water to work; however, condensing units can create water during their operation. Steam and hot-water heating systems, hydronic forced-air heating systems (combined hydronic air handlers), and indirect water heaters are the units that do use water.

Does a Furnace Need Water to Work?

So, does a furnace use water? A gas or an electric furnace does not require water to work.

All the units definitely need air as that is the thing that they will be heating up. Depending on the system, your furnace is going to also need electricity or gas and electricity.

Once the unit gets the signal from the thermostat (or you simply turn the furnace on), it will start taking in the air (either from outside or from your house). The air will then get heated up and sent throughout your house.

No water will be involved in the process.

Read: Is Furnace Condensate Toxic?

What Kind of Furnace Uses Water?

If you prefer to heat your house with a boiler, then your unit is going to need water in order to function.

Here is how steam or hot-water heating systems work:

  1. The thermostat tells the boiler to turn on.
  2. Once the boiler starts working it uses electricity, gas, or oil to create heat.
  3. The heat is used to warm up the water that is concentrated inside the boiler.
  4. Later on, the hot water (or even steam) gets sent throughout your house via pipes and radiators or radiant floor systems.
  5. In a while, the steam will condense or the water will cool down. The liquid gets sent back to the boiler and the cycle repeats until the house reaches the desired temperature.

So, boilers really do need water to heat your house.

The majority of the units lose some H2O during operation. The actual system should be able to monitor the level of water on its own and add the necessary liquid if there ever is such a need.

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In case the boiler continues running without enough water, the device might get damaged or might even start a fire.

Read: Why Furnace Blower Motor Is Making Noise When Starting?

Does a Hot Air Furnace Use Water?

Not only steam and hot-water heating systems use water. There are also hydronic forced-air heating systems that use water as a medium of heat transfer.

Such a system can be called a ‘combined hydronic air handler’ or a ‘hot water furnace’.

It consists of a high-efficiency water heater and a hydronic air handler. Once there is a call for heat, the pump will start sending hot water from the water heater to the coils located inside the air handler.

The cool air gets pushed over the coils and the hot water inside the coils warms up the air. The heated air then gets sent into the ducts.

In such a system, the water heater is also able to produce hot water for the whole house.

Fact: a combined hydronic air handler can work as an air conditioner as well.

Read: Is It Worth Getting A High Efficiency Furnace? And Why?

Does a Furnace Have Water in It?

Even though regular furnaces do not need water to operate, some of them can create water.

A standard-efficiency or conventional furnace does not produce any liquid. However, if you are an owner of a high-efficiency furnace (a unit that has an efficiency rating of over 90%), then you might have noticed that the unit produces water.

To find out, if you have a high-efficiency furnace or not, find the exhaust pipe. Condensing units are going to have a white plastic PVC pipe, while conventional furnaces have a metal exhaust pipe.

A high-efficiency or condensing furnace produces water because it has a second heat exchanger.

The exhaust gases don’t leave the system as soon as they pass through the first heat exchanger, they travel to the second heat exchanger where even more heat gets extracted (that’s why these units are high-efficiency – no heat gets wasted).

The exhaust gases cool down to a point that the water vapor in them turns into a liquid. This condensate then gets drained. 

Does a Furnace Heat Water?

Boilers and combined hydronic air handlers that we have mentioned before heat water and use it to keep your house warm.

Regular furnaces do not heat water.

However, there are water heaters that can work in combination with a furnace. Indirect water heaters don’t have their own heating element – they use the heat from the furnace to warm up the water.

In such a system, the two units are connected via a pipe through which the water circulates.

Read: How To Clean Gas Furnace?

How Do You Add Water to a Furnace?

  • A boiler

Turn off the heat and wait for the boiler to cool down. Check the water levels to figure out how much water you should add.

Simply pull the water feed valve’s handle to add water. Keep monitoring the water levels, to find out when to push the handle back up.

  • A combined hydronic air handler

In the majority of cases, the air handler in this system is combined with a water heater. 

Before adding water to your water heater make sure that the drain valve is closed. Find the cold-water supply line and open the shut-off valve.

Open every hot water faucet. As soon as you see a steady flow of water coming from the faucets – your water heater is full.

  • An indirect water heater

Just like a standard water heater, an indirect unit has a cold-water inlet through which it gets filled with potable water.

Can Water Damage a Furnace?

Unfortunately, practically no HVAC equipment would be able to survive serious water damage.

The units have sensitive electronics inside and these will be the first things to stop working. Moreover, rust can eventually form on the units that have been submerged in water.

Will Water Ruin My Furnace?

The chances are high that you would have to fully replace your furnace. The best thing that you can do is call an HVAC expert who is going to check all parts of the system.

Warning! Turning the furnace back on even after it had fully dried might be dangerous.

While you’re waiting for the specialist, you can have a quick look at your unit.

  • You can figure out how high did the water get. Look at the outdoor components and try to find dirt in the fins.If the water got 2-3 inches above the base, then there is a chance that no serious damage had been done. However, if the water rose higher than that, then you might have to replace the unit.
  • Address the indoor components. If the furnace is located in the basement, then it might have not survived.The good news is that the units that are installed in a utility room on the 2nd floor, for example, might be ok.

Why Is There Water at the Bottom of My Furnace?

If you have a conventional furnace, then…

  • The exhaust pipe might be creating condensation.

If you have a high-efficiency furnace, then…

  • The condensate pump isn’t working
  • There is a clog or a leak in the condensate line

Issues that can cause a water leak in any furnace:

  • A leaking humidifier
  • A cracked heat exchanger
  • A dirty furnace filter

Read: How Often To Change Furnace Filter?