9 Tips on How to Drain Furnace Water Properly

As furnaces run, they build up condensation. This is normal, however that very water buildup can also cause serious damage to the furnace if it isn’t drained properly. As such, it’s important to ensure your furnace’s drain is in good working condition.

Here are the nine tips on how to drain furnace water:

1. 90% gas furnace

Different types of furnaces may require slightly different methods for draining. The following method speaks specifically to a 90% gas furnace (also known as high efficiency or condensing furnaces). The reason the high efficiency furnace is the most important furnace to focus on is because these units typically generate a significantly higher amount of condensation as a result of the much colder gas flowing through the lines.

2. Know where it comes from

In order to drain the furnace water, you need to know where it comes from. In a high efficiency furnace, condensate is created either from moisture that already existed in the air or the combustion process itself. It’s pretty easy to understand how moisture that was already in the air could cause condensation, but how does the combustion process do it?

3. Regular maintenance

Don’t just clean the lines when they get clogged. Regular furnace repair and maintenance is crucial to keeping it in good working condition. The condensate lines are part of that regular maintenance schedule. You can complete the above step, even if there isn’t a definite clog. It will clean out anything that needs to be cleaned out, and keep the furnace running smoothly.

4. It’s science

Let’s take it back to high school chemistry really quick. Natural gas is a gas mixture of primarily methane. The chemical compound of methane is CH4. That is, one carbon atom and four hydrogen atoms. Water is H20. That is, two hydrogen atoms and one oxygen atom. So, the oxygen in the air and the hydrogen from the methane mix, and that’s where the condensation comes from.

Okay, enough learning, time for action. We know that condensation gets into the unit, but how does it get out?

5. Tilt everything

Your furnace actually should have been installed on a slight tilt – usually the owners manual will indicate this, to ensure that the condensate can drain out on its own. If its not, then you may have to adjust things a little. Your venting and even the furnace itself should be slightly tipped toward the drain to allow for easy drainage. Finally, make sure the drainage tube also tilts down – the condensate cannot drain up.

If the drain is emptying out into the freezing cold, you’re going to be in trouble. You don’t want the condensate freezing on its way out of the drain and blocking future condensate from draining too. Make sure the water has a clean path to freedom.

6. Learn the law

Furnace condensate is acidic. Just one person draining furnace condensate wouldn’t be a big deal. But when everybody is doing it, it can actually change the chemical makeup of water and soil, damaging the environment. As such, some places have put in rules about how to properly dispose of furnace condensate. Often, this involves neutralizing the water before disposal.

7. Disconnect the pressure tube

Locate the tubing that runs from the pressure switch to the heat exchanger. The pressure switch cannot be subjected to any positive or negative pressure, which it would be if you move on to the next step. If you disconnect this tube, you are safe to use the vacuum without concern for damaging your furnace.

8. Suck it out

All condensate drains into a trap. When cleaning the trap, you’ll want to stick the drainage hose from the furnace into the vacuum hose. It may seem counterintuitive, but you do not have to tape around the opening or seal the opening in any way. Simply place the drainage tube into the vacuum hose and turn it on. You will see the water being sucked out of the trap.

Once you’re done vacuuming the trap out, you can reconnect the pressure hose to the heat exchange.

9. Add water

There is an easy and a hard way to do this. The bottom line is that the furnace actually needs a little bit of water in the trap in order to work. Now, you could add some water back into the trap manually by taking off the hoses and opening the whole thing up. Alternatively, you can simply block the end of the drainage hose with something (like your finger), and let the furnace run for a few minutes.

By blocking the drainage hose, you are preventing air from coming in, and water from coming out. A bit of water will build up in the trap after a couple of minutes, and that’s enough to give the furnace the water it needs to run.