What Is a P-Trap, Its Purpose, and How It Works?
Even if you aren’t a plumber by trade, you’ve probably seen the u-shape piece of piping under your kitchen or bathroom sink. You may see this with your Furnace or AC unit. This is a specific piece of plumbing equipment called a P-trap, and it is a necessary part of your home’s plumbing system.
A P-Trap serves a very important purpose on an A/C unit. When moist air hits something cold, the water condenses out of the air and collects on the cold surface. Air Conditioning units pull A LOT of water out of the air. That is why in the summer, your car drips water. All air conditioners have a special drain for this condensation.
A/C units (like mine) have negative air pressure inside them when running. What this means, air is being sucked through the air conditioner instead of blown through, so the inside of the air conditioner is at a lower pressure than the outside air. This presents a problem for the condensation drain. Since the Air Conditioner is at a negative pressure relative to the outside air, the outside air will rush into the air conditioner through any openings (the condensation drain, is an opening). On my A/C the air rushing in through the condensation drain preventing the water from exiting through the drain. So water was building up in our A/C unit and when it would turn off “Woosh…” All that water would pour out of any hole it could find!
There are some simple ways you can tell if the drain line in your house is being run and draining correctly. First, the coil that your primary drain line is running off of needs to be at a downward angle allowing the water from the coil to drip into the drain line. Every drain line also needs a “P-Trap”. If you look at the picture below, it will show you what an HVAC p-trap looks like. The p-trap creates an airlock which then forces the water down the pipes and drains properly.
So why is a P-trap part of your plumbing? There are some reasons:
- Effectively drains condensate in a variety of hvac systems
- Easy access for cleaning
- Fast and easy installation
- Clear cleanable trap
- Plumbing codes require a P-trap be installed anywhere there is an open drain line that expels wastewater into a drain waste-vent system
- The P-trap traps solids that can clog the drain
- The P-trap stops air or gases from backing into your home through the drain line
Why Is My Furnace Leaking Water When the AC Is On?
Although this sounds like one of the worst issues that could happen, it is usually one of the easiest problems to fix and avoid. By making sure you are on an annual maintenance plan, you can eliminate the stress and costly repairs that can come from neglecting your heating and cooling equipment. Making sure you have a ClearView P trap installed can save you money as well.
Condensate Drainage in Gas Furnace
High efficiency (or 90%, or condensing) furnaces use a set of two heat exchangers in order to retrieve more heat from the combustion products than their mid-efficiency counterparts. Because of this, they generate flue gases much colder than those of a mid-efficiency or natural draft unit. This not only completely changes the way the furnace has to be vented but also, and it’s what we’ll focus on, a lot of condensates is generated. This water comes from two sources: moisture which was already present in the combustion air, and the combustion process itself, as the hydrogen atoms from the natural gas molecules (methane, CH4) combine with oxygen to form water. Now as technicians you don’t need to know this part but if you’re a bit into chemistry, here’s the basic chemical equation: