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Since 1984

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Serving the Lubbock Area

For Faster Service Please Call!



JD's Prompt Plumbing, Heating & Air Conditioning Blog

How to Protect Your Furnace from Ice


While we don’t tend to have long stretches of extreme cold in our area, extreme weather does sometimes happen. In fact, one of the longest stretches when the temperature stayed below freezing in Lubbock—for an entire week!—was just a few years ago. And when temperatures are that cold, even if it’s not for quite that long, you could be at risk of a frozen furnace.

You might be surprised to hear that an iced-up furnace is even possible. How could a furnace freeze? Where does the ice come from? We’ll explain all about it, including what you can do to make sure it doesn’t happen to you.

Condensing Furnaces

Once upon a time, gas furnace efficiency was around 70-80%. That means that somewhere around a quarter of the energy used to operate the furnace was simply lost rather than being turned into heat! What a waste, and what an unnecessary cost. While ordinary gas furnaces are somewhat more efficient than that now, the real advance was the invention of condensing furnaces.

A traditional gas furnace lost so much of the energy it used because it vented the exhaust while it was still very hot. But by retaining the exhaust for longer, allowing it to cool more before venting, a condensing gas furnace can actually utilize much more of that heat and thus much more energy. They can be up to 98.5% efficient!


Imagine pouring some very hot water into a pot and putting the lid on. Leave it alone to cool down. When you take off the lid, it will be covered with droplets of condensation. That’s what happens inside the condensing gas furnace, because that exhaust is not vented until it cools down. This means the furnace must have a place for that moisture to go: a condensate pipe.

This condensate must be safely conducted away from the furnace, and most of the time, the condensate pipe leads outdoors. The potential problem occurs if, instead of thoroughly draining, water ends up pooled inside the pipe. Then, freezing temperatures can turn that water into ice, blocking the condensate drain.

Make Sure Your Condensate Will Drain Properly

How can you be certain that a frozen condensate line won’t happen to you? First, the line must be sloped enough that the water will run out. Second, the line must be supported underneath rather than hanging in space. Without support, it could sag, leading to a low spot where water will pool. Third, the line should be as short and direct as possible. And fourth, the line should exit your home well above the level where any snow or ice could accumulate on the ground.

If your condensate line becomes blocked with ice, it won’t just cause condensation to back up. Because that would create major problems in the furnace, it will actually shut down completely to prevent any damage. So a frozen condensate line will quickly turn into a completely non-working furnace. Don’t let this happen to you!

Do you have any concerns about your condensate line? If you’re not sure it’s sloped enough, if it doesn’t have support underneath it, if it’s long or convoluted, or if it exits your home very low to the ground, you should be concerned. Have it checked by a qualified professional before you end up needing major furnace repair in Lubbock, TX

JD’s Prompt Plumbing, Heating & Air Conditioning serves the Lubbock area. Contact us for all your furnace maintenance and repair needs.

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