Every year, winter settles in, the temperature dips, and once that outside air hits 32°F, the phone starts ringing. “My steam coil froze — please get out here ASAP and get me a new one”. It’s predictable. It happens every single year. And with 32 people in the Merlo Energy division, I can guarantee that every one of them has taken some version of that call — sometimes multiple times in the same week. Freezing coils are common, but not unavoidable. Let’s dig into what’s really going on and how to prevent it.
What a Frozen Coil Looks Like
If you’ve ever seen a coil tube with a long split and a slight bulge, you’ve seen the classic telltale sign of freezing.
Water expands as it shifts from liquid to solid. When that happens inside a sealed tube, pressure builds until the metal gives out. Once things warm up, the ice melts, and you’re left with a leak — maybe a slow drip, maybe a gusher, maybe live steam. Regardless of severity, it all points to one thing: water was trapped inside the coil, and cold air froze it. The most reliable way to prevent this is simple: remove condensate as fast as it forms.
Why Steam Coils Freeze — and What to Do About It
When water turns into ice, it expands. Inside a coil, that expansion creates pressure the tube simply can’t withstand—resulting in a split along its length. Once temperatures rise, the ice melts, and you’re left with leaks. Sometimes it’s minor; other times, it’s a full-blown steam release.
The root cause? Condensate trapped inside the coil. As steam gives up its heat, it becomes water. If that water isn’t removed quickly, cold air will freeze it.
Let’s go straight to the root causes we see in the field every winter — and, more importantly, the solutions that actually work.
1. Failed Steam Traps
If your steam traps fail closed on a coil, the condensate stays put — and you will freeze the coil. Routine trap maintenance isn’t optional in cold climates; it’s protection.
A steam trap management program will:
- Identify failed traps
- Prioritize repairs
- Reduce freeze risk across your system
If you haven’t tested traps lately, that’s step one. Find your failed traps and fix them. Download the brochure on Steam Trap Management.
2. Modulated Steam Control Valves
A modulating steam valve can unintentionally create the perfect environment for what we call equipment stall — steam condenses, pressure drops, and condensate can’t drain. Once drainage stops, freezing isn’t far behind. You can eliminate stall risk by adding one or more of the following:
- A vacuum breaker
- A safety drain
- A positive pressure system
- A condensate pump
Any one of these helps. The right combination eliminates the problem entirely.
3. Coil Design Issues
Tube diameter too small? Coil too long? Both increase the likelihood of trapped condensate — especially under part-load operation.
Choosing the right manufacturer matters. Work with teams who understand freezing, flow dynamics, and proper coil design. Armstrong International, for example, engineers coils specifically to reduce freeze risk.
Explore Heat Transfer Coils & Equipment from Armstrong International.
4. Improper Piping
Even the best-designed coil will freeze if the piping is wrong. Incorrect pitch, missing components, poor trap placement — any of these can leave condensate stranded.
If you’re unsure, compare your setup with established guidelines from manufacturers and industry standards.
Read this educational article on how to trap space heating equipment from Armstrong International.
Download the attached Installation, Operation, and Maintenance Instructions Manual from Armstrong International.
Prevent Frozen Coils Before They Happen
While frozen coils tend to fail in familiar ways, the factors that lead to those failures can vary. With the right design, proactive maintenance, and targeted system improvements, you can keep your coils — and your operation — running reliably through winter’s harshest conditions. Don’t let the harsh winter expose vulnerabilities in your system. Schedule a steam system assessment with Merlo Energy and keep your operation safe, efficient, and freeze‑free all season long.
About Erich Knemeyer | Technical Specialist at Merlo Energy
With over 33 years of experience in steam, condensate, and hot water systems, Erich Knemeyer possesses extensive knowledge and expertise in optimizing heating system efficiency. He holds a BS in Engineering Physics from Miami University in Ohio and has dedicated his career to assisting customers in troubleshooting their steam and heating systems. Currently, Erich collaborates with engineers and contractors, providing support in design development and the startup process.
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