The one component nobody can see
A condensate heat trace is a low-wattage heating cable running along the drain line, usually taped on and then covered with insulation. It is completely invisible once installed. It has no indicator light, no alarm, and no symptom of its own when it fails. The first sign that it stopped working is ice somewhere else entirely — on the coil, on the floor, or backing up into the drain pan.
That makes it one of the small number of components genuinely worth testing on a schedule rather than waiting for a fault, because there is no other way to know.
How the line is supposed to work
Water leaves the evaporator pan during defrost at a few degrees above freezing. It has to travel out of a sub-freezing box, through whatever space lies between the box and a drain, and reach that drain before it loses those few degrees. On a freezer that journey is entirely hostile: the first section is inside a 0°F box, the next section may cross an unheated store or run near an exterior wall.
Three things get it there:
- Heat trace adding warmth along the cold run.
- Insulation over the cable, keeping that warmth in the pipe rather than donating it to the room.
- Continuous fall so the water keeps moving. Moving water has far less opportunity to freeze than standing water.
Lose any one of the three and the line blocks at the coldest or flattest point.
Where they actually freeze
Almost always at a predictable spot, and once you know where it is you can stop guessing:
- At the penetration where the line leaves the box, because that is where the cable is most often damaged during installation or a later repair.
- At a sag. Water stands in the low point, freezes there first, and the blockage then grows in both directions.
- At the trap, if the trap is somewhere cold. A trap holds water by design, so a trap in cold space is a guaranteed freeze point.
- Where the insulation stops. Often the cable and insulation were run neatly for the first few feet and the last section was left bare because it was awkward to reach.
Clearing it without making it worse
If you need the box working before a technician arrives: warm the line gently along its length with warm — not boiling — water poured over the outside of the pipe, or with a hair dryer at a distance. Never with an open flame, and never by forcing a rod into a line you cannot see the far end of. PVC drain line splits easily when cold.
Understand that this buys you days at most. Nothing about why it froze has changed.
The permanent fixes
In order of how often they are the right answer:
- Replace the heat trace cable and insulate it properly along the whole cold run, including the awkward last section.
- Correct the fall — re-hang the line to remove sags and give it continuous slope.
- Move the trap into warm space if it is sitting somewhere cold.
- Reroute the line if a substantial length runs through genuinely cold space such as an exterior wall cavity or an unheated dock. Sometimes a shorter path to a different drain is both cheaper and permanently reliable.
Why this matters more in this region
Drain lines in Greater Boston routinely run through spaces that spend three months of the year below freezing — unheated back halls, loading docks, exterior wall chases in older buildings, and basement rooms with no heat. A drain configuration that would be fine in a milder climate fails here every January. If your line freezes seasonally and reliably, the routing is the problem and no amount of cable replacement will fully solve it.
Questions we get asked
How do I know if the heat trace is working?
A clamp meter on the cable will show current draw when it is energised. Some cables are self-regulating and draw more in cold conditions, less when warm, so a low reading on a warm day is not necessarily a fault. Zero current is.
Can I wrap the line in insulation and skip the heat trace?
No. Insulation slows heat loss, it does not add heat. Water sitting in an insulated pipe in a 0F freezer still freezes, just more slowly. In cold space you need both.
The line only freezes in deep winter. Is that still a fault?
Yes. It means the heat trace or the insulation is marginal, or part of the run is exposed to outdoor temperatures it was not designed for. A line that is fine in November and blocks in January will keep doing that every year and will get worse as the cable ages.