A catalytic heater burns fuel gas without a flame by reacting it on a platinum-coated pad, but that reaction only sustains itself once the pad is hot. From cold, the pad cannot light off on its own, so it has to be warmed first. Catalyst pad preheat is that cold-start step: an electric element brings the pad up to light-off temperature before gas is admitted. This guide explains why the preheat is necessary, why it draws a large transient current, and how an RTU sequences and confirms the warm-up before opening the fuel.
Catalyst Pad Preheat in one line: Catalyst pad preheat is the cold-start sequence on a catalytic heater in which an electric heating element warms the platinum catalyst pad to its light-off temperature before fuel gas is introduced. Below that temperature the flameless catalytic reaction will not sustain, so the pad must be preheated first; the preheat draws a large transient electrical current, and a controller sequences the warm-up, confirms the pad is hot, and only then admits gas.
A catalytic heater produces heat through a flameless reaction: fuel gas meets oxygen at the surface of a platinum-coated pad and oxidizes there, releasing heat without a visible flame. Like most catalytic reactions, it only proceeds fast enough to sustain itself once the catalyst is above a threshold temperature, its light-off point. Below that temperature the reaction is too slow to matter, so admitting gas to a cold pad accomplishes nothing useful - the gas simply passes through unreacted rather than lighting off into steady heat.
That is the reason the cold-start problem exists. A hot catalytic pad happily maintains its own reaction, because the heat it produces keeps it above light-off, but it has no way to reach that temperature from cold by itself. Something external has to bridge the gap and bring the pad up to the point where the reaction becomes self-sustaining. Once there, the external help can be withdrawn and the pad carries itself; before there, it cannot start.
Preheating solves this with an electric heating element built into or against the pad. On a cold start the element is energized to warm the catalyst to light-off temperature, and only then is fuel gas admitted so the reaction can take over. Admitting gas prematurely, before the pad is hot, would let unreacted fuel gas flow, which is both wasteful and unsafe, so the whole point of the sequence is to guarantee the pad is ready before any gas is released.
The preheat element is a resistive electric heater, and warming a cold pad quickly takes real power, so energizing it produces a large current draw for the duration of the preheat. This transient is a defining feature of the cold-start: for the minutes it takes to bring the pad to light-off, the heater's electrical demand is far higher than anything it needs once running, since a catalytic heater in normal operation consumes essentially no electricity - the reaction is self-sustaining. The spike is confined to startup.
That transient has to be planned for on remote and off-grid power systems. A site sized only for the tiny steady load of an RTU and a radio can be caught out by the preheat surge, so the power source has to have the headroom to supply it, or the site risks sagging its voltage every time a heater cold-starts. The current draw is significant enough that on a solar or battery site it factors into the power budget explicitly, and staggering the preheat of multiple heaters can avoid stacking their surges on top of one another.
The transient is also useful as a signal. Because a genuine preheat draws a known, substantial current, the controller can watch that draw to confirm the preheat element is actually working. If the element has failed open, the expected current never appears, and the controller knows the pad will not warm and can abort rather than admitting gas to a cold pad. So the very characteristic that makes the preheat demanding - a big, distinctive current - doubles as proof that the warm-up step is genuinely happening.
In an automated installation the cold-start is a sequence the RTU runs, not a manual procedure. The controller energizes the preheat element, waits for the pad to reach light-off - judged by a timed warm-up, by a temperature sensor on the pad, or by both - and only after that confirmation does it open the fuel gas valve so the catalytic reaction can begin. The ordering is strict and interlocked: gas is not admitted until the pad is confirmed hot, because the entire safety and reliability case for the sequence rests on that condition being met first.
Confirmation is what turns a hopeful warm-up into a safe start. The RTU can verify preheat several ways - checking that the element drew its expected current, watching a pad temperature reach the threshold, or requiring both - and it treats a missing confirmation as a reason to abort rather than proceed. An element that failed to draw current or a pad that never reached temperature means the start is unsafe, so the controller closes out without releasing gas and can raise an alarm that the heater failed to preheat. This prevents the dangerous case of fuel flowing to a cold pad that cannot consume it.
Running this in an RTU tied to a cloud SCADA also makes the cold-start visible and manageable from off-site. A heater that fails to preheat at a remote wellsite can announce the failure remotely instead of being discovered as a cold instrument cabinet on the next visit, and the preheat current and pad temperature can be trended to spot an element that is weakening over successive starts. For unmanned sites that rely on catalytic heaters for freeze protection, knowing that a heater actually completed its light-off sequence - or did not - is exactly the kind of assurance remote monitoring is meant to provide.
The flameless reaction that heats a catalytic pad only sustains itself once the catalyst is above its light-off temperature. On a cold pad the reaction is too slow to matter, so admitting gas achieves nothing useful and lets unreacted fuel flow, which is wasteful and unsafe. The pad has no way to reach light-off from cold on its own, which is why an electric element must preheat it first.
The preheat uses a resistive electric heating element, and warming a cold pad to light-off quickly takes real power, so the element draws a large current for the minutes of the warm-up. This is a startup-only transient - a running catalytic heater consumes essentially no electricity because the reaction is self-sustaining. On remote solar or battery sites the surge has to be budgeted for, since the site's steady load is otherwise tiny.
The controller runs an interlocked sequence: it energizes the preheat element and only opens the fuel valve after the pad is confirmed at light-off temperature. It can confirm this by a timed warm-up, by a temperature sensor on the pad, by verifying the element drew its expected current, or by a combination. If confirmation never arrives, the RTU aborts the start and can alarm rather than release gas to a cold pad.
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