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Applications
Water, Rinse and Process Tank Heating
Water is the most forgiving liquid to heat and the one most often got wrong, because the failures come from what is dissolved in it rather than from the water itself.
Water is easy until it is not
Clean water carries heat away from a sheath better than almost anything, which is why water heaters tolerate 60 W/in² and beyond where heavy oil is limited to single digits. That makes water heaters compact and inexpensive.
The trouble is what the water contains. Three things account for most water-service failures:
Hardness and scale. Mineral scale deposits on the hottest surface in the tank, which is the element. Scale insulates, the sheath runs hotter, more scale forms. It is the same runaway mechanism as coking in oil. Hard water service needs derated watt density and a cleaning schedule.
Chlorides. Municipal water, well water and cooling tower water all carry chlorides, and evaporation concentrates them. Hot chloride solutions pit and stress-crack 300 series stainless. If a stainless heater is failing early in what looks like plain water, test the water before ordering an identical replacement.
Deionized water. Counterintuitively aggressive. DI water is hungry for ions and attacks copper and many other metals. Use 316 stainless or titanium, not copper.
Where water tanks get heated
- Rinse tanks on plating and finishing lines. Hot rinse improves drying and reduces spotting.
- Parts washers and soak tanks. Usually alkaline rather than plain water; 316 stainless is standard.
- Process water and batch make-up. Bringing water to temperature for a downstream process.
- Freeze protection and holding tanks. Low watt density, long duty, mostly loss replacement.
- Hot water storage and closed loops. Incoloy above roughly 250°F, and where scale is likely.
- Glycol loops. Higher specific heat than oil and far more forgiving, but check the mixture ratio.
Selection by water type
| Service | Typical sheath | Max W/in² | Note |
|---|---|---|---|
| Clean treated water, under 200°F | 316 stainless, Incoloy 800 | 60 – 90 | Copper only in mild low-temperature service |
| Hard or scaling water | Incoloy 800, 316 stainless | 30 – 45 | Derate and plan on periodic descaling |
| Hot water above 250°F | Incoloy 800 | 45 – 60 | Standard for high temperature water and steam |
| Deionized water | 316 stainless, titanium | 40 – 50 | Aggressive to copper; avoid copper entirely |
| Chloride-bearing or cooling tower water | Titanium | 45 – 60 | Stainless pits and stress-cracks |
| Alkaline parts washer solution | 316 stainless | 30 – 45 | The most common washer specification |
| Hot rinse tank on a finishing line | 316 stainless, PTFE-coated | 30 – 45 | PTFE where drag-in from acid tanks is likely |
| Glycol and water mixture | 316 stainless, Incoloy 800 | 40 – 55 | Confirm the mixture ratio; it changes both properties |
Water tank questions
How many kW to heat a water tank?
kW equals gallons times 8.34 times the temperature rise in °F, divided by 3412 times the heat-up hours, then add losses and a margin. For 500 gallons and a 100°F rise in two hours, the heat-up load is about 61 kW; over eight hours the same job is about 15 kW. Heat-up time is the variable with the largest effect on cost. The sizing calculator includes the loss estimate.
Why does my water heater element keep scaling up?
Because the element is the hottest surface in the tank, and dissolved minerals precipitate on the hottest surface. The higher the watt density, the faster it happens. In hard water, derate the watt density to spread the same kilowatts over more surface area, plan on periodic descaling, and consider Incoloy, which tolerates the resulting hot spots better than stainless.
Can I use a copper element in a water tank?
Only in clean treated water at modest temperature. Copper conducts heat well and is cheap, but it corrodes in deionized water and in the presence of chlorides, and it is unsuitable for almost any chemical solution. In anything other than clean low-temperature water, specify 316 stainless or Incoloy.
Why did a stainless heater fail in plain water?
Almost always chlorides. Municipal water, well water and especially cooling tower or evaporating water carry chlorides that concentrate over time, and hot chloride solutions pit and stress-crack 300 series stainless. Test the water. If chlorides are present, titanium is the replacement.
Should I use Incoloy or stainless steel?
316 stainless is the economical default for water under about 250°F with reasonable water quality. Incoloy 800 costs more but has better high-temperature strength and oxidation resistance, tolerates scale-related hot spots better, and survives brief dry-fire conditions that would destroy stainless. Above 250°F, in hard water, or where dry-firing is a realistic risk, Incoloy is worth the difference.
Does covering the tank really save that much?
Yes, on a hot tank. Evaporation from an open water surface removes far more energy than conduction through an insulated wall, so a cover often cuts the maintain load by half or more. It also reduces make-up water, which reduces the rate at which chlorides and hardness concentrate in the tank — so the lid extends heater life as well as saving energy.
Send the tank volume and the water
Municipal, well, DI or a solution, plus hardness if you know it. Water quality decides the sheath and the watt density.