3 Enemies of Hot Tub Heater Elements
Hot tub heater elements are similar to the electric immersion elements used in household hot water heaters and washing machines, with a few important distinctions. Hot tub water chemistry tends to vary and it swings widely when 4 people jump into the tub. Spa heater elements are also subject to issues from low water flow or air inside the heater chamber, and all of these variables can lead to a shorter spa heater element lifespan.
Air Bubbles and Air Pockets
The main enemy to all spa heater elements, besides low water flow, are air bubbles & air pockets that can reduce element life. Air that comes in contact with the elements allows the outer sheath to rapidly heat unevenly, which breaks the protective sheath and exposes the filament. Low flow heaters are mounted vertically, so the bubbles are constantly exiting the chamber without entrapment. Tube heaters like the Laing design do not trap bubbles, so they can be bent into bizarre shapes, & even lay on the floor.
Spa pumps are designed to be flooded & should not leak air or be allowed to cavitate by drawing in air, then sending the air through the hot tub heater. Ozone injectors should not be placed before the heater, which would reduce heater element lifespan and confuse hot tub heater sensors.
Bad Hot Tub Chemistry
Poor hot tub water chemistry is damaging to spa heater elements, particularly low pH and Alkalinity and high hardness levels. Additionally, fill water that is naturally high in salt, lime and calcium can also promote a slower, but still premature death. Corrosion is an etching and rusting effect that happens to ferrous metals (made with iron). As water becomes acidic (low in ph) high in TDS or overly chlorinated, corrosion is accelerated and your heater element is most at risk.
Hard Water Problems
Hot tubs in hard water areas, or those that are filled from an onsite well can have trouble with metals and minerals. Lime & calcium can naturally collect on a heater element surface, forming a white coating. This layer of scale will slow heat transfer, resulting in lower efficiency, longer heater run time, and a higher internal element temperature. The plaque buildup will not let heat escape efficiently, and in time the element will essentially cook itself to death. Use a Pre-Filter to fill your tub with pure water, a lot cheaper than 300 gallons of mineral water!
High Flow Heaters
No matter what shape the heater is, a high flow heater (typical name flow thru) utilizes a hi-watt density element (hwd) that requires a minimum 22.5 gpm to keep it cool. A typical 2 speed spa pump provides this minimum flow at low speed. When flow is restricted below 22.5 gpm, the element runs hotter than designed, and the spa heater element life is shortened. Bath and Jetted Tub heaters are always high flow and use the high density element (hwd), as bath pumps always exceed 25gpm. HWS heaters come in many shapes like Flow Thru, Tee, L-shape & Canister. You will not find hot tub parts catalogs separated into high flow & low flow heaters, but you do need to know this info to be a true hot tub expert.
Low Flow Heaters
Low flow heaters are designed for vertical mount operation. The exception is the tube or Laing spa heaters we supply. Either design is made with a much longer, cool running low watt density element (lwd) These heaters & elements are made to operate on flows greater than 9+ gpm. It makes perfect sense that low flow heaters are paired with low flow circulation pumps, like the Waterway, Laing & Grundfos spa pumps, which provide minimum 9+ gpm with a spa ozone injector. Low flow heaters contain more material & labor, this is why they cost more money.
Some repair techs either don't know, or try to save money by placing a high flow heater into a low flow circulation plumbing system. It actually works for a while, then the element burns out, along with plastic parts, piping & wires. Be sure and confirm that you are using the correct heater for your spa.