ThermoLink vs Tube-In-Tube Heat Exchangers for Pool Heaters

Heat pump pool heaters are becoming more and more popular to have installed in Central Florida.

It’s sometimes tough to distinguish differences between pool heaters because many of the marketing messages focus on benefits, and not on what actually makes one pool heater different from another.

We’ve found one of the key features that separates a good quality heat pump pool heater from a poor unit is the type of heat exchanger used by the manufacturer.

The heat exhanger is what actually does the bulk of the temperature change in a heat pump pool heater. Essentially, water is run across a hot coil, the water picks up heat as it runs across this hot surface, and then is pumped back into the pool. We like to use two analogies:

  1. Firstly, its like taking a hot pan directly off of the oven and running water over it at the sink. This water hitting the pan usually makes a sound you can hear and the water gets so hot that steam comes off of the pan. Its hot to touch that water for a few seconds because the heat from the pan transfers to the water. This is what happens when the water runs across the hot surface.
  2. Secondly, its like sitting in a bathtub and turning on the hot water again after you’ve already been in the tub for a while. Down by your feet, you can feel that hot water mixing in with the colder water, but the whole tub has not yet heated up. You’ll need to keep that hot water flowing into the tub in order for it all to feel comfortable again.This is what its like for the heat pump pool heater to heat your pool.

Most of a heat pump pool heater’s efficiency comes from how effectively it can transfer this heat from the heat exchanger into the pool. That’s why its called a heat “exchanger”. Its exchanging heat from one surface (the coil) to another (the water).


tube-in-tube heat exchanger

Traditionally, heat pump pool heaters have had whats called a “tube-in-tube” heat exchanger. The water flows through a tubed pipe, and on the inside of that pipe is a heat excahnger coil (usually made of an alloy called cupronickel). The water flows between this outer-tube pipe and the inner-tube heat exchanger coil and picks up heat as it flows through it. This was effective at heating the water, but one drawback to this style is the need to really push that water through that tube (it won’t just passively “flow” through that tube).


thermolink heat excahnger

AquaCal and Tropical heat pump pool heaters have been beautifully engineered with a “ThermoLink” heat exchanger. The water flows into the top of heat exchanger assembly from the top, and then uses gravity to flow down to the exit valve at the bottom of the assembly. The water is heated much more passively as it flows like a waterfall through the assembly. Plus, the coil is made from titanium instead of the traditional cupronickel. The cupronickel alloy is much more susceptible to weakening from sanitizers and chemicals found in pool/spa water. Titanium is much longer lasting compared with cupronickel because it is virtually impervious to water-chemistry damage (which is why AquaCal and Tropical units have a lifetime heat exchanger warranty).

Variable-Speed Pool Pumps need ThermoLink

In the past, when single-speed pool pumps were the norm, tube-in-tube heat exchangers were sufficient because the pump would always be running with the same speed (pressure). In modern pool set-ups, we are seeing that two-speed or variable speed pool pumps are the new normal (new regulations will soon make them required by code). These pool pumps aren’t always running at the same “speed” (more accurately they vary the water pressure). Having a pool heater with a regular tube-in-tube heat exchanger renders the benefits of a varaible-speed pool pump useless because the pool pump must keep the water pressure at a high-level in order to push the water through that tube-in-tube assembly. The patented ThermoLink heat exchanger in the AquaCal heat pumps allow the pool pump to ramp itself down to lower pressures, as low as 1560 RPMs. The tube-in-tube assembly has to run at over 2350 RPMs, a 33% decrease in efficiency. This translates to about $25-$94 a month in energy cost that the ThermoLink heat exchanger will save customers compared to tube-in-tube heat exchangers.

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