Gas and oil pool heaters
How does a gas pool heater work?
A typical gas-fuelled pool heater uses natural or propane gas as the heating fuel. The pool water enters through one port of the front water header, then through the nine heat exchanger, and then out of the other port. Like with most of the pool heaters, water go through at least four of the tubes and picks heat on each pass before leaving the heater. The exchanger tubes are made of copper due to its excellent heat conductivity, there by heating effectively the water. The tubes have fins to absorb heat even more efficiently and are topped with sheet metal baffles to retain the heat. However, improper water chemistry can easily attack this soft metal and dissolve it into the heated water. There is a flow control assembly on the front header. This spring-loaded valve is pressure sensitive, designed to mix cool incoming water with heated outgoing water to maintain the temperature. Temperature control is achieved by flow regulation rather than direct temperature regulation. This prevents condensation and other problems that greater temperature differentials would create. When water temperatures are over 46°C (115°F), minerals suspended in water deposit in the heat exchanger. The other major component of the gas-fuelled heater is the burner tray. This assembly can be disconnected from the cabinet for maintenance or inspection. Depending on the size of the gas pool heating device, there will be 6 to 16 burners, the last one having a pilot mounted on it. Individual burners can be removed for replacement. The combination gas valve regulates the flow of gas to the burner tray and pilot and is itself regulated by the control circuit. Gas-fuelled heating devices are divided into two categories based on the method of ignition. They are millivolt or standing pilot heaters and the other being electronic pilot heater.
The milli volt or standing pilot heater
This type of heater has a pilot that is constantly burning. The heat of the pilot is converted into a small amount of electricity (750 milli volts) by a thermocouple, powering a number of switches. Together, the control switches constitute a control circuit. When electricity passes through the entire control circuit, the main gas valve opens and the burner tray gets flooded with gas. The gas is then ignited by the pilot. The temperature of a pilot flame is more than 600°C (1100°F).
Electronic ignition heaters
An electronic spark ignites the pilot when a gas-fuelled pool heater with electronic ignition is turned on. This in turn ignites the gas burner tray in the same manner as described previously. In all other respects, these pool heaters operate the same way as those already discussed. Where the control circuit on the standing pilot heater is powered by milli volts, the electronic ignition heating device is controlled by the same kind of circuit but is powered by 25 volts AC. Regular line current at 120 or 240 volts is brought into the heater and connected to a transformer that reduces the current to 25 volts. This voltage is first routed into an electronic switching device called the IID (intermittent ignition device), which acts as a pathway to and from the control circuit. From here the current follows the same path through the same control circuit switches as described previously. When the circuit is completed the current returns to the IID, which sends a charge along a special wire to the pilot ignition electrode creating a spark that ignites the pilot flame. The IID simultaneously sends current to the gas valve to open the pilot gas line. When the pilot is lit, the heat generates a current that is sensed by the IID through the pilot ignition wire. This information allows the IID to open the gas line to the burner tray, which is flooded with gas ignited by the pilot.
Natural versus Propane Gas
There's not much difference in heaters using natural gas and those using propane gas. The gas valve is clearly labelled Propane. Because of different operating pressures, the gas valve is slightly different although it looks the same as a natural gas model, as are the pilot light and the burner tray orifices. The heater case, control circuit, and heat exchanger are all the same as for a natural gas model. Most manufacturers make propane heaters in standing pilot/milli volt models only. Natural gas is lighter than air and will escape if the burner tray is flooded with gas but not ignited for some reason. The odour added to natural gas can be detected if you are near by. With propane, however, the gas is heavier than air and if it floods the burner tray without being ignited it tends to sit on the bottom of the heater. Because it remains undissipated and cannot be detected by smell, if it ignites suddenly, it will do so with violent, explosive force. Rarely is the heater itself damaged-the explosion takes the line of least resistance, which is out through the open front panel. Never position your face in front of the opening and always use the safety checklist before trying to detect any thing wrong in the system.
And what are the pros and cons of gas?
One advantage of a gas pool heater is that it gives you the most options in terms of manufacturers, models, and sizes. Gas pool heaters are plentiful, with numerous companies offering several different makes, making comparison shopping easy. Another advantage of gas pool heaters is that gas is one of the cheapest kinds of fuel you can buy. Also, the power of gas ensures quick swimming pool water heating, giving you maximum performance. But a big disadvantage of gas is that some areas do not distribute this kind of fuel, meaning that some swimming pool owners do not have this option available to them at all. Another drawback is that the cost of using natural gas for your swimming pool can average out to €150-€300 per month. Also, the mechanism creates a hot flame that reacts against the heat exchanger, diminishing its life. This is a big disadvantage, as the heat exchanger is one of the most important components of a natural gas pool heater. Finally, although it is the cleanest fossil fuel, natural gas will still contribute to the greenhouse effect.
What about oil-fuelled heaters?
Oil pool heaters are not very common, and are designed identically to gas pool heaters but they burn diesel fuel instead of gas. This type of fuel has the advantage of being the most readily available, and can also be stored in drums on your property. But oil does have an odour, so these types of pool heating devices are best located as far away as possible from the swimming pool and recreation area. Also, the cost of burning fuel oil can vary depending on geographical location, but it is generally the most expensive fuel to use.