Water heaters in the Yucatan

There has been a lot of discussion on several on-line forums about water heaters and problems. Most of the information they discuss is correct in some details, but completely wrong in others. There are 4 ways to heat water here, solar, electric with tank, gas with tank and gas on demand. Solar heating is a subject all to itself and electric heaters here are too costly to run. So I will talk about the other two.

Tank heaters are pretty basic and just about every home in the USA or Canada has one. Cold water comes in one line filling the tank and hot water exits via another line. The tank is heated by a burner of propane underneath just like boiling water for spaghetti. Except in this case there is a thermostat to control the water temperature. When the water temp drops the thermostat opens the gas and the pilot light turns the burner on, keeping the water at the set temperature. Pretty basic and simple, you will also see a big bolt on top of the tank, this is a sacrificial anode. The anode is designed to corrode first, rather than the tank, but I would be willing to bet no one has ever checked to see if it is corroded beyond serviceability and the tank is corroding instead. You also have a drain tap on the side. This drain is there to de water the tank and get rust and scale particles out. This should be done at least once a year.  If you open the drain and only a trickle comes out you have waited way to long and the bottom of the tank is full of debris. The problem with tank heaters, is they keep a store of water hot ready to use at all times. This take a lot of propane over the course of a year and the bigger the tank the more it is going to burn.

It is on demand water heaters that create most of the confusion and they are made to look like tank heaters a lot of the time. Which really confuses things. An on demand heater ( Linea de Paso) is a series of coils or other method of allowing water to pass through, while a propane flame heats the coils or flow through device. In the USA or in Canada homes that have these systems are pressurized and as such for the most part have a pressure sensor in the unit. The pressure drops when you open the hot tap and the burner lights off, heating the water. However, and this is important, in the Yucatan, most Mexican homes do not have pressure water and rely on gravity for water pressure. Therefore, most units here are not activated by a pressure drop. Bosch being the exception and do require pressure and need a special pump to supply it. They are the exception not the rule. The rest of the units rely on a temperature drop to turn on the burner. A TEMPERATURE DROP!!! They are controlled by a thermostat. If you have one and do not believe me, leave the hot water tap off and go play with the thermostat. Dial it hot and it will light off.  Dial it cold and it will shut off. Notice it worked without a pressure change. That is because it is controlled by a thermostat. But the thermostats need careful adjustment. Say you set the thermostat so that it turns on when the water drops to 25 degrees C, as it passes the coils. The thermostat does not have temperature markings, so you won’t actually know the actual temp. But say it is 25 degrees anyhow. Now think of a nice sunny day and the exposed water lines on your roof and how about your tinaco if it is a black one. The water maybe warmer than 25 degrees to begin with and the boiler will not fire up. You may want hot hot water for some reason but you are not going to get it. The on demand systems are not designed to give you scalding hot water, when you want it. They are designed to give you enough hot water for normal applications like washing dishes or having a shower. In fact if they are adjusted right you won’t need the cold tap. Sure you can dial the thermostat up, but what you don’t want to happen is for the plates or coils to get so hot that the water turns to steam when it passes through. Sure it will be hot but the evaporative process will leave a lot of saro behind plugging things up.

Speaking of saro (the build up of minerals in the heater) the easy way to figure if the build up is an issue, with a demand system,  is water flow. If the hot flow hasn’t change then things should be fine. If however, the flow is reduce, it is probably time to flush all your piping with a mild acid solution, as your hot water lines will also be plugging up. Remember half the diameter, results in 1/4 the flow. Water lines from tank heaters also get a build up of saro and need to be cleaned as well.