If you have ever stood in a cold shower, you can appreciate that sizing is critical to your home hot-water system.

With a tank-type water heater, the rule of thumb has been to give a 40- or 50-gallon heater to the "average" home, and a 75- or 100-gallon heater to larger or high-end homes. But even those can be inadequate in active households with the latest whirlpool tubs and multi-head showers. Once you run out of hot water, you’re done – it takes a long time for the heater to "recover" and be ready to service you again.

Sizing a Paloma Tankless system is quite straightforward. With a Paloma Tankless, you need to calculate peak demand – which is Gallons per Minute at the busiest time of day. And then you need to factor in temperature rise between inlet water and your showering temperature (assuming that your peak demand comes from the bathroom, which is usually true).

This is very easy to calculate once you know how many gallons of water per minute your fixtures use. Most basic showerhead fixtures use 2.5 gallons per minute at around 104 ^o. If you are planning a modern bathroom with multi-head shower fixtures, see the product spec sheet or get advice from your plumber.

Once you know your Peak Requirement for hot water in Gallons Per Minute, then you need to check which Paloma Tankless Series can supply what you need in the dead of winter (when temperature rise will be greatest). If you are not sure about your local conditions, you can do a good approximation using 40-degree inlet water temperature in northern climes and 50-degree inlet water in the sun belt. See the table below.

Paloma Tankless Sizing Guide - Gallons Per Minute at 104 degrees F

	Digital Tankless						Legacy Tankless
System Type	Multi-unit	Multi-unit	Standalone	Standalone	Standalone		Standalone
Model	7.4 Series x 3	7.4 Series x 2	7.4 Series	6.6 Series	5.3 Series		PH-24
Northern Winter (40 degrees F)	15.6	10.4	5.2	4.6	3.6		4.5
Southern Winter (50 degrees F)	18.5	12.3	6.2	5.4	4.3		5.3
Summer (70 degrees F)	29.4	19.6	9.8	8.7	6.8		8.4

The Guide gives an approximation of system outputs at showering temperatures. This performance can be achieved by setting your Digital Controller at 104 degrees except in the Summer Case, where it is necessary to set the Controller at 116 degrees and mix in cold water. This is because peak performance is achieved when the temperature rise is 45 degrees or more.