We will start our sizing exercises with homes where less than two bathrooms are present. You will see tables for gas-fired, electric, and oil-fired water heaters. The number of bedrooms in our sample homes can range from one to three. You will have to use the chart to size a water heater for the examples given. Let’s start with a gas-fired water heater. The house we will size it for will have two bedrooms and one bathroom. What size water heater is needed (Fig. 7.1)?
All you have to do is scan the table for the answer to sizing question. Look under the heading for two bedrooms and run down to the column that lists storage. You will see that a 30-gallon water heater is the minimum size recommended for the application. You will also note that the water heater will recover fully in one hour. Personally, i’d probably up the size of the
|
Number of bedrooms |
1 |
2 |
3 |
|
Storage capacity (gallons) |
20 |
30 |
30 |
|
Input in Btuh |
27,000 |
36,000 |
36,000 |
|
Draw (gallons per hour) |
43 |
60 |
60 |
|
Recovery (gallons per hour) |
23 |
30 |
30 |
|
Number of bedrooms |
1 |
2 |
3 |
|
Storage capacity (gallons) |
20 |
30 |
30 |
|
Input in Btuh |
2.5 KW |
3.5 KW |
4.5 KW |
|
Draw (gallons per hour) |
30 |
44 |
58 |
|
Recovery (gallons per hour) |
10 |
14 |
18 |
|
Number of bedrooms |
1 |
2 |
3 |
|
Storage capacity (gallons) |
30 |
30 |
30 |
|
Input in Btuh |
70,000 |
70,000 |
70,000 |
|
Draw (gallons per hour) |
89 |
89 |
89 |
|
Recovery (gallons per hour) |
59 |
59 |
59 |
heater to 40 gallons, but by code in my region, a 30-gallon tank is all that would be required.
Now, suppose we had the same house but wanted to put an electric water heater in it? What size would we use? Refer to the table in Figure 7.2 to find your answer. In this case, the storage capacity for an electric heater is the same as that required of a gas-fired heater. A 30-gallon tank is all that is needed. But, look at the recovery rate for the electric heater. It’s about half as good as the recovery rate for a gas heater. This could be good reason to upgrade the heater to something larger or more powerful.
Let’s consider an oil-fired water heater. The basic table (Fig. 7.3) is the same, in terms of use. Again, using the same scenario, what size oil-fired heater would be needed? You will find that a 30-gallon tank is, once again, adequate. Check out the recovery rate. It’s great. As you can see, sizing water heaters with the tables provided here is truly easy.
