Question

What size heater will be required to heat the water in a swimming pool from

70°F to 72 °F in 1 hour if the appliance is 100% efficient and the pool holds
20,000 gallons of water?
A. 166,000 Btu/h
B. 332,000 Btu/h
C. 86,000 Btu/h
D. 224,000 Btu/h


Ps. the answer is B but i want an explanation on how to work through the problem

Answer 1

B

Explanation:

the British thermal unit (BTU or Btu) is a unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

and it is outdated. your teacher and the manufacturer should use joules as metric.

1 BTU ≈ 1055 joules

anyway, so, the solution has several parts.

we need to find how many pounds of water are in a gallon.

and then multiply by the amount of gallons (20 000) and the amount of degrees (2 from 70 to 72).

and after a little search on the internet we get

1 gallon of water = 8.34 pounds

so, we need to warm

20000×8.34 pounds of water by 2 degrees F.

that is

20000 × 8.34 × 2 = 333,600 BTU

if we use only the rounded value of pounds per gallons (8.3), this would be

20000 × 8.3 × 2 = 332,000 BTU

so in any case, B is the right answer (as being the closest to the real result), which is the situation with any size classification of devices : reality is somewhere close by, but never meets the exact specifications.