I realize this sounds stupid, but theres logic behind my question. Do i really need to have a bigger heater for a bigger pool. The heated water flow is restricted by the return jet regardless of the size of the pool. The heat pump heater can only heat the water to a design temperature as it flows and that flow is restricted by the pump pressure and the return jet. Any comments?
Pool heater
- Thread starter ctmcusn
- Start date
A larger heater heats the water faster. Because the heat exchanger is larger, it heats more water at a pass through it than a smaller capacity, in BTU, heater. And, it overcomes the heat loss off the surface of the vessel better.
Unless you have a very old pool that has only one return, usually 1" plumbing, that can't have the flow, any pool built in the last 50 years will have enough flow to use the BTU output of a large heater. And with a VSP, even that old pool would heat faster with a 400K BTU heater.
Bill1974
Well-known member
- Jun 18, 2014
- 659
- Pool Size
- 32000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60 Plus
I can see your logic but it's missing some consideration or factors. In a particular situation your statement could be correct, but it's only certain conditions.
If your pool is already at the desired temperature the heater would only need to be as large as the heat loss to maintain the temp. To increase the temp it would be impossible or extremely slow to raise the temp.
If the return flow were restricted that the heater would constantly hit it's high limit and it would likely cycle the heater on and off to any early demise. Usually there is a degree or two delta between the set point and a drop before the heater should kick back on. With the mass of the water in a pool this difference could be a fraction of a degree and not be an issue unless the flow is a really low.
Unless the pool is really well insulated and indoors, a larger pool will always need a larger heater. Outside pools heat is lost to the ground, to the air and from evaporation. Usually the ground is the smallest factor. Air would be the next largest factor and if it's windy it's even more of an effect. Evaporation is the largest typically, it take a lot of energy to change water to vapor and that energy is taken from the pool water. To evaporate 1 galloon of water takes about 9.3K btu. Evaporate an inch of water out of a 20 x 40 foot pool and 4.500,000 btu's of heat left the pool cooling the water in the 16 degrees. Really the water would not drop that much because the solar gain. (I think I math is correct, but I could have messed something up)
If your pool is already at the desired temperature the heater would only need to be as large as the heat loss to maintain the temp. To increase the temp it would be impossible or extremely slow to raise the temp.
If the return flow were restricted that the heater would constantly hit it's high limit and it would likely cycle the heater on and off to any early demise. Usually there is a degree or two delta between the set point and a drop before the heater should kick back on. With the mass of the water in a pool this difference could be a fraction of a degree and not be an issue unless the flow is a really low.
Unless the pool is really well insulated and indoors, a larger pool will always need a larger heater. Outside pools heat is lost to the ground, to the air and from evaporation. Usually the ground is the smallest factor. Air would be the next largest factor and if it's windy it's even more of an effect. Evaporation is the largest typically, it take a lot of energy to change water to vapor and that energy is taken from the pool water. To evaporate 1 galloon of water takes about 9.3K btu. Evaporate an inch of water out of a 20 x 40 foot pool and 4.500,000 btu's of heat left the pool cooling the water in the 16 degrees. Really the water would not drop that much because the solar gain. (I think I math is correct, but I could have messed something up)
How about some actual facts about things like pool size, flow rates, water temp unheated, water temp heated, pump, filter, surface area, air temp, covered or uncovered, kept heated or heat on demand etc.?