Hi! When running your pool heater is it better to run your pool pump on a faster speed or lower speed?
When running pool heater-
- Thread starter Paigez0215
- Start date
Most heaters will have a flow switch that will prevent them from running with too low / no flow. Mine does, and with my variable speed pump I have one of the speeds set where the heater runs best. Too low of a flow and I find that the no-flow switch trips, or the heater hi-limit (overheating) switch can trip, but I don't want to run at full speed either, due to the higher cost of running the pump.
With variable, I find it's about finding the sweet spot given the specific equipment
With a 2 speed, if the heater works on low, you should be good to go.
One note - It's more efficient from a heat transfer perspective to run the heater with high speed, but depending on your electricity rates, that may not be worth the extra cost to do so (gas cost vs. electricity cost).
With variable, I find it's about finding the sweet spot given the specific equipment
With a 2 speed, if the heater works on low, you should be good to go.
One note - It's more efficient from a heat transfer perspective to run the heater with high speed, but depending on your electricity rates, that may not be worth the extra cost to do so (gas cost vs. electricity cost).
- Jul 21, 2013
- 55,419
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
I don't think pump speed makes a material difference on heater performance as long as the pump speed is fast enough to activate the pressure switch in the heater.
The heater puts out constant amount of BTU's. The BTU's will be transferred to the water and heat the pool with whatever water flow there is.
Note that some heaters also have a maximum flow rate and water flow above that rate can prematurely wear out the heat exchanger.
The heater puts out constant amount of BTU's. The BTU's will be transferred to the water and heat the pool with whatever water flow there is.
Note that some heaters also have a maximum flow rate and water flow above that rate can prematurely wear out the heat exchanger.
I think you're correct. Based on a quick Google search, heat loss in a pipe doesn't consider flow rate as a factor so it shouldn't affect the efficiency of the system according to this formula:
Q= 2 * (pi) * k * L(T1-T2)/ [ln(r2/r1)]
where k= the heat transfer coefficient of the pipe material,
T1= the inside temperature of the pipe, which can be assumed to be the same as the fluid temperature,
T2= the outside temperature of the pipe, which can be assumed to be the same as the air temperature outside the pipe,
L= the length of pipe over which the fluid will be transported,
r1= inner radius of the pipe,
r2=outer radius of the pipe,
ln=natural logarithm,
pi=3.14159,
Assuming an 84% efficient 400,000 btu/hr heater, the water will gain 336,000 btu per hour.
At 40 gpm, the water exiting the heater will be about 16.8 degrees Fahrenheit warmer than the water entering. Let's assume 70 degrees in and 86.8 degrees out.
At 80 gpm, the water exiting the heater will be about 8.4 degrees warmer than the water entering the heater. So, 70 degrees in and 78.4 degrees out.
Heat transfer depends on the difference between the exhaust temperature and the water temperature (among other things).
Natural gas burns at 3,542 degrees Fahrenheit. The exhaust temperature depends on the air flow rate.
The exhaust temperature exiting the heater is in the 300 to 350 range after 84% of the heat is transferred to the water, which means that the exhaust temperature is substantially higher when it makes contact with the heat exchanger.
Assuming that the exhaust temperature is about 1767 degrees Fahrenheit before it hits the heat exchanger, the temperature difference between the water and exhaust is so large that the slower flow will still gain more than 99.5% of the heat that the higher flow would get.
So, the temperature difference of 8.4 degrees will only have a very minor effect on the efficiency of the heat transfer.
In addition, once you exceed 40 gpm, a substantial amount of the flow begins to go through the internal bypass, which means that you probably wouldn't get more than 50 gpm going through the heat exchanger even if the flow going to the heater was 80 gpm.
The main thing to do is to keep the flow within the specifications as listed in the manual.
My recommendation is to stay close to the lower end as higher flow confers little to no benefit.
At 40 gpm, the water exiting the heater will be about 16.8 degrees Fahrenheit warmer than the water entering. Let's assume 70 degrees in and 86.8 degrees out.
At 80 gpm, the water exiting the heater will be about 8.4 degrees warmer than the water entering the heater. So, 70 degrees in and 78.4 degrees out.
Heat transfer depends on the difference between the exhaust temperature and the water temperature (among other things).
Natural gas burns at 3,542 degrees Fahrenheit. The exhaust temperature depends on the air flow rate.
The exhaust temperature exiting the heater is in the 300 to 350 range after 84% of the heat is transferred to the water, which means that the exhaust temperature is substantially higher when it makes contact with the heat exchanger.
Assuming that the exhaust temperature is about 1767 degrees Fahrenheit before it hits the heat exchanger, the temperature difference between the water and exhaust is so large that the slower flow will still gain more than 99.5% of the heat that the higher flow would get.
So, the temperature difference of 8.4 degrees will only have a very minor effect on the efficiency of the heat transfer.
In addition, once you exceed 40 gpm, a substantial amount of the flow begins to go through the internal bypass, which means that you probably wouldn't get more than 50 gpm going through the heat exchanger even if the flow going to the heater was 80 gpm.
The main thing to do is to keep the flow within the specifications as listed in the manual.
My recommendation is to stay close to the lower end as higher flow confers little to no benefit.
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I find my VSP likes around 2250 when running the heater. Keeps the bypass closed and the flow switch open
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