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Best Pump RPM For Pool Heater

Best Pump RPM For Pool Heater
If you have a variable speed pump and a pool heater and you want to know what RPM you need to operate the heater the information on this page will help you. Unfortunately it is not going to be entirely straight forward. Swimming pool systems are surprisingly dynamic, and every swimming pool will be unique in terms of hydraulic design. In basic terms this means every pool is different and pump performance will vary greatly from one system to the next. So much so that it makes it impossible to give you a straight answer for what RPM you should set your pump to. So instead let's look at what information I can give you.


First, a long story about pool filtration systems, pipe size and flow rates can all be skipped more or less if you happen to have a flow meter installed on your system. Flow meters are the specific piece of equipment that you need, the missing link that most pool owners do not have that makes it difficult to know what RPM you should set your pump for...when single speed pumps dominated the pool filtration pump market flow meters were significantly less useful. Now, with the advent and even mandatory use laws of variable speed pumps, flow meters are a critical piece of equipment that really every swimming pool should have. Knowing what RPM you need to get your pool heater to run is just one of many, many reasons why a flow meter is a good idea if you own a pool. Here is an article with more information about why don't more pools have flow meters?


Assuming that you don't have a flow meter for your pool (yet) then this is where things get more complicated. The only unit of measurement that matters to your heater is the volume of water passing through it. Without a way to actually measure this volume of water means that you will have to do a little trial and error along with an educated guess in order to dial in on the correct pump RPM for your heater to operate.


Hayward Heater Minimum Flow Rates
H150 - 25 GPM
H200 - 25 GPM
H250 - 25 GPM
H300 - 25 GPM
H400 - 25 GPM


Pentair Heater Minimum Flow Rates
MT175 - 20 GPM
MT200 - 20 GPM
MT250 - 25 GPM
MT300 - 30 GPM
MT400 - 40 GPM


Jandy Heater Minimum Flow Rates
JXI200 - 30 GPM
JXI260 - 30 GPM
JXI400 - 30 GPM


You should reference your pool heater owners manual or manufacturer directly for accurate information about your heater make and model. What we can see clearly from this information published by major heater manufacturers is that minimum flow rates are not all that high. It warrants consideration that minimum flow rates are not necessarily optimal flow rates for pool heaters. Too low of flow rates for pool heaters can cause waffling (on and off) due to barely sufficient flow for operation. You may also experience incrementally more efficient water heating from higher flow values. Most heaters as you see have a minimum flow rate of 20 to 30 GPM, but they also have maximum flow rates ranging between 100 to 120 GPM. It is likely that operating at the bare minimum operating flow rate is at minimum less than ideal.



What pump speed do pool heaters need to run?
As you can see in the video on this page it does not take a high RPM to achieve the minimum flow rates for pool heaters to operate. 20 to 30 GPM is likely going to be less than 1000 RPM on many systems, of course understanding that every pool is unique. The number of suction and return pipes you have, the size of those pipes, the type and size of your pump and filter, as well as the distance from the pump to the pool and the elevation of the pump relative to the height of the water level in the pool...all of these are part of the equation for total dynamic head (TDH) which is the measurement of the resistance to flow within your plumbing system. You can measure momentary snapshots of a system TDH by measuring system pressure and system vacuum and applying multipliers to these values. Vacuum (in inches of mercury) multiplied by 1.13 added to pressure (in pounds per square inch) multiplied by 2.31 will give you the TDH in feet of head. TDH can be used to look up exact pump performance statistics using flow curves published by pump manufacturers. Or you can just get a flow meter. You should set your minimum pump RPM to be at least a few hundred RPM above the minimum value that makes your heater turn on. You can use a flow meter to set this value, or you can dial up the pump RPM until the heater starts and runs. Add a few hundred more RPM and this can be set as the minimum pump RPM for your heater to run.


Why did we add a few hundred RPM to the minimum pump RPM? The answer to this is that the flow rate of your pool system for a set RPM (or calculated value using TDH measurements) is only a momentary snapshot of the system conditions. Any change in valve settings or peripheral items will change the TDH values and flow rates. More commonly a concern the filter condition will change from clean to dirty over time. This has a direct and significant effect on system pressures, resistance to flow and ultimately the amount of water moving through your system for a given RPM value. Adding a few hundred RPM to your minimum pump RPM for heater operation helps to account for changing filter conditions. If you have a variable flow pump that has the ability to hold a specific flow rate under changing conditions you can just set your minimum flow rate values. If you have a variable speed pump the flow rates will change as the filter gets dirty so a few hundred RPM buffer is prudent to head off this potential issue.


Variable speed pump videos

Flow meters for swimming pools

Variable speed pump schedules

Variable speed pool pump reviews

How much power does a pool pump use?

Variable speed pump videos

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