What are the Self-Priming Hot Tub Pump Options?

Self Priming Pump Hot Tub

Self-Priming Hot Tub Pump? If you are not able to build your control room for your DIY hot tub below ground, then you are going to need a Self-Priming Hot Tub Pump. But what are the options? In this blog post, I will discuss the two main options that you have for self priming pump setups on your DIY hot tub build.

What is a self-priming hot tub pump?


A self-priming hot tub pump is a type of centrifugal pump that is capable of automatically removing air or gases from the suction line and creating a vacuum to draw in and pump liquids. Unlike standard centrifugal pumps which are found on hot tubs, which require the pump casing to be filled with liquid before operation, self-priming pumps can start pumping without the need for manual priming.


The self-priming capability of these pumps is achieved through the use of a specialized design and additional components. They typically have a built-in reservoir or chamber that holds liquid, allowing the pump to maintain a prime even when the suction line is empty or contains air. The pump creates a partial vacuum in the suction line, drawing in liquid from the reservoir and effectively priming itself.


Self-priming pumps are commonly used in applications where there is a possibility of air entrainment, intermittent flow, or situations where priming the pump manually may be difficult or time-consuming. They are widely employed in various industries such as agriculture, construction, wastewater management, and firefighting, among others.


It’s important to note that while self-priming pumps offer convenience and operational advantages, they may have limitations in terms of suction lift height and the viscosity of the pumped liquid. The manufacturer’s instructions and specifications should be followed to ensure proper operation and maintenance of the pump.


Why are large single speed self priming pumps hard to come by?


Large single-speed self-priming pumps can be challenging to find nowadays due to several factors:

  1. Advancements in Variable Speed Drive (VSD) Technology: Variable speed drives have become increasingly popular in the pumping industry. They offer better control and energy efficiency by adjusting the pump speed based on demand. Variable speed pumps can often achieve the same functionality as large single-speed pumps while providing additional benefits such as optimized energy consumption, reduced wear and tear, and improved system performance. Consequently, manufacturers have focused more on developing and promoting variable speed pump solutions.


  1. Market Demand and Trends: The market demand for large single-speed self-priming pumps has decreased as variable speed drives have gained prominence. Industries and applications that previously utilized large self-priming pumps have transitioned to more flexible and energy-efficient variable speed pump systems. As a result, manufacturers have shifted their production focus to cater to the changing market demands.



  1. Technological Limitations: Designing and manufacturing large self-priming pumps presents certain challenges. These pumps require specific engineering considerations to ensure reliable and efficient operation, particularly when dealing with large flow rates and high suction lift requirements. As the size of the pump increases, the engineering complexities also escalate, making it more challenging to maintain optimal performance and self-priming capabilities.


  1. Specialized Applications: Large self-priming pumps are often required for specific applications or industries with unique needs. These pumps may not be as commonly used as their smaller counterparts. As a result, manufacturers may prioritize more commonly used pump types and sizes, leading to limited availability of large single-speed self-priming pumps in the market.


Why is this a problem for us DIY Hot Tub builders?


This is a problem for us DIY hot tub builders where the amount of flow is important to our projects. If we are building a hot tub with 16 jets, we need 160 GPM of flow. If we can only get small variable speed self priming pumps, then this means we are not going to have enough flow.


Previously, we used to be able to get hold of large single speed self primers however, as I have indicated above, these are becoming few and far between as manufacturers discontinue their ranges in lieu of smaller variable speed models.


What are the options for Self-Priming Hot Tub Pumps?


The first option is that you opt for a smaller pump and you run less jets with it. So, instead of trying to run a 16 jet system on a single pump, you split this into 2 x 8 jets. That way, you only need to find a self priming pump that can output 80 GPM which is much easier to find and run two of them in your setup.


The second option is to run a self priming loop on a centrifugal hot tub pump.


What is a self-priming loop?


I have a full article here on this


Below is a diagram that shows a self-priming loop. In this explanation, I am going to refer to the color-coded pumps and gate valves in the diagram 

Priming Circuit Hot Tub Pump

On initial setup, to prime the system, the pink and turquoise ball valves would be closed and the yellow ball valve open.

This then placed the self-priming pump and the centrifugal pump in series. The self-priming circulation pump is forcing water through the centrifugal pump and back to the tub through the pipework.


I left it running for a couple of minutes, then shut off the system.


As it is pressurised, the water does not flow back into the tub and the pump stays primed.

The yellow ball valve was closed, turquoise ball valve open and pink ball valve opened too. This now puts the pumps in parallel where the flow rate can now be increased. As the system is pressurised, the system remains primed.


Now, the 5HP centrifugal jet pump can operate. Bingo!


Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi


Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi

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