Everything You Should Know About Total Dynamic Head

If you want to make sure all of your pool’s systems run as smoothly as possible, one thing you’ll want to look at is the total dynamic head (TDH). TDH can be a confusing topic – even for seasoned pool owners. So, if you want a better understanding of your pool, let’s dive into this guide that will cover everything you need to know about TDH.


Main Takeaways

  • Total dynamic head tells you how much resistance to the water flow there is in your pool’s hydraulic system.
  • Calculating the TDH ensures that your pool pump has enough horsepower to run the water through the pipes.
  • To calculate the TDH of a swimming pool, use this formula: (PSI x 2.31) + (Hg x 1.13) = TDH

What is Total Dynamic Head?

When you purchase a pool pump, the salesperson may ask you about your TDH or “feet of head.” But what is total dynamic head?

Total dynamic head is a resistance metric that calculates the pool hydraulic system’s resistance to the water flow, which is often calculated by “feet of head.” In other words, the TDH calculates how much back pressure you have in your plumbing, taking into account any friction losses in the plumbing system. 

Factors like the length of your pipes, the elevation, and the 45 and 90-degree turns in your plumbing all create friction loss in the water and, in turn, affect the TDH. Additional factors affecting the TDH include the pool filter, heater, backwash valve, return lines, water features, and other accessories.

Why is TDH Important?

Since the TDH affects the flow rate of the water going through your pool’s hydraulic system, it is an important piece of the puzzle that ensures you purchase the correct-sized pump for your pool. 

For example, if you purchase a pool pump that is much too small for the feet of head, your pump will have to work much harder to push water through the pipes.

The importance of TDH goes further than simply your pool pumps. Any pool accessories that utilize the pump will also be affected. For example, a roof-mounted solar heater requires water to flow through the system to the roof. This requires the pool pump to work as efficiently as possible – otherwise, your pool won’t heat as well as it should. By calculating the feet of head, you can take out all the guesswork and know immediately whether or not your pool pump has enough horsepower to handle pumping the water through your pipes to the roof.

On the flip side, if you purchase a pool pump with more horsepower than necessary, you can potentially cause damage to your filtration system by putting unneeded strain on it. Not to mention the monetary losses you’ll encounter from running a higher-power pool pump for no reason.

How To Calculate Total Dynamic Head

The average inground swimming pool will have a TDH of 50, and the average above ground swimming pool will have a TDH of around 30. But this measurement will differ according to the pipes, certain pool accessories, and other factors that can create additional resistance and affect how the water flows through your system.

To calculate the TDH of an existing swimming pool, read the PSI of the pressure gauge and the Hg of the vacuum gauge. Then, use this formula:

(PSI x 2.31) + (Hg x 1.13) = TDH

Once you have your TDH, you can use your preferred manufacturer’s performance chart to determine what size pump you may need for your pool.

Additional Head Loss

If you plan to add some pool accessories that will affect the feet of head, you’ll need to add the resistance you would get from the additions to your pool. 

For example, you’ll need to calculate the additional head loss you’ll encounter if you add a fountain or a roof-mounted solar heater.

To calculate this, add how many feet the water needs to travel upwards before gravity takes over. If your solar heater requires water to flow upwards for 10 feet until gravity can do its job, add another 10 feet of head to your TDH.

With all this said, you won’t need to worry too much about calculating your TDH unless you have a particularly friction-heavy plumbing system or pool accessories that create a lot of resistance. A rough estimate depending on whether you have an inground or above ground pool will work just as well in most cases, especially if you have a variable speed pump.

How To Choose The Right Size Pool Pump

Now that you have calculated the TDH of your pool, you’ll be one step closer to finding the right size pump for your pool. You’ll also need to calculate your minimum and maximum flow rate range. To calculate the flow rate, check out my pool pump size calculator.

Bottom Line

With your TDH calculated, you will better understand your pool and plumbing system. If you’re still unsure what size pool pump to use, contact a pool professional to look at your pool and advise. My top tip is to go with a variable speed pool pump. This will ensure that your pump will run at a low feet of head for regular water circulation. But it will also amp up and run at a high head if needed for additional accessories.

Have any more questions about TDH? Feel free to reach out. I am always happy to help!

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