Pool Heater Flow Rate vs Pressure Drop

What flow rate means on a heater listing

A pool heater listing may state a flow rate in gallons per minute (GPM) or in gallons per hour (GPH). The figure describes how much water can pass through the heater in a given time. On Pentair's pool heater product pages, Flow Rate (GPM) appears as a searchable filter attribute, which shows that the maker treats it as a stated detail worth comparing.

Flow rate matters because the heat exchanger can only release heat into the water that actually moves past it. The figure is part of the listing, not a promise about how much your pool will warm. The ENERGY STAR pool pump page makes the same point for pumps: filtration requires a lower flow than running a pressure cleaner, so flow figures always belong to a specific operation. A heater with a higher stated flow rate does not necessarily heat a larger pool; the flow figure describes the heater's design capacity.

When a title and bullet list give no flow figure, this site records that the detail is not stated by the seller, and the maker should be asked before purchase.

What pressure drop means

Pressure drop, also called head loss, is the resistance the plumbing applies to water as it moves through the circuit. Every component on the pad adds resistance, and the heater's heat exchanger is one of them. On a listing, pressure drop is stated in feet of head or pounds per square inch (psi).

Hayward's product pages offer a Total Dynamic Head Calculator, and that phrase is the term equipment makers use for the complete resistance of a plumbing circuit from the pump's suction to the return. The heater sits inside that total. A dedicated article on this site explains the term further: pool heater pressure drop.

How flow and pressure interact

Flow and pressure drop work against each other. The faster water is pushed through a heater, the more resistance the heat exchanger creates. A pump that moves a high flow on its own will deliver less flow once a heater sits in the circuit, because the heater adds head.

The balance between the two appears on the listing when the seller states both a flow range and a pressure drop. This site compares those stated figures but does not calculate whether your pump can deliver them. Matching the figures to a pump is a job for the maker's sizing page and for the installer.

Related listing terms on this site include pool heater flow rate range and maximum flow rate.

• stated flow rate in GPM or GPH
• stated pressure drop in feet of head or psi
• the pool type the listing names, above ground or inground
• the heater type, gas, heat pump, or solar

Why this site matches no flow rate to a pool

Sizing a heater to a pool needs turnover time, plumbing length, and the pump's curve, none of which a listing states. This site explains the terms and compares stated details only; it matches no flow rate to a pool size.

For the actual match, use the maker's sizing page, usually linked from the product description or the manual, and ask an installer how the heater's flow requirement fits the pad. The same applies to pressure drop: the installer sees the whole circuit, the listing does not.

The heater type shapes both figures. Gas heaters, heat pumps and solar heaters list different flow behavior, and the type guides on this site reflect that.

Reading flow and pressure words on two listings

The table below is for reading listings, not for matching. When two heaters state the same flow range, the pressure drop figure tells you which one adds less resistance; the maker and the installer decide what your pump can push.

Questions for the maker and the installer

Keep the questions tied to the listing. If a title states both a flow figure and a pressure drop, the maker can usually confirm the operating range. If a title states neither, the seller's phrase not stated is a reason to read the manual before choosing. Compare heaters across the above ground and inground guides on this site, then take the shortlist to an installer.

• What flow range does the heater accept for your pool type?
• What pressure drop does the heater add at the flow your pump can deliver?
• Does the heater have a flow switch, and where is it described in the manual?
• Where is the maker's sizing page published?
• Which components of the pad must the installer confirm before start-up?

What to pick for your situation

Questions

What does flow rate mean on a pool heater listing?

Flow rate, stated in gallons per minute (GPM), is how much water can pass through the heater in a given time. Pentair's heater product pages list Flow Rate (GPM) as a filter attribute. It is a stated detail, not a heating promise.

What does pressure drop mean?

Pressure drop is the resistance the heater's heat exchanger adds to the plumbing circuit, measured in feet of head or psi. Hayward's pages offer a Total Dynamic Head Calculator, and the term is explained in the pressure drop article.

How do flow rate and pressure drop interact?

Higher flow means more water through the heater, but the heat exchanger creates more resistance at higher flow. The pump has to overcome the heater's pressure drop, so the two figures belong to the same balance.

Why does this site not match a flow rate to your pool size?

Matching requires turnover, plumbing length, and the pump curve, none of which a listing states. This site compares stated details and points you to the maker's sizing page and an installer.

What should you compare on two heater listings?

Compare the stated flow rate in GPM, the stated pressure drop in feet of head or psi, the pool type the listing names, and the heater type. If a figure is missing, the listing says not stated by the seller and the maker should answer.