Condensate Pump Flow Rate: GPH and Head

What gallons per hour means on a listing

When a dehumidifier listing says the built-in pump moves a certain number of gallons per hour, that figure describes how much water the pump can push through the drain hose in one hour of continuous operation. It is a pump rating, not a measure of how much moisture the dehumidifier removes from the air. The dehumidifier's capacity, stated in pints per day, tells you how much water the unit can collect; the pump's GPH tells you how fast that collected water can be moved out.

The two figures are related but not the same. A dehumidifier rated at 50 pints per day can collect about 2 gallons per hour at its maximum removal rate, but the pump may be rated higher or lower than that. If the pump's GPH is lower than the rate at which the unit produces water, the pump could fall behind, and the unit may shut off on a full bucket or overflow. Read the GPH figure on the maker's page and compare it to the unit's stated capacity in gallons per day. For a guide to choosing a unit with the right pump, see the best dehumidifiers with pump.

• GPH is a pump output rating, not a moisture removal rating.
• Compare the pump's GPH to the unit's daily capacity in gallons.
• The listing title may not state GPH; check the maker's spec sheet.

What maximum lift head means

Maximum lift head, sometimes called shut-off head or max lift, is the highest vertical distance the pump can push water upward from the pump's location to the point where the hose discharges. It is stated in feet. If your drain is 10 feet above the dehumidifier, you need a pump with a maximum lift head greater than 10 feet, because the rating is the absolute limit, not a comfortable operating point.

The head rating assumes a straight vertical lift. Any horizontal run, bends, or narrow hose fittings add resistance and reduce the effective lift. A pump rated for 15 feet may only manage a 12-foot vertical lift if the hose has several elbows. Read the maker's manual for the recommended hose length and routing, and keep the discharge point below the maximum head.

For a basement dehumidifier draining to a floor drain, the lift is often zero because the drain is at the same level. For a unit in a basement draining to a sink or window above, the lift is the vertical distance from the pump to that outlet. Measure that distance before you choose a pump. For more on basement setups, see the best crawl space dehumidifier guide.

• Maximum lift head is the vertical distance the pump can push water.
• Measure from the pump's location to the discharge point.
• Bends and long hoses reduce the effective lift.

Matching pump output to your drainage needs

To match a pump to your drainage needs, you need two numbers: the dehumidifier's maximum water production in gallons per day, and the vertical lift from the pump to the drain. The pump's GPH should be at least as high as the unit's hourly production at its maximum capacity. For example, a 70-pint unit can produce about 8.75 gallons per day, so a pump rated at 1 GPH or more would keep up at peak output.

The lift requirement is separate. A pump with a high GPH but a low head rating will not work if your drain is high. A pump with a high head but a low GPH may not keep up with a high-capacity unit. Look for a listing that states both figures, and if only one is given, contact the maker for the other.

Some dehumidifiers with built-in pumps state the pump's GPH and head in the listing title or bullet points. Others leave it to the maker's spec sheet. When the listing is silent, the maker's page is the place to confirm the pump's ratings before you buy. For a list of models that include a pump, see the best dehumidifiers with pump guide.

When the pump rating matters most

The pump's flow rate and head matter most when the drain is above the unit. A basement with a floor drain at the same level does not need a pump at all; a gravity drain hose works. A basement with a laundry sink or a window well above the unit needs a pump that can lift the water that high. A crawl space with a drain outside and above the unit also needs a pump with sufficient head.

For a whole-house dehumidifier installed by a professional, the pump is often part of the installation, and the contractor sizes it to the lift. For a portable unit you place yourself, you are responsible for matching the pump to your setup. Read the maker's manual for the pump's rated GPH and head, and measure your actual lift before you rely on the pump.

If you are comparing two listings, one with a pump and one without, the pump's GPH and head are the details that tell you whether the pump version will work for your drain location. A unit with a pump rated for a 10-foot lift will not serve a 15-foot drain. The pump's ratings are part of the stated details you should compare. For a general overview of choosing a dehumidifier, start with the best dehumidifier guide.

What to read on the listing and maker's page

On a dehumidifier listing, look for the pump's GPH and maximum lift head in the bullet points or the spec table. The listing title usually names the pump as a feature but may not state the flow rate. The maker's page or the manual is where the exact figures appear. If the listing says 'pump included' but gives no GPH or head, that is a missing detail you should check with the maker.

The pump's GPH and head are separate from the dehumidifier's capacity in pints per day. Do not confuse the two. The capacity tells you how much water the unit can remove; the pump's GPH tells you how fast it can move that water out. Both matter for a setup where the drain is above the unit.

When you read the maker's page, note the conditions under which the GPH is stated. Pump ratings can vary with the lift and the hose diameter. The maker's manual will describe the recommended hose and the maximum lift. Follow that guidance for your installation. For more on hose connections, see the dehumidifier hose fittings and adapters article.

What this site cannot say about pump performance

This site does not measure pump flow rates or lift heights. The figures on a listing are the seller's stated details, and the maker's page is the source for the exact ratings. This article explains what the terms mean so you can read them on the listing and the maker's page, but it cannot tell you how a specific pump performs in your home.

For any question about installing a pump, routing a hose, or connecting to a drain, the maker's manual is the first place to look. If the manual does not answer your question, contact the maker directly. For a whole-house unit, a licensed professional should handle the installation. This article does not give installation advice. For more on pump lift height, see the dehumidifier pump lift height article.

What to pick for your situation

Questions

What does GPH stand for on a dehumidifier pump?

GPH stands for gallons per hour. It is the pump's rated output of water in one hour, not the dehumidifier's moisture removal rate.

What is maximum lift head on a dehumidifier pump?

Maximum lift head is the highest vertical distance the pump can push water upward, stated in feet. It is the limit, not a comfortable operating point.

Do I need a pump if my dehumidifier drains to a floor drain?

No. If the drain is at the same level as the unit, a gravity drain hose works. A pump is for lifting water to a drain above the unit.

How do I know if a pump's GPH is enough?

Compare the pump's GPH to the dehumidifier's maximum water production in gallons per day. The pump should be able to move at least that much water per hour at peak output.

Where do I find the pump's GPH and head ratings?

The listing title may not state them. Check the maker's spec sheet or manual for the exact GPH and maximum lift head figures.