Imperial Gallons per Minute (imp-gal/min) to Cubic feet per hour (ft³/h) conversion

What is the Imperial Gallon per Minute?

The imperial gallon per minute is a unit of volumetric flow rate, measuring how many imperial (UK) gallons of liquid pass a point each minute. It is common in British and Commonwealth plumbing, pumping, and irrigation specifications.

Definition

One imperial gallon per minute equals one imperial gallon (4.54609 litres exactly) of volume flowing every 60 seconds:

$$1\ \text{imp-gal/min} = 0.0757682\ \text{l/s}$$

Because the imperial gallon is defined as exactly 4.54609 L, the exact relation is $4.54609 \div 60 = 0.0757681\overline{6}$ L/s. Note that the imperial gallon is about 20% larger than the US liquid gallon (3.785411784 L), so an imperial gpm is a larger flow than a US gpm.

Origin and History

The imperial gallon dates to the British Weights and Measures Act of 1824, which fixed it as the volume of 10 pounds of distilled water. It was redefined in 1976 (effective 1985) as exactly 4.54609 litres. The "per minute" flow rate arose naturally from waterworks and pump ratings, where minutes are a convenient interval for reading meters and sizing equipment.

Law and Notable Facts

The imperial gallon remains a legal unit in the United Kingdom and several Commonwealth nations, though the litre per second and cubic metre per hour are the SI-based standards for engineering. A tap flowing at 1 imp-gal/min delivers about 4.55 litres every minute; UK water-efficiency guidance often rates fittings in litres per minute, where 1 imp-gal/min corresponds to roughly 4.55 L/min.

Real-World Examples and Conversions

• A typical domestic kitchen tap or shower flows around 2 to 3 imp-gal/min (about 9 to 14 L/min).
• 1 imp-gal/min equals 60 imperial gallons per hour, or approximately 4.546 cubic metres per hour when multiplied out over an hour ($0.0757682 \text{ l/s} \times 3600 = 272.77$ litres/hour, i.e. 0.27277 m³/h).
• To convert to US gallons per minute, multiply by 1.20095: 1 imp-gal/min ≈ 1.201 US gpm.
• A small garden pump rated at 10 imp-gal/min moves about 0.758 litres per second, enough to fill a 200-litre water butt in roughly 4.4 minutes.

What is Cubic feet per hour?

Cubic feet per hour (CFH) is a unit used to measure the volumetric flow rate. It represents the volume of a substance (gas or liquid) that passes through a specific area per hour, measured in cubic feet. It's a common unit in various fields, especially when dealing with gas and air flow.

Definition of Cubic Feet per Hour

Cubic feet per hour (CFH) is defined as the volume of a substance, measured in cubic feet, that flows past a point in one hour.

$$1 \text{ CFH} = 1 \frac{\text{ft}^3}{\text{hour}}$$

How CFH is Formed

CFH is derived from the basic units of volume (cubic feet) and time (hour). It directly expresses how many cubic feet of a substance move within one hour. No special law or constant is specifically tied to the definition of CFH itself. It is a direct measure of flow rate, useful in practical applications.

Calculating Volume Flow Rate

The volume flow rate (Q) in cubic feet per hour can be determined using the following formula:

$$Q = A \cdot v$$

Where:

• $Q$ = Volume flow rate (ft³/hour)
• $A$ = Cross-sectional area of the flow (ft²)
• $v$ = Average velocity of the flow (ft/hour)

Another way to calculate it is:

$$Q = \frac{V}{t}$$

Where:

• $Q$ = Volume flow rate (ft³/hour)
• $V$ = Volume (ft³)
• $t$ = Time (hours)

Real-World Examples of CFH

• Natural Gas Consumption: Home appliances like furnaces, water heaters, and stoves are rated in terms of CFH to indicate their natural gas consumption. A typical furnace might consume 80-120 CFH of natural gas.
• HVAC Systems: Air conditioning and ventilation systems use CFH to measure the airflow rate in ductwork. A residential HVAC system might require airflow rates between 400 and 1600 CFH, depending on the size of the home.
• Compressed Air Systems: Pneumatic tools and equipment in factories use compressed air. The compressor output is often rated in CFH or cubic feet per minute (CFM, which can easily be converted to CFH by multiplying by 60) to indicate the volume of air it can supply.
• Industrial Processes: Many industrial processes, such as chemical manufacturing or food processing, involve controlling the flow rate of liquids or gases. CFH can be used to specify the desired flow rate of a particular fluid. For example, a chemical reactor might require a flow of 50 CFH of nitrogen gas.
• Ventilation Systems: Exhaust fans in bathrooms or kitchens are often rated in CFM (cubic feet per minute), which can be converted to CFH. A typical bathroom exhaust fan might be rated at 50-100 CFM, which equals 3000-6000 CFH.