Pump Sizing for Circulation, Table B | A.O. Smith 705 Series 100

Pump Sizing for Circulation

1.Use the chart below or one appropriate for your conditions to determine the heat loss in the length of the hot water supply and return piping. For example, 100 ft of 1-1/2 in bare copper tubing results in a heat loss of 5300 Btu/h.

Approximate Heat Loss from Piping at 140 ºF Inlet, 70 ºF Ambient *

Nominal Size, in.	Bare Copper Tubing,	1/2 in. Glass Fiber Insulated
	Btu/h-ft	Copper Tubing, Btu/h-ft

3/4	30	17.7

1	38	20.3

1-1/4	45	23.4

1-1/2	53	25.4

2	66	29.6

2-1/2	80	33.8

3	94	39.5

4	120	48.4

* Source: 2003 ASHRAE Handbook HVAC Applications

Table “B”

2.Determine the acceptable temperature drop at the last fixture in the loop. For example, if the supply temperature from the water heater is 120 ºF (49 ºC) and an acceptable temperature at the last fixture is 100 ºF (38 ºC) then the acceptable temperature drop is 20 ºF (7 ºC).

3.Calculate the required pump flow rate using the following formula:

FLOW RATE (gpm) =	HEAT LOSS (BTU / h)
	500 X ACCEPTABLE TEMPERATURE DROP (ºF )

4. Based on the above calculations select a pump for the type of circulation system you will be utilizing:

A). Preferred Method (reference drawing H-1-RP) - Reference pump manufacturers flow vs. pressure specifications to select a pump that can provide the flow rate calculated above while overcoming the pressure loss through:

•Tank water heater (reference manufacturer’s information)

•All building supply and return plumbing in the circulation loop (reference local plumbling codes, standards, or practices)

B). Optional Method (H-1-RO) - Reference pump manuf acturers flow vs. pressure specifications to select a pump that can provide 3 gpm of flow or the flow rate calculated above, whichever is greater, while overcoming the pressure loss through:

•On demand water heater (reference flow vs. pressure curve of the model being used)

•Optional storage tank (reference manufacturer’s information)

•All building supply and return plumbing in the circulation loop (reference local plumbling codes, standards, or practices)

NOTE: Only use pumps of brass or stainless steel construction. Do not use pumps of iron construction as they will oxidize and clog the inlet filter on the appliance.

705 Series 100, 186965-001, 505 Series 100, 305 Series 100 specifications

A.O. Smith is a leading manufacturer of water heaters and has long been recognized for its commitment to innovation and quality. Among their diverse product lineup, the 305 Series 100, 505 Series 100, 186965-001, and 705 Series 100 models stand out as reliable solutions for both residential and commercial water heating needs.

The A.O. Smith 305 Series 100 is known for its impressive energy efficiency. Utilizing advanced insulation technologies, this model minimizes heat loss, ensuring that water remains heated for longer periods. It features a durable tank construction, often built with glass-coated technology that prevents corrosion and extends the lifespan of the unit. This series also comes equipped with a user-friendly digital thermostat, allowing homeowners to set the desired temperature easily.

On the other hand, the 505 Series 100 emphasizes capacity and performance. Designed to supply hot water for larger households or commercial settings, this model boasts a high recovery rate, which means it can heat water quickly even during peak usage times. Its robust heating element and energy-efficient design ensure significant savings on energy bills, making it a smart investment. This series also includes safety features, such as a thermal relief valve, protecting against overheating.

The A.O. Smith 186965-001 model is particularly notable for its compact design. Ideal for installations with limited space, it does not compromise on performance. This model often includes smart technology, enabling remote monitoring and control via mobile apps. This feature allows users to track water usage, receive maintenance alerts, and manage settings from anywhere, enhancing convenience and ensuring the unit operates at optimal levels.

Lastly, the 705 Series 100 exemplifies versatility and high efficiency. With options for both gas and electric heating, it accommodates a wide range of consumer needs. It incorporates advanced safety elements, such as flame arrestors and high-temperature limit switches, which prioritize user safety. Additionally, the 705 Series is designed for easy installation and maintenance, enabling homeowners to enjoy peace of mind.

In summary, the A.O. Smith 305, 505, 186965-001, and 705 Series 100 all exemplify the brand's dedication to engineering excellence. With their unique features, cutting-edge technologies, and design characteristics, these models cater to various heating needs, delivering reliable hot water solutions for homes and businesses alike.