Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

# Domestic Hot Water Heaters - Sizing

## Domestic Hot-Water sizing equations - heating capacity, recovery rate and power supply.

Domestic hot-water systems supplies taps in houses or buildings with hot water.

### Output Heating Capacity

Output heating capacity of a domestic hot-water system:

hout = q ρ dt cp                                (1)

where

hout = heating capacity, output (Btu/h)

q = flow rate (gph)

ρ = 8.34 - density of water (lbs/gal)

dt = temperature rise (oF)

cp = 1.0 - specific heat of water (Btu/lboF)

### Input Heating Capacity

Input heating capacity of a domestic hot-water system:

hin = q ρ dt cp / μ                             (2)

where

hin = heating capacity, input (Btu/h)

μ = efficiency

### Recovery Rate

Recovery rate for an electrical heater in a domestic hot water system:

RR = hin μ / dtρ

= P (3413 Btu/kW) / dtρ                              (3)

where

RR = recovery rate (gal/h)

P = electrical power supplied by heater (kW)

### Temperature Rise

Temperature rise in an electrical heater in a domestic hot-water system:

dt = hinμ / qρ

= P (3413 Btu/kW) / qρ                                (4)

### Electrical Power Supply

Electrical power supply to a domestic hot-water systems:

P = q ρ dt cp / (3413 Btu/kW)                                (5)

## Related Topics

• ### Water Systems

Design of hot and cold water service and utility systems with properties, capacities, sizing of pipe lines and more.

## Related Documents

• ### Domestic Service Water Supply Systems

Introduction to general design of domestic service water supply systems - with pressurized or gravity tanks.
• ### Fixtures - Hot Water Content

Content of hot water in some common used fixtures - basins, sinks and baths.
• ### Hot Water Circulation System - Return Pipes

Hot water can be circulated through a return pipe if it's instantly required at the fixtures.
• ### Hot Water Consumption vs. Occupants

Consumption of hot water per person or occupant.
• ### Hot Water Storage Tanks - Capacities vs. Dimensions

Dimensions and capacities of hot-water storage tanks.
• ### Hot Water Supply - Flow Rates to Fixtures

Hot water consumption of some common equipment as basins, sinks, baths and showers.
• ### Water - Human Activity and Consumption

Activity and average water consumption
• ### Water Supply Systems - Online Design Application

Free online tool for designing water supply systems in buildings.

## Search

Search is the most efficient way to navigate the Engineering ToolBox.

## Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

About the Engineering ToolBox!

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .

## Citation

• The Engineering ToolBox (2005). Domestic Hot Water Heaters - Sizing. [online] Available at: https://www.engineeringtoolbox.com/hot-water-d_956.html [Accessed Day Month Year].

Modify the access date according your visit.

7.8.15

.