Duct Water Heater | rickardair

Duct Water Heater

The Rickard Duct Water Heater is an energy efficient alternative to traditional neck electric heaters. When hot water (+/- 50°C) is available on site as a by-product of another process like cooling, that water can be used to heat the air supplied to a diffuser through this unit. Since the heated water is already available on-site, energy can be saved. The product is compatible with Rickard’s MLM controls provided the diffuser is fitted with a 24V Interface card to drive the 2-way 24V valve. Electric heat and Duct Water Heaters are best used for the spot heating of zones that aren’t being conditioned adequately by the central air-conditioning system, they are not generally used as the sole source of heating.

Rickard Duct Water Heater

The duct heaters have been designed to efficiently transfer the energy of the hot water. To achieve this, it was necessary to make a left and right-hand sided unit with an inlet shoe that faces up the duct into the direction of airflow. A left- or right-handed unit can be ordered or switched to either type on-site.

In order to securely hang the unit from the slab above, four M6 threaded hanger connection points are provided.

For an easy and leak free duct connection, the unit’s inlet has been designed with a 25mm flange. No gasket is supplied. All joints within the unit are sealed to prevent leaks.


A Duct Water Heater is designed to provide top-up heating to one or more VAV diffusers. They are designed to supplement the heating provided by the central air-conditioning system and heat outlier zones that are very cold when cooling is provided in summer. They are not intended as the sole source of heating.



When hot water (+/- 50°C) is available on site, typically as a by-product of another process like cooling, that water can be used to heat the air supplied to a diffuser through this unit. The product is compatible with Rickard’s MLM controls provided the diffuser is fitted with a 24V Interface card to drive the 2-way 24V valve. A 5m (max) cable connecting the diffuser interface board and valve is used. When additional heating is required the diffuser will call for heating, thereby opening the water heater valve. The valve is normally closed and therefore provides no heating without a signal. The duct heater valve starts opening when the room temperature is 0.5°C below setpoint.


The Duct Water Heater is designed to operate for 100 000 heating cycles. This is the equivalent of 20 years of use. A 2 year limited Warranty applies.


Rickard Air Diffusion (Pty) Ltd. warrants that its Duct Water Heater, including options or accessories shall be free from defects in material or workmanship for a period of two years from the date of shipment and agrees to repair or replace, at its option, any parts that fail during said period due to any such defects which would not have occurred had reasonable care been taken, provided that such parts have been inspected by Rickard and found defective and provided the diffusers have been given normal and proper usage and all parts and controls remain unaltered.

Rickard makes no warranty of merchantability of products or of their fitness for any other express or implied warranty which extends beyond the limited warranty above. Rickard’s liability for any and all losses and damages resulting from defects shall in no event exceed the cost of repair or replacement of parts found defective upon examination by Rickard. In no event shall Rickard be liable for incidental, indirect or consequential damages or damages or injury to persons or property. Rickard shall not be responsible for freight to or from its premises in connection with the inspection repair or replacement or parts under the terms of this limited warranty nor for the cost of removal or installation.

This warranty excludes any non-standard options or accessories installed in the field or factory.

Main Duct Inlet Connection Piece

The Duct Water Heater is made with a transition piece that is square or has a shoe. Both types are fitted with a flange for easy duct connection.


  • Shoe duct connection (standard). The shoe should point into the direction of airflow i.e. up the duct. The shoe is designed to reduce the pressure drop and to ensure the heater works at maximum efficiency. The Duct Water Heater comes as a left- or right-hand unit. The unit can be ordered as such or if need be adapted on site.
  • Square duct connection. Not recommended unless space is limited. Larger pressure drop and lower efficiency will occur when compared to shoe type.



  • Insulated - 3mm closed cell foam or 6mm closed cell Polyethylene foam (fire retardant, free of CFC’s and HCFC’s).
  • Uninsulated

Flexible Duct Outlet System

The Outlet is fitted with a cover plate to protect the outlet during transportation. The outlet can be cut to fit a spigot for a flexible connection or removed and replaced with a reducer manufactured by others.

Product Specs


  • Factory tested to 32 Bar
  • Assembly tested to 8 Bar

Rickards Duct Water Heater is fitted with a 24V Thermal Control Valve with the following Specs:

  • 16mm, 2-Way connection
  • Normally closed
  • Max operating pressure 0.25MPa/2.5Bar
  • Max holding pressure 1MPa/10 Bar



The Rickard Duct Heater has been designed to minimise the pressure drop across it. Please see the included performance data for design parameters and size selection. Water and air pressure drop, volume flow, inlet and outlet temperatures and corresponding heater capacities are tabled.

Please note that the current range of water heaters were sized for the following neck size diffusers. Should more than one diffuser be supplied from the same Duct Heater, the attached tables give guidance regarding the maximum number of diffusers that can be fitted. Please note, Rickard does not recommend that a pressure drop larger than 15Pa is exceeded between the take off and diffuser. These losses include the duct water heater, the flex +/-5Pa if less than 1.5m in length and any other fittings that might be added. Pressure drops larger than 15Pa will result in increased pressure at the diffuser at minimum which will result in over cooling and noise.

One Diffuser per Duct Water Heater Selection Table

One Diffuser per Duct Water Heater Selection Table





500x250 - 150 neck

500x250 - 200 neck

500x250 - 250 neck

500x250 - 300 neck

500x250 - 350 neck


700x300 - 150 neck

700x300 - 200 neck

700x300 - 250 neck

700x300 - 300 neck

700x300 - 350 neck