www.pexuniverse.com PexUniverse - PEX, Plumbing, Heating, HVAC Supplies Industrial equipment supplier in Brooklyn, New York

Cast Iron Radiators

Available in multiple sections and sizes, these cast iron radiators are suitable both for hot water and steam heating applications in both residential and commercial settings.
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About Cast Iron Radiators

Due to their simple yet robust design, cast iron radiators have a long and proven track record in the domestic steam and hot water heating industry.
They are suitable for a very wide range of applications, from smaller residential to large commercial, and can work with virtually any type of hot water or steam boiler.

  • Inexpensive - when compared to other types of radiators on the market (aluminum, panel type, Victorian style and others).
  • Higher level of comfort - uses radiant heat instead or convection, resulting in more natural and proper temperature distribution.
  • Flexibility in installation - with a wide operating temperature range from 150°F to 220°F
  • High thermal mass - means less equipment (i.e. boiler) cycling & wear and higher energy efficiency.
  • It’s simple to install - no special parts are needed (such as diverter valves and thermostatic valve heads needed for panel style radiators).
  • Heavy - a single cast iron radiator may weigh anywhere from 40 to 150 pounds or more and will require a physically able person (or two) to position it in place.
  • Rough look - the radiator has a rough, unpolished surface which may be unappealing to some.


Radiator sizes available at PexUniverse include 4x19, 4x25 and 6x25 cast iron slenderized (tube style) models and 5x20 cast iron ray style radiators with different number of sections. For slenderized series, first number denotes the number of tubes and approximate depth of the radiator (4-1/2" for 4x19 & 4x25; 6-7/8" for 6x25 ), while the second indicates the height. For cast ray series, both numbers denote actual depth and height respectively.
4x19 and 4x25 models are best suited for residential and light commercial uses, whereas 6x25 models are mostly intended for larger commercial applications. 5x20 cast ray radiators are well suited for both uses.
Similarly to other types of radiators and baseboard heaters, cast iron radiators are sized based on BTU heat loss calculations.


The following features are standard on all cast tube/slenderized radiator models (4x19, 4x25 and 6x25):
  • (2) 1-1/4" FNPT bottom connections (with protective plastic caps)
  • (2) 1" FNPT top connections (with protective plastic caps)
  • Multiple 1/8" tappings (plugged) on the sides for air vent installation
  • Primer base coating, can be painted to match interior décor.
  • Legs for freestanding installation
The following features are standard on all cast ray radiator models (5x20):
  • (2) 1-1/4" FNPT bottom connections (with protective plastic caps)
  • Bottom grille (pipe & valve cover)
  • Multiple 1/8" tappings (plugged) on the front and sides for air vent installation
  • Primer base coating, can be painted to match interior décor.
  • Legs for freestanding installation

Recommended accessories

For hot water use:
1. Hot water radiator valves (Matco-Norca AHV series or similar).
2. Air vents (either manual - such as CK-100 model, or automatic - such as 417-3, HAV-125 models or similar, with 1/8" MNPT connection)
3. (2) black plugs to close the top 1" ports (4x19, 4x25 & 6x25 slenderized series only).
4. Brass or black bushings, if reducing the bottom connection to the radiator valve (or supply & return piping).
5. Y-strainer or dirt trap on the return line before the boiler (either standard or magnetic) - to collect and retain sediment.

For steam heating:
1. Steam radiator valves (Matco-Norca BARVY, BARVYN, SGV series or similar).
2. Air vents (such as Varivalve)
3. (2) 1" black plugs and (1) 1-1/4" black plug to close the unused ports (1-1/4" only for 5x20 cast ray).

Other parts may vary depending on the installation and can be found in the Heating Supplies category.

Frequently Asked Questions:

Q: What is the difference between cast tube and cast ray models?
A: Cast ray series (5" x 20") also utilize convection as a means for heat transfer, increasing the BTU output by over 50% comparing to a similar size cast tube models (4-1/2" x 19"). In addition, cast ray radiators are twice as heavy (section to section comparison) as cast tube.

Q: Can these radiators be recessed?
A: Only the 5x20 cast ray series are designed to be recessed (10-20% reduction in BTU output). Cast tube slenderized radiators are not designed for a recessed (in-wall) installation.

What is the recommended supply/return pipe sizes?
Pipe sizes are generally based on radiator surface area (sqft - see individual product specs for details) and the recommendations are as follows:
For hot water (2-pipe - 1 supply and 1 return): 1/2" for circuit (loop) 100 sqft and below, 3/4" for over 100 sqft.
For steam (1-pipe): 1" for up to 28 sqft, 1-1/4" for up to 62 sqft
Approximate surface areas are (per section): 1.6 sqft for 4x19, 2.0 sqft for 4x25, 3.0 sqft for 6x25 cast iron slenderized (cast tube) and 2.25 sqft for cast iron ray style.

Which of the air vent ports should be used?
It is best to use the top air vent port on the return side of the radiators for both hot water and 1-pipe steam applications.

Q: Can radiator covers be used with these?
A: Since radiators provide heat via radiant heating form of energy, any cover will create a barrier between the radiator and the room and will hinder it’s efficiency.

Q: The radiator rocks a little on one of the legs. Is this normal?
Yes, it is normal for the radiator to have a tiny wobble because it’s a large 1-piece rigid assembly. This will go away when radiator is positioned and connected to the piping.

What is the life expectancy of a cast iron radiator?
These radiators are expected to last a lifetime when properly installed.

Can they be painted?
Yes, they are coated with primer and can be painted with water-based paint to match the interior colors. Paint smell usually goes away within several hours after the initial start-up.

Do I need to install an air eliminator with these or will the air bleeders/vents work fine?
For hot water installation, air eliminators (also known as air separators) are highly recommended, since cast iron rusts easily in presence of oxygen and air eliminators help to capture and vent excess air molecules from the system water. We recommend using either Spirovent Jr or Taco 4900 series, or similar. In absence of an air eliminator, it is best to use rust inhibitor to protect the system.
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