What Is It?
The Lustron system is unlike most contemporary heating systems, such as forced air systems that distribute warm air into each room at specific point through wall or ceiling vents, or radiant heating systems that use electric coils or heated water pipes to radiate heat upward from the floor. It is a rather unique hybrid of both, utilizing warm air as a source of heat in a closed radiant system.
This unusual system is composed of three parts: a furnace suspended from support brackets in the ceiling of the utility room; the plenum located in the space between the ceiling and roof trusses; and a fan that moves the air from the furnace through the plenum. The original Lustron furnace was the “Williams Oil-O-Matic, Model 6050″ or the “Williams Gas-O-Matic.”
How Does It Work?The Lustron Corporation touted their design as the latest advance in clean and efficient heating technology. “The newest kind of heating for the newest kind of House. One of the original Lustron advertisements explains that “radiant heating-the latest development in modern heating engineering-operates on the same principle by which the sun’s rays warm the earth. Hot air from the overhead furnace unit circulates through a chamber built in the ceiling. As the temperature of the ceiling increases, the heat rays are radiated downward. Hot air does not circulate through the house. No uncomfortable air currents carrying dirt and soot are present.”
The original system relies on heated air that is continuously circulated with a centrifugal fan through a narrow plenum, which is a narrow ducting system located between the ceiling and the roof trusses. The air is heated by an oil- or gas-burning furnace that produces 75,000 Btu per hour. A fan moves the warmed air from the furnace into two supply ducts in the plenum, where it heats the porcelain-enamel metal ceiling panels, causing the heat from the forced air to “radiate” down from the ceiling into the house. In addition to filling the plenum and sub-chambers, some of the heated air is allowed to spill over into the exterior walls. This prevents condensation from forming on the metal walls or inside the wall structure.
The plenum system itself is composed of a number of components. (Cross section of duct installation taken from sheet EM-02-G-10.12 of the Erection Manual) Approximately 6 inches of loose insulation-fiberglass, mineral wool, or “insulwool”-is blown or hand-placed above the plenum chamber. The top of the plenum chamber is formed from 2-foot by 4-foot by 3/16-inch cement-asbestos (also called “transite”) boards. A sheet of aluminum foil (or “fire foil” as it is called in the Erection Manual) or corrugated asbestos is used to seal any gaps between the transite boards to reduce heat loss. The transite boards-composed of approximately 85 percent Portland cement and 15 percent asbestos fiber by weight-are clipped to the underside of the roof trusses with metal clips to form three sides of the plenum chamber, which is approximately 6 inches high. Finally, porcelain-enamel metal ceiling tiles are suspended from the roof trusses to create the bottom of the plenum chamber.
Within the plenum, each main supply duct leads to four sub-chambers formed by sheet-metal partitions. Two of the sub-chambers are located over the bedrooms, while the other two are over kitchen and living room. Within each sub-chamber is a maze of sheet-metal baffle plates. These plates direct the warmed air to circulate throughout the sub-chambers, creating an even distribution of heat. They also force cooled air to return to the furnace for reheating. Homeowners can control the flow of air into the sub-chambers with dampers, which are accessed by two sets of two small vertical rods descending from the ceiling in the utility room.
The furnace heats air to approximately 140 degree Fahrenheit, with the result that the average ceiling temperature during furnace operation is about 105 degrees Fahrenheit. As the heated air from the furnace moves through the plenum, its temperature typically decreases around 45 degrees Fahrenheit. This air is then returned to the furnace, where it is mixed with fresh air and reheated to 140 degrees. General temperature settings for the entire system are controlled by a conventional thermostat located in the living room.
Even if your furnace has been replaced as the heat source for the warm air circulating in the plenum, the principles of the heating system should still be the same, presuming no other changes have been made.
For more detailed information on the materials and installation of plenum, original Williams oil and gas furnaces, and electrical circuitry for the heating system, you may want to review the appropriate sections of the Erection Manual and Specifications:
- Plenum Panel Installation - EM-02-D-10.11 through EM-02-D-12.1
- Plenum Transite Installation - EM-02-F-10.1 through EM-02-F-10.12
- Installation of Insulation/Cross Section of Plenum - EM-02-F-20.11
- Duct Installation Details - EM-02-F-39.1 through EM-02-F-41.1
- Baffle and Duct Installation - EM-02-F-22.1, EM-02-F-23.1, EM-02-F-30.1
- Duct and Scuttle Installation Details - EM-02-G-10.12
- Installation of Furnace Hanger Brackets - EM-02-N-11.1 and EM-02-N-21.1
- Installation of Oil Furnace - EM-02-N-31.1 through EM-02-N-31.11
- Installation of Gas Furnace - EM-02-N-51.1
- Installation Chimney Flue - EM-02-N-90.1
- Installation Chimney Flue with Gas burner - EM-02-N-91.1
- Starting and Adjusting Instructions, Williams Gas-O-Matic Burner - EM-02-N-65.1 and EM-02-N-66.1
- Dial Settings of Furnace Controls - EM-02-N-68.1
- Heating Circuit - see Sheet EM-02-K-40.1
- Furnace Electrical Wiring Diagram - see Sheets EM-02-N-40.11 and EM-02-N-40.12
- Panel-Ceiling Installation - EM-02-G-10.1
- Panel Ceiling Installation Details - EM-02-G-10.11
- Ceiling Molding Installation - EM-02-G-21.1
Westchester Deluxe Architectural Plans Model 02 Home
- Radiant Heating System - AP2-J-100
- Master Specifications - 1949 Revisions
- Plenum - see Section I, pages 9-11 for information on installation and insulation requirements
- Furnace - see Section K, pages 13-15 for information on furnace, fan and control specifications
The Heating System: Common Problems and Repairs
Lustron houses were exceptionally well-insulated for their time, but they tend to fall short of today’s standards for comfort. Owners frequently complain that their houses seem cold and drafty, a condition that is further aggravated by the difference in temperature between the heated ceiling and the cold concrete floor slab. Some heating problems that are experienced by Lustron owners can be fairly minor and may only require simple solutions, such as adjusting baffles to better distribute heat or adjusting the set point on your furnace. Others can require a more complicated and costly solution, such as installing new or additional insulation in the attic and walls, repairing alterations made by a previous owner, or installing a new heating system. The section below will provide an overview of many of the common problems with the heating system and also suggest some solutions. As always, start with the simple solutions first and use a systematic approach.
Common Problems & Simple Solutions
Chilly? How About Your Thermostat?
The original thermostat was located on the living room wall. Do you have your original dial thermostat, or has it been replaced? Older thermostats may not register properly and could prevent your furnace from operating at the appropriate temperature, or at the appropriate time. The US Department of Energy Consumer’s Guide to Energy Efficency and Control Systems contains useful information on programming your thermostat.
You can contact a heating or mechanical professional to determine if your thermostat is reading the air temperature accurately and activating the furnace, or you check it yourself. A simple way to determine if your existing thermostat is accurate is by placing a digital temperature gauge next to it. Compare the two temperature readings. If they are more than a few degrees in difference, you might want to consider replacing the existing thermostat.
Installing a New Thermostat
If you choose to replace the existing thermostat, consider a “setback” or programmable model that reduces the temperature during off peak hours (at night, while you are at work or on vacation).
- For an overview of how to replace your existing thermostat with a setback thermostat, click here.
- The Energy Star website has a comprehensive section on programmable thermostats. Click here to take a look.
However, if you are using the ceiling radiant heating system, you may not want to set the temperature back more than ten degrees Fahrenheit since the energy required to reheat the panels from a low temperature could prevent you from realizing any cost savings. Experiment with the recovery time (the time it takes the furnace to get the room back up to temperature) to figure out the optimum setback.
Be aware that any new thermostat installation likely will require the drilling of new holes in your interior wall panels. To minimize damage to your panels be sure to drill as few holes as possible, make them as small as possible, and pre-drill any new holes with a drill bit designed for porcelain surfaces.
Still Chilly? Are Your Furnace Controls Set Properly?
This will depend upon the type of furnace that you have in your home. If you have an original Williams model, the proper setting information can be found in the Erection Manual, on Sheets EM-02-N-60.11 and EM-02-N-61.1 for the oil furnace, Sheets EM-02-N-65.1 and EM-02-N-66.1 for the gas furnace, and EM-02-N-68.1 for fan and limit controls. If you have newer furnace, you will need to reference the operation manual or specification for that model to determine the optimal settings. Erection Manual sheet EM-02-N-68.1 shows dial setting.
Be aware that the set point for new furnaces often are too low for the Lustron system. The original radiant heating system required the air from the furnace to be heated to 140 degrees Fahrenheit. Modern furnaces usually are set lower than this to maximize efficiency and reduce stress on the unit. These cooler set points do not provide enough heated air to warm all of the ceiling panels before the air cools and returns to the furnace. Contractors may advise against a higher set point to increase the life of the furnace, but a lower setting probably will not heat the ceiling panels adequately.
Unless you have some experience with mechanical equipment, it is advisable to contact a heating or mechanical professional to assess your furnace condition, determine if the controls are functioning properly, and adjust the settings.
Still Chilly? Check for Drafts
Make sure your windows are properly sealed and your doors have proper seals, for more detailed information visit the window section. To find out if you might have some gaps in your Lustron that are letting in air, during a windy day, utilize a candle or perhaps some incense and move it along the baseboard and around your windows (making sure your furnace is off to prevent drafts). If you have gaps, the flame smoke will be disturbed by moving air. Note where air is infiltrating. If air is coming in around the windows, utilize a clear silicone sealant around the perimeter of the window. Caulk any gaps between the wall and floor. You may also need to remove the baseboard that runs along the wall and meets the floor. Sometimes air can get in between the bottom of the wall panel and the floor. However, if you have a good rubber or vinyl baseboard, this should cut down dramatically on air infiltration. Make sure the bottom and door frames of your exterior doors have adequate weather stripping.
Clean Your Filter
Depending upon the type of furnace you have, you may need to clean the mechanisms or change the filters on a regular basis to ensure that it stays in optimal working condition. You will need to consult the manufactures’ information for your particular model to determine the appropriate intervals for cleaning and filter replacement, where the filters are located on your furnace, the proper procedures for cleaning, and, if necessary, where you can purchase replacement filters, if necessary. Although this is a fairly simple task, you can hire a mechanical or heating professional to assist you and explain the correct steps for cleaning your particular furnace unit, if you are concerned about performing these treatments by yourself.
Baffled by Your Baffles?
The baffles are thin metal sheets in the plenum that control the flow of heated air within the four sub-chambers in the plenum system. These sub-chambers are located over the rear and front bedrooms, the kitchen, and the living room. The setting of the baffles is controlled by a rather simple system of metal rods that position the baffles in each chamber. If this system is still in place, you will see two sets of two metal rods hanging from the ceiling in your utility room. Each rod controls a different baffle. If you stand facing the rear wall of your utility room, the two rods on your left will control the rear bedroom (far left) and front bedroom (near left). The two rods on your right will control the living room (near right) and kitchen (far right).
Erection Manual Sheet EM-02-N-21.1 (link to Erection Manual Sheet EM-02-N-21.1.) provides guidance on the correct setting for each rod. When they are in the full “down” position (pulled down completely), the baffles are closed. The two bedroom rods should be placed in the full “open” position (all the way up), while the living room rod should be in the “half closed” position, and the kitchen in the “two-thirds closed” position. (photo of hand adjusting baffle rods)
There is no alternative method to adjust the baffles to their recommended setting. If these rods are not visible, it is possible that they have been removed or have malfunctioned. If they have been removed, it would be necessary to dismantle the heating system to re-install them, contact a heating professional.
Owners who are not aware that the Lustron was designed with a radiant heat system have been known to cut holes in the ceiling panels in a misguided attempt to allow warm air to flow into the room, similar to a standard forced air system with vents. This type of alternation not only results in serious damage to the original porcelain enamel ceiling panels, but also to the heating system, which was designed to function as a closed radiant system.
Solutions to this problem require that the hole in the ceiling panel be repaired, either by removing the original panel and replacing it with a new panel; or by removing, repairing, and reinstalling the damaged panel. These treatments are discussed in detail in the section on Panels.(link to Panel Repair page) Note that previous alterations to the panels also may have damaged the plenum above. Before proceeding with any repair or replacement of the ceiling panels, consult a heating or mechanical professional to determine what impact this could have on the air flow within the plenum.
Install a New Furnace
If you have determined that you need a new furnace in your home, this may be a good time to reconsider your heating system in general. It might be useful to review the National Park Service Technical Preservation Bulletin No. 24: Heating, Ventilating and Cooling Historic Buildings, Problems and Recommended approaches.
Use this as an opportunity to fully explore your options, which include:
1. Utilizing the original radiant heating plenum and install a new ceiling-mounted furnace at utility room ceiling in the same location as the original. Consult with a heating or mechanical consultant to determine what type of unit might be best for your needs. Remember, the original Lustron furnace was designed to produce 75,000 Btus per hour and heat the air to a temperature of 140 degrees Fahrenheit. Your new furnace should meet these requirements to ensure proper heating of the ceiling panels.
2. Installing an electric radiant heating system over the existing concrete slab. More information on this option is provided below under Supplemental Heating.
3. Installing a high-velocity forced air system. These systems have been widely used for many years as a means to provide modern temperature and humidity controls in historic structures. It is a standard forced air system with vents, modified to operate at a high velocity. It uses small, flexible ducts in the walls and attic to distribute heated or cooled air to small round vent in the floor or ceiling. The blower unit for the system could be mounted in the attic or fat the ceiling of the utility room, much like the original furnace. The flexible ducts would run to the outside walls, just beyond the edge of the original plenum. By placing a condenser unit on the exterior of you house, you would have the benefit of adding air conditioning to the system. This is the only option discussed here that would accommodate air conditioning for your Lustron.
Note that a high-velocity forced air system would no longer require the plenum, and instead utilizes use small ducts outlets to circulate conditioned air directly into the rooms. This will require you to drill a register outlet and return air outlets in each room. The furnace contractor will size the unit as well as position the ducts in each room for maximum efficiency. You will want to work with the contractor to determine a location for the outlets that is the least visible but still accomplishes the task of heating and cooling. The high velocity systems have require a much smaller duct than normal forced air funaces.
To learn more about high-velocity forced air systems, you might want to explore these websites:
Install Supplemental Heating
If you’ve checked all of the options above and your Lustron is still too chilly for your comfort, then you are left with only one alternative-you must provide supplemental heat by installing an additional heating system.
Since the heat in the Lustron system radiates down from the ceiling, you may feel that the floor surface and the area near the floor is never warm enough. The only way to address this problem will be to provide a source of heat closer to the floor level, either in the form of radiant heat over the concrete slab of the foundation, or installing a baseboard heating system at the perimeter of each room. While neither of these options will be an easy or inexpensive job, you may want to consider the following issues to help you decide which approach might be best for your situation.
Electric floor radiant heating system - Unless you are planning foundation work that would require you to pour a new concrete slab, an electric system is preferable to a hydronic (water-based) system. The hydronic systems usually are a bulkier installation that will create noticeable differences in the floor level at your door thresholds, if placed over your existing floor slab. In addition, a hydronic system would require you to purchase and install a boiler in the already confined space of the utility room.
An electric floor radiant heating system will increase your comfort level in the home without requiring any significant changes to historic character or features of the Lustron. It can be installed over the original concrete slab and connected to your existing electrical box. You may need to upgrade your electric panel to handle the additional load. Contact with a qualified electrical contractor to make this determination.
There are several viable options for installation of a new radiant heating system over the existing concrete slab. These systems place a thin mat of electric coils over the existing floor, which are covered by a thin layer of “thin-set” mortar and whatever flooring materials you choose. The system will need to stop short of the interior doors to allow the thin-set mortar to be feathered to the level of the existing floor and door thresholds. This approach also affords you the opportunity to repair cracks and areas of separation at the juncture of the floor with the interior walls, reducing air infiltration and drafts.
If you would like to learn more about electric radiant heating systems, there are several manufacturers with information on their websites. A simple search for “radiant flooring” using your favorite search engine will help you identify manufactuers and insallers. There is also very helpful information on the US Department of Energy Website.
Baseboard heating system - Sorry! We do not recommend the installation of baseboard heat. The drilling required to mount the units and the updates to the existing electrical system would make it impractical because of the amount of damage that would need to be inflicted on the Lustron to install the system.