All installations and services must be performed by qualified service personnel.

The preferred location of the outside combustion air intake termination (e.g. an optional stainless steel intake hood, part no.370183) is through the side of the structure, skirting or enclosure. An alternate termination location is under the structure in the skirted or crawlspace area providing a minimum of 50 square inches of free area exists around the perimeter for outside combustion air to be drawn through.

The furnace is shipped with a combustion air duct that must be installed in the bottom of the burner enclosure, before the burner is installed. This 2-inch by 7-inch duct is shipped in two pieces. High temperature silicone sealant should be applied to both vertical seams, before it is snapped together with four flanges on one end. The duct must then have high temperature silicone applied to the flanges. Then, the combustion air duct can be inserted through the opening in the floor base model no.70. When the combustion air duct has been inserted completely, secure the duct to the combustion adapter with self-tapping sheet metal screws, refer to Figure 6. Make certain that the flanges, duct, and adapter are completely sealed to the burner enclosure base with high temperature silicone caulk.

NOTE: The adapter may be cut with sheet metal shears to the appropriate size and secured over the inlet air duct opening. The adapter will convert the rectangular opening to a round connector ring. The ring will allow the connection of 2-inch I.D. flexible hose (provided) between the adapter and the inlet air boot, attached to the burner. Secure both ends of the flex hose with hose clamps (provided).

A 2-inch round to 7-inch x 4-inch rectangular, sheet metal, transition boot is supplied with the furnace for adapting a 4-inch round combustion air duct to the 2-inch x 7-inch combustion air duct. This boot has a screen inserted into the 4-inch round portion of the boot to provide a degree of protection from pests entering the furnace when the boot is terminated in the crawl space, or skirted area, directly below the furnace.

The material recommended for the combustion air duct is smooth, round, galvanized steel duct or schedule 20 PVC pipe. The maximum duct length allowed is equivalent to 40-feet of straight duct. Reduce this length by 6-feet for the intake hood and each 90-degree elbow used, and by 3- feet for each 45-degree elbow used the combustion air duct. Flexible, spiral, or corrugated duct is not recommended, due to the relatively high pressure drop associated with air movement through this type of passageway.

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Thermo Products GMC-85, OMC-70 service manual
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GMC-85, OMC-70 specifications

Thermo Products has built a reputation for delivering top-notch heating and cooling solutions, and the GMC-85 and OMC-70 models are no exception. These high-efficiency gas furnaces are designed to meet the diverse needs of homeowners while prioritizing energy savings and comfort.

The GMC-85 model is known for its impressive efficiency ratings, operating at an AFUE (Annual Fuel Utilization Efficiency) of up to 85%. This means that a significant portion of the fuel consumed is converted into usable heat, making it an economically sensible option for heating your home. Additionally, it features a multi-speed blower motor, which allows for better air circulation and consistent heating throughout the living space. This model also includes a durable heat exchanger crafted from high-quality materials, ensuring longevity and reliability in performance.

On the other hand, the OMC-70 furnace offers a slightly lower AFUE rating of 70%, but it shines in certain areas such as cost-effectiveness and straightforward installation. Its reputation for reliability is bolstered by its rugged design and construction that can withstand the rigors of various climates. The OMC-70 also includes a standard efficiency motor, contributing to reduced energy consumption while delivering appropriate heating requirements for smaller spaces.

Both models utilize advanced technology aimed at improving user convenience and efficiency. Features such as electronic ignition systems enhance reliability by eliminating the need for a pilot light, while also providing a quick and efficient startup process. Furthermore, each unit can be easily integrated with smart thermostats, allowing homeowners to manage their heating needs remotely for optimized performance.

Noise reduction is another characteristic that sets these models apart. Both the GMC-85 and OMC-70 employ sound-dampening technologies to ensure quieter operation, providing a peaceful environment for families.

In summary, Thermo Products' GMC-85 and OMC-70 furnaces present excellent options for homeowners looking to achieve comfort and energy efficiency. With their durable construction, advanced technology, and features geared toward enhancing user experience, these models provide reliable heating solutions suitable for various needs and budgets. Investing in either of these products translates to improved energy savings and consistent warmth, making them popular choices in today's competitive market.
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