3120 HEWITT AVE 2018-01-02 MF Import

Mr. Jamie Johnson .Vay 6, 1976 Page Two when airflow across the burner drops below 50" of the rated CFI% This is more than adequate to supply the required combustion air to the unit and maintain a high rate of dilution of the products of combustion downstream. All air from the unit will be eventually exhausted to the outside in a safe manner because U the natural exfiltration resulting from pressure differential in the building. Without this exfiltration the static pressure buildup within the building would result in lose of airflow through the unit and initiate a shutdown due to the pressure differential switch. Our interpretation of Section 1904(e) allows an electrical interlock on the fan motor of the exhaust system to prevent the direct -fired unit from operating when the exhaust system is off. Item 3 In reviewing the definition of ''central heating plant'' in the Uniform Mechanical Cede -Section 405 and in the Uniform Building Code Section 404, it appears to include :Hake -up air heaters by lack of definition. It is my con- tention, however, that it was not the intent of these definitions and Section 1108 of. the U. B. C. or Section 704 of the U. M. C. to require one -hour enclosure of make-up air heaters, especially where there is already installed a separate 'central heating plant'' intended to heat the entire volume of the building for comfort reasons. 1' e woulu like to discuss the applicability of this section with the Department, if the Departme,it so agrees to allow a temporary and conditional approval pending outcome of our discussions. We are investigating [he safety and practical aspects of downrating the unit if code interpretations are not in support of our contention. if the agreed interpretation of the intent of the code does no: support our contention that the applicability of Section 1108, requiring a one -hour fire -rated occupancy separation, does not apply to direct -fired units then we will be nrepared to either 1) request a variance, 2) relocate the unit, or 3) de -rate the unit to lees than 400, 000 Btu per hour. We would like to clarify the intent of the code along this line, not be- cause of this single installation, but because of possible future installations that will be made under the revision in the 1976 code, which removes occu- pancy restrictions from direct -fired make-up air heaters. Your considera- tion of this request would be very much appreciated and would assist us in future planning and activities on such units. If you can and do agree to permit a temporary gas turn -on and operation of the unit pending our interpretative discussions, please advise me and 1 will