Munchkin 399M manual Part 1. General Information, HOW IT Operates, Munchkin Ratings and Dimensions

GENERAL INFORMATION

PART 1. GENERAL INFORMATION

A. HOW IT OPERATES

When the room thermostat calls for heat, the Munchkin control board will start the circulator and start to monitor the return temperature of the system before the heater will begin to heat the water. Once the controller has sensed a drop in the return water temperature below the temperature set point minus the differential set point, the heater will start to heat the water. This eliminates the Munchkin starting every time the thermostat calls for heat. This feature keeps the system from short cycling.

Once the system has sensed the temperature difference, the Munchkin will activate the blower motor for 5 seconds to pre-purge the system before starting the Munchkin. The Munchkin controller will now start to modulate the pre-mix burner based on analyzing the return temperature, supply water temperature and the set point temperature. By compiling this information, the controller utilizes an algorithm to fully adjust the firing rate while maintaining the desired output temperature. The pre-mix burner fan has a direct drive current low-voltage motor with a pulse relay counting. This system allows precise control over the fan speed and combustion air volumes. Coupled with the Honeywell gas valve and the Venturi system which are set to provide a one-to-one ratio of precisely measured volumes of fuel to air, an accurate and instant burner output is achieved. This keeps the Munchkin running at the highest efficiency.

When the thermostat is satisfied, the Munchkin will then go through a 4 second post-purge cycle before shutting off. Every Munchkin heater is equipped with a display which will read the outlet temperature of the heater and then will illuminate a green light showing flame on. If a problem occurs, the front indicator light will turn red and the display will read a fault code; see Part 7, Section B/C, pages 33 and 34.

B. MUNCHKIN RATINGS AND DIMENSIONS

PERFORMANCE RATING

Model	Input Modulation	DOE Heating	Combustion Efficiency	Thermal Efficiency	AFUE*	Shipping Weight
399M	100,000 to 399,000	93,000 to 279,000	95%	93.35%	93%	252 lbs.

CONNECTION SIZES

	Supply/Return	Gas Connection
Model	Connection	Size	Vent Dia.
399M	2" NPT	1-1/4"	4"

RECOMMENDED SERVICE CLEARANCES

24"

FRONT

15"

24"

12"

(NOTE: The Munchkin is rated at zero clearance to combustibles.)

Figure 1-1 12"

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