Friday, September 05, 2008 You Are Here: FAQ's  | 
 

Frequently Asked Questions (FAQ)
 
Q.  Does the HM Series have a maximum discharge air temperature? Is the high limit switch the only determining factor? The only thing I can find out is the temperature rise min/max table in the application guide.
Q.  I have a problem with a modulating HM unit. Do you have a step by step set-up procedure?
Q.  The indirect HM furnaces we buy from you, are they FM approved or rated?
Q.  What is the manifold pressure suppose to be on your HM duct heaters?
Q.  I have an application where I'm using two HMB400's stacked.  The airflow is 13200cfm and they require  +-5F discharge air control.  I know the lowest available temp rise is 5.6F at 8:1 turndown but do you feel the 8:1 should be adequate overall?  Any insight you can offer would be appreciated.
Q.  I found a part of the HMA intallation document that claims vertical outlet furnaces can be "B" vent. Can I actually do that or should I stick to "L" in case there is some pressure in the vent line?
Q.  Is there a restriction on using a side wall vent on an HE furnace?
Q.  When can I use aluminized steel heat exchangers and when do I need to specify stainless steel?
Q.  Why do the HM series modules have drain taps provided in the flue box?
Q.  I have a unit with a horizontal burner tray and the flue box is above the burners. Do I still connect a drain line to the flue box?
Q.  Does condensation occur in the heat exchanger during heating system operation?
Q.  What is a Category III appliance?
Q.  What is a Category I appliance?
Q.  Is a rain cap acceptable for the vent duct termination?
Q.  Do HM series furnace modules meet IRI requirements?
Q.  Why is the temperature rise limited to 60 oF in certain configurations?
Q.  Why is so important to arrange vent discharge to avoid flue gases from re-circulating into the combustion air supply?
Q.  Why is the size of the combustion air opening important?
Q.  Can I install the HM furnace modules on the suction side of the circulating air fan?
Q.  If I need a temperature rise higher than 90 oF, how can I achieve it with HM furnace modules?
Q.  I have constant volume airflow unit but the job specification calls for a 4:1 turndown capability. At 25% of maximum input the temperature rise would be 10 oF. Is this application OK?
Q.  What is the minimum gas supply pressure to HM units?
Q.  What is the maximum gas supply pressure to HM units?
Q.  I have a service regulator with 2 inch pipe inlet and outlet serving three 200,000 Btu heaters. I cannot get over 4.0 inches w.c. inlet pressure when all are turned on, but the chart for the regulator shows the capacity is two times the input of the heaters. Why?
Q.  Why do you have so many oreintations of your HM series module? Why do you need to know my airflow direction?
Q.  How do I wire an alarm contact into the HM (Duct Furnace) Fenwal's Ignition Control?
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