It is very important that accurate airflow measurements be taken. The correct airflow is required in order for all components of the system not only operate at their best ( 15 SEER ) effiency, but also safely. Your system documents should give you the minimum required airflow for that system. Pressure readings should be taken to see what they are including the return air with the clean filter in place. Keep in mind, that as the filter gets dirty, the airflow will be reduced accordingly. Newly available high effiency filters must be sized properly, because they have a very large pressure drop even when clean. If the measurements show that the minumum required airflow cannot be attained, modifications to the duct system and/or return air filter system will be required. Please keep us posted, and feel free to contact us if you’d like us to review your service company’s results.

Ed

I have recently had an Electric Heater problem with a job that I had installed a year ago, and once I did the final check, test & start-up on the equipment and turned the equipment over to the building owner, that was the last I heard form them. I offered a maintenance agreement, but I was told the Tenant had their own HVAC company to do that…You’ve heard this story before!

I return to the building and find that the filters installed were the High Pleat type and only changed once in the 11 months since start-up, needless to say all three of the Heat-Pumps and Electric Heaters were down. Two of the heaters had to be replaced and in them I found your “User Caution” sticker. I read your Air flow bulletins, and was wondering if using the Heat Rise method over the electric heaters wouldn’t be an easier and more convenient way to check for sufficient air flow. While i carry a manometer in my service truck not all techs do. Would this method work for checking air flow across your heaters and if so what would be the Minimum ands Maximum temperature rise for the specific heaters?

Just my thoughts.

Glenn Roberts / Owner
Lawrence Service Group, Inc.

Your airflow with a clean filter should be at least 65 cubic feet per minute (CFM) per KW of electric heat, and 375 cfm per Ton of cooling. Airflow should be meassured accurately with the proper instruments and procedure. Unfortunately, many service technicians do not have the proper training or instruments, and often use unreliable methods and misleading data from the equipment manufacturers. Suggest you ask for a written procedure before having this done. We can look at it and offer suggestions, etc. If your compressor is noisy in the heat pump heating mode, or your electric heater is cycling on & off frequently, you probably have insufficient airflow.
Freezing of the indoor coil during the cooling mode is another indicator of low airflow.

In general, 4 & 5 inch thick filters will have lower clean filter pressure drops than the 1 inch type. However, you should still evaluate what minimum flow is required of the system you are referring to for proper operation of the electric heater and/or compressor, and what the degradation of the airflow is with the “clean” filter in place, keeping in mind that the flow will degrade further as the filter loads. Systems should never be allowed to operate below the minimum required airflow.
Ed