AboutHoward Livingston Expertise Can answer questions on electrical control circuits, power supply,airflow & distribution, electrical components,refrigerant problems,gas, electric & propane furnaces.No boiler or refrigerator or oil fired furnaces experience.Just HVAC questions please.
Experience 35 years experience in residential & light commercial repair & installation.
Question I have a RUUD system in my house (Heat pump model # RPKA-031JAZ and air handler # RBHA-17J11NFDAI). My house is approx 1700 sq. ft. in size and was built in 1983. The problem that I have is that the ductwork in the attic is inadequate. Out of the 9 rooms that I have in my house, only two of them get cold or hot when needed to. I have shut off their vents and that has not helped. I have a large family room with vaulted ceilings and a dining room adjacent to it. There is only one vent in the ceiling. The box that is attached to the air handler output with all of the ducting hooked up to is 12 inches wide and 20 feet long and made of sheets of fiberglass glued together. I want to rip out the fiberglass box and rip out all of the old ducting and that is taped together and connected with several T's in it and replace it with Y connectors instead. The questions that I have are, "Are there requirements on the size of 'box' that I need to build that hooks to the air handler so that I can attach the ducts?" "What are the thumb rules associated with running ductwork, (i.e. size, length, connections)?" Thank you for your time.
Answer You have an "extended plenum" duct system now. They work if, after each drop to a room the size decreases to maintain pressure. If not, the last drop or 2 doesn't have any airflow.
A new plenum should be the same size as the outlet from the evaporator coil. Without an analysis of your house layout the best way is just use 8" flex duct to every room from the plenum. But if you use one run from the plenum to 2 rooms, start off with a 10" duct, the Y off to 2 8" ducts. A good rule is to divide the output cfm of the blower into the percentage sq. ft. of the rooms. So if one room is 50% of the total area, it gets 50% of the cfm. But a detaILED ANALYSIS is necessary to find the correct size duct for every room.But the 8" rule does well for the average. Got it ??
