It’s that time of season again; for heating companies to advertise on how quick they can replace a furnace.
As with any business that sells a product, that product evolves over the years and decades. Forced air heating has gone from belt driven blowers, to direct drive blowers, to ECM blower motors, to two stage gas valves, and now modulating gas valves. But what is missed, by 90% of contractors, in this evolution - is that the Duct System has also evolved in its own way as-well. Duct Systems installed during the “belt driven blower” era are larger in square inches than what we would design today because the belt driven motor could not handle dealing with back pressure; thus the Duct System had to allow free air flow, with no resistance. Then the Direct Drive Blower was introduced and the square inches of the Duct System was reduced to create a static pressure within the Ducts. But at the beginning of the Direct Drive era, the duct systems were sized for heating only because most people could not afford central cooling. 4” & 5” pipe was used for the supply air runs which also reduced the size of the trunk lines. In addition, because the duct system was designed for heating only, the return air grills were placed low on the wall at the floor (also known as a base return) to remove the cool air off the floor during heating season; but 20 to 30 years later, A/C was added, and the duct system was never considered by the bidding contractor. The problem here is - the low-base return air grills: Cool air is heavier so it drops to the floor, and all that $$ used to cool the air going through the evaporator coil, returns back to the coil instead of remaining in the living area to cool it down. Basically the home owner is repeatedly paying to cool the cool air.
This is only one example of many more, why the Duct System must be involved when bidding to replace the equipment. Because of the evolution of Duct Systems and their design changes throughout this evolution; every furnace replacement my company has sold, duct changes/improvements were part of the bid which caused my company to be the highest bidder; but we got the job because we were the 'only ones' bidding to improve the duct system. All others only bided to change out the furnace in the quickest possible manner.
Half of these customers call me, some months later, and tell me their home has never been that comfortable throughout; and in fact, really didn’t believe it was possible.
What’s also important to mention here: if the comfort level of a home can be improved then what always follows without avail is efficiency is improved; the furnace uses less fuel. But this efficiency applies to the heating system as a whole (equipment, plenums, trunk lines, branches, register & grill layouts, and living area) and not the equipment’s efficiency. How it affects the equipment is it reduces the number of operating cycles in a given day. And how it accomplishes this - is another story in-itself, with an awful lot of science behind it. Bottom line, the furnace does not determine the comfort level, the Duct System Does!