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The Furnace does not determine the Comfort Level, the Duct System Does!

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!


  • j a_2j a_2 Member Posts: 1,796
    I totally agree, about the duct sizing...that was some very good info you posted...there are just way to many people out here that that do not have a clue...meaning the installers...A customer has to rely on the contractor he choses, but most if not all think with there wallet not there head....Its funny the ones that will only do the job if it's done correctly are often called thiefs...I never once listened to my customers when they started telling me what I was going to install...And then they would say well the other guy said this and that...Then I would say well THATS YOUR GUY HAVE A NICE ...DAY...But heck if you don't file permits and don't carry insurance and use cheap help, and don't waste your time going to any type of training, and big box stores are your supply houses..and you don't pay licencing fees cause you don't have one anyway...and your help shows up in there pov, and open there there trunk to find there new shinny tools wife got him for his bithday from harbor freight...then puts his headphones on to listen to God knows what...dones his nice new work clothes so when he goes for his subs at lunch his buddy's think he's a plumber now...then goes to the bar and tells all his buddies how now he knows all about heating and plumbing stuff,and he can do it really really good and really really cheap
  • Jamie HallJamie Hall Member Posts: 12,387
    Install steam and be happy...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ProblemSolverProblemSolver Member Posts: 190
    The installers only do what they are told to do by what the salesman sells. The problem begins with the salesman. He's the one that should be educated along with the company owner; then the installers would be educated. Elementary!!!
  • ProblemSolverProblemSolver Member Posts: 190

    Install steam and be happy...

    you would say that. Lol
  • j a_2j a_2 Member Posts: 1,796
    Oh but then the customer posts a pic. Or two of his nice cheap install cause he has a few issues, but he can't seem to get hold of the installer Whoops.....Pipes bang, house cold, co going off, or furnace keeps going off on high heat because furnace oversized for duct work and it can't push all its air out..i know unplug the c o, crank up the pressure, and jump out those pain in the **** safety switches....The bandit in the beach wagon is in Florida enjoying your money
  • njtommynjtommy Member Posts: 1,105
    You maybe getting ear full for posting about furnaces/ duct work. You know these guys love steam and hydronics. lol.

    Not only the supply ducts, but it the return ductwork seem to be either undersized or just not enough of them.
    j a_2
  • Steve MinnichSteve Minnich Member Posts: 2,517
    In the 80's, I was a Journeyman tinner. But honestly, forced air bores me to tears. No offense.
    PHC News Columnist
    Minnich Hydronic Consulting & Design, LLC
    j a_2
  • ProblemSolverProblemSolver Member Posts: 190
    Steam is definitely more intriguing & hot water. Well... hot water can be boring if it's one zone and all baseboard. But I have learned and applied some things about forced air that requires a little more thinking & planning, and it works like a champ; and nobody out there knows about it or does it; at least I haven't met one yet. It's actually the reason I use ProblemSolver as my user name. Those areas in peoples homes that - no matter what they do - they can't get them to heat or cool very well. I go in and make it work with very little material; hence, I solve their problem.
  • ProblemSolverProblemSolver Member Posts: 190
    I'll share it with you guys, and title it "How Forced Air Works" as a new thread on The Wall. It's really simple actually, you just have to change how you think about forced air design.
  • HenryHenry Member Posts: 962
    I have found that the original duct work is usually lacking return air. When I first started to renovate the house, I made sure that the opennings in the floor or wall were full sized. I have an 11.5x15 washroom over the garage adjacent to my bedroom. The first year in the house it would not heat well nor cool. I installed at 6 inch return via one of the closets. It now has the same temperature as the rest of the rooms. I also keep the fan on. I have a full modulation York. I forgot what the low speed is, but it makes the house very comfortable as it keeps moving the air. Upstairs and downstairs have at most 1F difference.
  • ProblemSolverProblemSolver Member Posts: 190
    Your on the right track Henry. "The return air". Go to my other thread "How Forced Air Works". It's an ongoing explanation and a new way of looking at how it all works, or supposed to work.
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