How To Move HVAC Ducts To Their Proper Wall Height Location

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    A friend of ours asks about their older single story ranch home without a basement that was retrofitted back in the 1970’s to change from Baseboard Hot Water from an Oil Heater to Forced Hot Air from a Gas Heater. In their case the install was done pretty poorly and they need to change the location of the register vents to increase the output and heating ability of the heater.

    Although in this case the proper sized furnace was installed the duct work for the heater was really poorly installed. In homes without a basement you have 2 choices. Either you go into the crawlspace which in this case is only about 14 inches high and the HVAC Techs couldn’t be bothered to do this or you go into the attic. Since it is easier, faster and would make the company more money they went into the attic with the duct work for both the feed and returns.

    The choice of the attic is not the worst thing in the world. In winter months the unheated area will lose a lot of heat off of the ducts and during the summer the hot air in the attic will effect the performance of the air conditioner however with proper insulation a system of this type can be effective. In our friends home the system can’t even keep up with heating the home because the return registers were installed directly in the ceiling and the feed registers were installed only about 16 inches down from the ceiling in all the rooms. When the system tries to heat the room the hot air comes into the room and flows across the ceiling and goes back into the return.

    In a normal system the feed registers are located at the lower part of the wall or in the floor and as hot air enters the room it flows into the entire room and eventually back through the return registers at the top of the wall. This is done because Hot Air rises and in the summer the cool air of the air conditioner can still work well because there is a large amount of flow and distance between the registers.

    In this case there are feed registers in the wall they just need to be moved down to floor height and then the system should work well. This is something that a homeowner can do themselves if they have basic tools and can do some drywall work.

    Changing The Location Of Your Heating Duct Registers

    Since the duct work is already in the wall all that needs to be done is to lower the height of the feed duct to floor height. To do this you will need to purchase some pre-made sheet metal duct work that is sized to fit in a wall void and then cut the old duct and extend it to the floor.

    Although most people don’t change their duct work the supplies are normally available at most larger home hardware stores. You can purchase in wall ducts, registers and even full sized duct that would be used to feed the main lines to each room.

    I don’t suggest that main feed lines be installed without some knowledge of HVAC design but if you need to replace a line and can get the same size you should be fine. The problem with feeding the main lines that go to each room is that they are sized in a way to increase flow at the most distant rooms and reduce flow at the registers that are closest to the heater. You will even find dampeners that restrict flow in these lines and they must stay in place for proper air flow.

    First you will cut back the drywall to expose the wall void. Then you will need to remove the 90degree turn or cut away a piece of duct so you can attach your extension. If you are careful you may be able to reuse this part at the new location. If the register is mounted by placing it over a simple hole in the duct then you will need to use a piece of sheet metal to cover the hole and then use screws to attach it.. then duct tape to seal it off.

    Install the new duct pieces in the wall void and then nail them with their flange to the studs in the wall. You want to make sure that the duct is tight in the wall or when it is heated and cools it will make a popping noise. If there are no flanges you will have to create them with some metal duct seam strips.

    Make sure that all the joints are tight then use sheet metal screws to attach the duck permanently. After it is attached you should use aluminum duct tape to seal all of the joints so that air isn’t lost from gaps.

    Cutting metal duct is not that difficult if you take your time. You will want to purchase some sheet metal tin snips and I suggest that if you don’t expect to be cutting a lot of metal that you get a straight cutter and don’t worry about the other tin snips that come in sets to cut in the left or right direction to make holes.

    Final Note

    Extending your duct work or moving it in a wall is not the hardest thing to do but you need to approach it in a professional manner. Your work should be tight and sealed off when completed. Remember to fasten your duct to the studs so that it is secure and the joints won’t pop when heated or cooled air is passing through it.

    In our friends case this is an unfortunate situation that never should have happened but probably did because the HVAC technicians that did the original install didn’t want to go through all of the trouble to open the entire wall and place the registers at floor height. This most likely resulted in extremely higher heating and cooling costs for the home owner. Then again this change over from oil to gas heating might have been completed by a home owner you never know.

    Feed Lines for HVAC or Air Conditioning must always be steel or an approved duct material that is fire resistant. Return lines can actually use just the wall void but this can be a dirty method and will result in more dust in your heating system and more servicing such as filter replacement.

     

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