I recently installed a cold air return in my home for my furnace. I did this because I have a wood stove insert in my basement and I was hoping to circulate that warm air throughout my home. Once completed, this worked out very well. The new air return, which is just above the wood stove, pulls the warm air from that room in, cycles it through the furnace and distributes it through the rest of the home via the registers in every room. Since the air being pulled in is already so much warmer and it is distributed through the rest of the house, the furnace actually runs less to produce heat. Here is how I did the installation.
First, I did some research on this. I had heard of others doing this but I had no experience in working with a central forced air system. I did the research just by searching on Google for installing cold air returns. I was fairly disappointed with what I found. I never really found anything that said to follow these steps. This could be because there are some fairly complicated issues regarding negative or positive pressure. That meant very little to me so I read on.
The idea behind a forced air system is that the same amount of air that is being pushed into a room from the registers is also being pulled from the room via the return vents. This keeps a nice even pressure in the room. If you are pushing more air in than you are taking out, you may create a positive pressure. Likewise, if you pull more air out than you push in, you can create a negative pressure. The exception to the idea of keeping it even is with bathrooms and kitchens. Since these rooms frequently have odors associated with them, you don’t normally want to put a return into these rooms. If you did, the odors could be pulled into the system and distributed through the rest of the house. Ewwww.
Now, even with this simple idea of keeping the pressure even, it isn’t quite so black and white in a real application. Since the major rooms in a house are open and not sealed from the other rooms, the air moves around anyway. So you could be pushing extra air into your living room and pulling extra air from your dining room. Since those rooms are all open, ultimately the pressure evens out, hopefully. If you have several levels to your home, air will also move between the upstairs and the downstairs.
So now I was armed with this important information, but what did it mean? How would I know if I created an uneven pressure by installing the additional air return? If I did create an uneven air pressure, what would that mean? Would the house implode? Ultimately, knowing this information meant very little to me in the actual application of the return. I decided that, without paying for an expert, I wasn’t going to have any idea if I would create an uneven air pressure before or after the installation of the cold air return. My approach was to allow for the ability to close off the new return in case something went terribly wrong after installing it. I did this simply by purchasing a close-able grille for the new return. I also purchased another close-able grille for some of my existing returns that were in key areas around my home. This would allow me to adjust the amount of air being pulled throughout different areas of the house, in case there was a problem. In addition, this also has allowed me to increase the draw from the new return by closing off more of the other returns. This was my best idea of protecting me from uneven pressure and it seems to be working fine.
So, with the threat of uneven pressure solved, it was time to plan out the specific location of the return. Two factors came into play here. The first was where could I place the return that would get the most heat from that room. The second was what potential locations are easily accessible for a do-it-yourself-er like me. Fortunately, my basement has a drop ceiling which makes work such as this easy. I chose a location just in front of the fireplace where most of the heat, coming directly from the fireplace, is located. Since it was a drop ceiling, it was also easy to get to.
Now knowing where I wanted the return to be, I had to locate the main return duct that would allow me the space to cut into it. I found the duct by tracking another return to it. You want to make sure you don’t pick the duct that is feeding air to the house, but rather pulling air from the house. This was also fairly easy since I had the drop ceiling. In addition to finding the right location in the duct, I routed the path from the return location to the duct. I had decided that I would use the flexible insulated tubing instead of the metal tubing. This would keep me from having to put the pieces together and figure out angles and elbows. It also kept me from having to connect each of the metal pieces together, somehow, so they wouldn’t pull apart and from having to seal each of the joints between the metal pieces. I just had to ensure that the flexible tubing had a clear path that it could travel from the duct to the return.
With all of my locations worked out, I measured the distance between the location of the new return and where it would patch into the return duct. I actually sketched it out on graph paper so that everything was to scale. Since I didn’t really know what to expect when I got to the home improvement store in terms of supplies, I wanted to have something I could show someone if I needed help. With my plan in mind and my sketch in hand, it was off to the home improvement store.
The trip to the home improvement store ended up being fairly simple. In the heating section, I found a box of 25 foot flexible tubing that was insulated. I found a 6 inch metal piece that is designed to patch into the main duct. I found a return vent that had a 90 degree elbow. This is where the grille ends up being attached. I also picked up a couple of the closable grille covers. In addition to these main supplies I picked up a nice pair of tin snips for cutting into the return duct, some large zip ties for connecting the flexible tubing to my metal connectors and some cloth tape for securing the flexible tubing up in the ceiling so that it didn’t rest on my drop ceiling tiles. The total for all of this ran me about $50-$60. With all of my supplies, I headed home to start the installation.
The first thing I had to do for installing the return was to figure out how to mount the return vent and how to attach the grille to that. You don’t want any parts of this resting on the drop ceiling because it will cause the ceiling tiles to warp over time. Since the register vent is a fairly thin metal, it is easy to drill through it. I ended up attaching a piece of scrap wood to the return vent that was the same width as the space between my floor joists. I then just screwed this wood piece between the floor joists and I had my support. In doing this, you want to make sure that the vent drops low enough so that when you put the grille up against the ceiling tile, it fits nicely together with the hanging vent. However, you want to make sure it isn’t hanging too low that you can’t put your ceiling tile back in. I also attached two small pieces of scrap wood to the short sides of the return vent. This allowed a place for the grille screws to attach. Without these, the grille screws would only be going into the ceiling tiles and it could easily be pulled out.
Now, with the return vent hanging and the ceiling tile back in place under it, I cut a hole through the tile to match the inside size of the return vent. I then mounted my grille on the front. Now it was time to connect the flexible tubing to the return vent. For the most part, this is easy but it takes a little finagling to get it over the metal piece of the return vent. Once it is on, secure it with a zip tie. Make sure you don’t pull the zip tie so tight that you crush the metal.
At this point, I routed the flexible tubing along my planned path, securing it along the way with the cloth tape. You can do this just by stretching the tape across the floor joists and using a staple gun to keep it in place. Once I had the tubing running over to the duct, it was time to cut into the return duct and finish up the final connection.
Cutting into the return duct ended up being the most difficult part of the entire process. Since my drop ceiling rests right up against the bottom of the duct, I had to cut into the top of it. There wasn’t much room between the top of the duct and the bottom of the floor above it. Maybe 6 or 7 inches. You want to make the hole that you cut as close to the size of your connector as possible. Cutting too much leaves the possibility for a leak in the system. Not cutting enough either means you can’t get the connector in or you have to crush it to get it in. The secret to this just seemed to be time. I worked at this for the better part of an hour, all the while getting frustrated with the lack of space. I used the tin snips to cut the hole. I’m sure there is a better tool to do it, but a) I don’t know what that tool is and b) I probably couldn’t afford it if I did. Once I had the hole to the right size, I just dropped the connector piece down in. There are metal tabs that you can then bend over inside the duct to keep the connector from just pulling out. I also used duct tape to seal the seam between the connector and the duct. This was just to prevent any small leaks in the system.
Once the connector was on, I just attached the flexible tubing to it, then secured it with another large zip tie. Once that was done, I opened up the grille to activate the new return. It looked good, but I wasn’t sure if it was working or not. To determine if it was pulling air or not, I took a sheet of paper and held up just under the vent. The paper pulled up against the vent!! Success. All that was left now was to put all of the ceiling tiles back and clean up (a small feat in itself).
The one additional thing I did was to install the closable grilles on the additional returns in the house. This allowed me to create more of a draw from the room in the basement and less of a draw from the other locations. That meant more hot air being pulled and circulated through the house. Since installing the return, I haven’t had any issues (that I know of) with negative or positive pressure in the house. Given that the basement is mostly open and is also open via the stairway to the main house, I didn’t really expect to have any issues with this. I’m happy with the installation and I’m getting that warmer air circulated through the entire house.
In summary, here is a quick outline of the steps:
Plan – identify the location of the new return, where you’ll patch into the duct and your route for the flexible tubing.
Measure – You don’t want to get too little of the flexible tubing. Make sure you measure so that you can get enough without buying way too much.
Install the return vent.
Run the flexible tubing.
Cut into your return duct and install the connector.
Attach the connector and the flexible tubing.
Test the new return and adjust the closable grilles if necessary.
Here is a quick list of the parts that I needed:
return vent (6 inch round on one end, with rectangular return opening on the other end, with a 90 degree angle)
metal duct connector (6 inch round)
flexible duct insulated tubing (25 foot box – this was the shortest distance I could find)
scrap wood (for mounting the return vent and attaching grille to the return vent)
screws (for mounting the scrap wood to the return vent)
close-able grilles (I ended up with 3 total)
large zip ties (they sell these in the heating section with the flexible duct tubing)
cloth tape for securing tubing (also in the heating section)
Here is a list of the tools that I ended up using:
cordless drill (to drill through return vent in order to attach scrap wood)
utility knife (for cutting through drop ceiling tiles and for cutting flexible duct tubing to proper length)
staple gun (securing the cloth tape)
tin snips (for cutting into existing return duct. Use the drill to start the hole and work from there)
screw driver (attaching the grilles)
flashlight
ladder
