Product

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Fresh Air Return Filter

• Scope: After moving into a newly build house, I noticed a large insulated vent hanging from the ceiling. After tracking it back through the floor joist and saw that it terminated through the wall, it was apparent that this was the fresh air makeup vent for the entire house. For those of you who do not know much about modern HVAC, fresh air makeup vents are used to not only bring in fresh air, which your house needs, but to also prevent fires from occurring with combustion based appliances. A good example would be a gas water heater and a dryer. Both appliances have induction motors that force air out of the house…but that air has to come from somewhere. ie. When you turn on your dryer, it sucks air from inside the house, through a heat exchanger, and then outside, same with the hot water tank. Now, without the fresh air make up, the appliances fight against each other like two people sucking on the same straw from either end. The appliance with the stronger induction fan will pull the flame backwards from the other unit, also dubbed “roll-out”. So if the dryer has a stronger fan, then the flames going upward and out of the hot water tank are now being sucked backwards and you could potentially see the flame coming out of the bottom of the hot water tank. Now this is an extreme condition where the house is truly air tight and several safety features of your modern appliances fail to work….but it can happen.

You can see the black, insulated, makeup vent hanging from the ceiling to the floor. (Not my house, but they are all pretty much the same)

• My problem fruitioned when I noticed a lot of dirt and bugs in my basement…plus in the wintertime, the amount of cold air coming in was insane. Knowing that I could not cover the vent, I initially dropped the end into a 5 gallon bucket in hopes of slowing down the convectional currents. Then I tried to tape some fabric over the end to keep the bugs and dirt out but that was a failure because of the amount of bugs and that loaded up into it eventually clogged the cloth. My final attempt was going to have to be engineered as off-the-shelf solutions were pretty expensive and not exactly what I wanted.

• My “at home” solution was to 3D print a custom manifold that used hose clamps to attach itself to the insulated vent. The vent would house 2 common style filters that had the lowest risk of obsolescense, cheap, and effective.

• I ended up using 2 new HEPA filters from a Rigid shop vac. Come to find out, several Rigid models and other manufacturers use the same style filter that they rebrand under their own name. The fliters friction slipped onto the end of the manifold and I mounted it upright to slow down convectional currents.