It was -9 F this morning when I got up, and my yard is still covered in this weekends 6″ of fresh snow.  It seemed like a good time to talk about HVAC systems. The space that I am renovating was a garage converted to an addition. For some reason, the people who did this renovation didn’t connect it to the central heat and air system, so they relied on window air and space heaters. The issue is, this room opens up directly to the main living area, so my living room/dining room/kitchen tend to be cooler in the winter than I would like, and I imagine hotter in the summer (though I haven’t been in this house through a warm season yet). Today’s blog will walk through how I decided on my method, and how I added HVAC to my addition.

Rating (decode with the handy-dandy guide here)

• Time 
• Money 
• Tools 
• Experience  
• Strength 
• Risk 
• Suckage 

Tools:

Step 1: Do Your Research

I’ll start this by saying there’s a reason HVAC professionals exist. They know how to run the numbers and determine the current load on your existing system, and if it can handle an additional branch. I took a bit of a chance here, as I didn’t run the numbers or consult an HVAC professional. What I did do was identify a room I was okay shutting off from HVAC as a sacrifice if my existing system couldn’t handle the new room.

The branch that extended closest to my new room only had two other vents on it, one to my laundry room in my basement, and one to the dining room (next to the addition). I guessed this system could probably handle an additional room on the system, but if it couldn’t, I would shut off the vent in the laundry room since it is in the basement and is naturally temperature controlled. This risks letting humidity build up in the laundry room, but I run a dehumidifier in the basement to mitigate that risk.

If your existing HVAC system can’t handle the load from a new room, or you don’t have a way to route the ducting into the new room, there are alternatives. If you live in a cool area where heating is your primary concern, rather than air conditioning, baseboard heat is an economical alternative (though the cost of running electric baseboard heat might surprise you). If you live in a warmer area where you need some heating and some cooling, heat pumps are a great alternative. They make small, single room systems, called the “mini-split” that can be installed pretty easily, and won’t break the bank.

Step 2: Determine the Location for Vents

Now that you’ve determined your existing HVAC can handle the new vents, you need to determine where to put them. It’s pretty standard to have them in front of windows. Windows are cold, so having the heat near them helps keep the whole room a more consistent temperature (and reduces drafts). Having the vent near a window also helps reduce moisture around the window.

My room has a giant window that I placed the duct under. I haven’t fully decided what I want this space to look like, so I actually ran one across the room to an interior wall as well, with vents I can open/close depending on my final design.

Step 3: Lay Out and Connect the Duct Elements

I used flexible duct since it is WAY easier to navigate around under my floors than rigid ducts. I started using insulated flex duct because of the length it came in (I only needed about 6′ of duct, the non-insulated duct came in 25′ lengths). I put the duct boot where I wanted it, then taped the flexible duct onto it.

Step 4: Frame in Your Vents

Wherever your vent is, there will be a hole in your subfloor. This will weaken it and if you are doing tile, you want as rigid a floor as possible. You’ll want to frame in around the vent so that you have something to attach the duct boot to. They have products that make this process easier for beginners, like the speedi-boot, but I have my whole floor open so I went with cheap since I can easily access everything around the duct boot.

This part will vary depending on your configuration. I have approximately 14″ between the bottom of my new subfloor and the top of the slab underneath this. Therefore, the largest framing member I could use was a 2×4, which is probably adequate for most projects. I tend to over-engineer things, so when possible I will use scrap 2x6s or even 2x10s. I cross braced between my joists, spaced the size of the duct boot across. This is a 4″ x 10″ register, so I spaced my 2x4s 10″ across.

Then I pulled the duct boot flush with top of the frame and put a cross beam between the two 2x4s to finalize the frame. I used a couple roofing nails just to secure the duct in place, but you can use whatever fastener is available.

Step 5: Connect the Flexible Duct to the Main HVAC System

Now that the register is connected and frame into the floor, it is time to connect the flexible duct to the main HVAC system. For me, this involved punching a hole through my rim-joist to connect to the main duct in the basement. This step will vary wildly by your house set up, so I won’t detail it here. The square box in this picture is where I connected to the main HVAC system.

If you’re connecting to a duct like this, they make something called a “take-off” that will allow you to connect your flexible duct to the main duct. Use your take off as a stencil and mark the main duct where you will need to cut it. I made a starting hole using a hammer and nail, then used tin-snips to make the hole the correct size. Insert the take off into the hole and push the metal tabs out to secure it. Finish it off with a few layers of duct-tape. Now, just connect your flexible duct to the take off!

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