HVAC over Minecraft…Uh-huh


Now granted, my 6 year old has just been introduced to Minecraft running on our home-built Raspberry Pi. He is just at the “whack away at anything” stage. And yet, both he and his younger brother were much more interested in talking about our newest project: Geo-thermal HVAC system expansion than spending time playing Minecraft.

Imaginative Playspace
My boys enjoy hours of imaginative play in our unfinished basement. The story lines vary widely from pirates and construction workers to police officers and crooks. We design and build wood projects, 3d prints and even paint, color and draw art down there. All is good…well, except that our use of the basement is seasonal. This is because when we installed our 3 ton Geo-thermal HVAC system, we intentionally chose not to condition the unfinished basement.

I Love My Geo-Thermal System
I love my Geo-thermal HVAC system, but it wasn’t an easy choice to install. The upfront costs were very prohibitive and were it not for federal and state rebates, there isn’t any chance I’d have opted for a Geo-thermal system. But 3 years later, I’m so glad I did. The system is super quite, with no external A/C compressor and both the heating and air-conditioning systems are self-contained in a single air-handler in my basement utility space. I also plumbed a “desuperheater” to the hot water tank so that the heat generated as a by-product from the compressor is used to heat my household hot water.

That being stated, when the installer ran the “Manual J” to model the heat-load for our New England home they came up with a recommendation of installing two units one 3 ton system in the basement and a second 2 ton system in the attic. When I receive the Manual J hardcopy result, I could see they obviously stuffed bogus information into the software tool just to satisfy the requirement to run Manual J and that it wasn’t even close to representing the actual design of my home. Let me tell ya’, there ain’t no way I would have:
a) been able to afford two units even with rebates.
b) been okay with the idea of two separate HVAC systems in my home

So, I leased a copy of ACCA accredited Manual J software to model the heat and cooling loads myself and came up with a very different story. Ultimately, and with the HVAC contractors full agreement and support, I decided to spend some extra $$ upfront in beefing up the R-value of our insulation in strategic locations of the home and install a single, 3 ton HVAC unit in the basement. As you can imagine, I was really concerned our first winter wondering if the Geo system would have enough capacity to carry the heat load. Now, after two winters (one of which was a record-breaker for low temps and high precipitation), I’m convinced I did the right thing. The question remains; Does the existing system have enough capacity to condition the basement too?

Always Pushing the Envelope
Coming back to our Minecraft trumping project. When I first mentioned to the boys I was planning to heat and A/C the basement, it held no interest for them. I hadn’t reached out to them in a way they could relate to the problem and grasp the benefit. So, I began to chat with them about their current basement adventure [creating a haunted Halloween storefront] and wondered aloud whether or not their storefront would get many customers if it was a cold wintery day outside. Their answer was, “no, it would be too cold in here!”. Hmmm, so what if we were able to heat this area during the colder months, would that help business? “Yes!”, they replied. From this point forward they were hooked and engaged on the project.

HVAC ducting plan
HVAC ducting diagram – as drawn by my 6 y.o. son

Measure Twice – Cut Once
We began our project – as we often do – by stating the problem; In the winter months it’s too cold in the basement to play. In the summer months, it’s really humid and sometimes kinda hot in the basement and uncomfortable. I’m fond of reciting to my boys the old adage, “measure twice, cut once” throughout the projects we share. In other words, check and recheck your plans before committing. At the beginning stage of the project I related this adage to the notion of creating a ducting layout plan. By drawing a plan, we have an opportunity to “what if” our routing to see if we discover any potential problems or barriers. We also generate a “bill of materials or BOM” to estimate the materials, quantities and costs of what we need to buy.

Our first draft duct layout plan is shown below with a rough estimate of materials. The shaded duct is an existing return duct we’ll need to tap into. The “ribbed” lines are 6″ dia. flexible duct branches to the proposed register vent locations. The big white duct is the 12″ dia. trunk line. We used one of many useful websites for understanding the airflow requirements vs. square footage math and calculating the proper duct diameter size given the size of our projected conditioned space (i.e. finished square footage).

HVAC duct layout plan and BOM
HVAC duct layout plan and BOM

Once we were satisfied with our duct layout plan, I ordered all the materials online. That’s right folks, 100% online and shipped to my home. I found Lowes to be the least expensive by a few dollars a product, but when they did not carry the needed item, I second-sourced through HomeDepot. Both have ~$50 minimum for free shipping (within the continental U.S.). Lowes offers free return shipping which is consistent with what I believe is their superior customer service, support and satisfaction.

How is a Forced Air System Like a Balloon?
Once we had our duct layout plan we printed out a copy, sat in the middle of the basement and looked up into the ceiling joists to find the existing duct work. I pointed out the trunk and branch ducts which fed our first floor rooms. I pointed to each branch and asked them to tell me which room on the first floor the branch fed. This was a fun game, but also promotes visualization and spatial relations skills considering they have to resolve in their mind where each room is on the floor above them.

During this exercise a great question came up; “What is this other duct that goes back to the HVAC, but doesn’t have any branches?”. Great question, this is the return line. Now communicating the principles behind forced-air HVAC systems was a bit more than I wanted to dive into. But I was able to clearly communicate the idea by using the analogy of blowing up a balloon. In my analogy I asked;

Me: What happens when I blow air into a balloon?

Boys: It gets bigger.

Me: Can the air get out?

Boys: No, it stays in the balloon. Unless the balloon explodes.

Me: Think of each room like it’s a balloon. What happens if the balloon is too strong to explode and you keep trying to blow air into it?

Boys: We get really tired and stop blowing.

Me: So, no more air can be pushed into the balloon now matter how hard you blow, right?

Boys: Yup.

Me: Same thing happens with the HVAC system. We need to give the air a way to escape so the room doesn’t fill up like our balloon. This is what the return duct does. It allows the air to come back to the HVAC system and when the air comes back, we heat/chill it some more and send it back to the room again. Over and over again until what happens?

Boys: The room gets hot!


In The Zone
Back when my Dad decided to condition the basement in my childhood home, they had a single thermostat [zone] for all three living levels. That same single thermostat serviced every living space and bedroom. Generally, this method worked well given each living space had similar thermal characteristics (number of windows, doors, people, etc.). However, if one room or living space differed substantially from the average, you end up with a cold or hot spot you could not effectively address by changing the thermostat setting. Do you remember using space heaters in the winter and fans in the summer? Now you know why.

Back in my Dad’s house, we cranked the little handle on the register vent to turn on/off the heat. That was our “zone controller”. These days multiple zones within a single home are more common. So, what is a zone?

Simply stated; a zone is a grouping of living spaces that are serviced by their own thermostat. The thermostat for that living space controls the heating/cooling delivery to that specific area in the home. How does the furnace know where to send the heat, you might ask? It’s managed with what’s called a controller [small computer] and an electric damper. Let’s walk through a simple list of steps in the process. For ease of description, let’s call our living space Zone 1.

  1. Thermostat “calls” for heat when the temp in Zone 1 gets below the temperature you set
  2. A controller [computer – see pic below] receives the call for heat from Zone 1 and sends two signals to your equipment which:
    1. Turns on the HVAC equipment (furnace and fan in our example)
    2. Opens dampers [see pic below] to the ducts that run to vents in Zone 1
    3. Closes dampers to the ducts that run to vents that are NOT in Zone 1 (with exceptions, which I’ll cover later).

Our system HVAC system has 3 zones. Two on the 2nd floor (bedrooms) and one on the 1st floor (living, dining, kitchen, etc.). If designed properly, multiple zones can reduce the overall load on the HVAC system. Because our basement space has a very different thermal characteristic (external walls, cold floor, glass slider door, many windows, etc.) than the rest of the conditioned spaces in the house, it really should be a separate zone. Unfortunately, the zone controller installed with our Geo-Thermal system was only able to manage 3 zones. This is bad, but not to worry…hardware hackers to the rescue.

Too many choices
After an extensive internet investigation of our zone controller options and capabilities versus other similar zone controller systems, I found I could add a module to our existing EWC controller to get 1 more zone (bringing a 3 zone system up to 4 zones). Or, I could replace our existing zone controller with a newer model made by a different manufacturer which is capable of controlling 4 zones without an extension module. The decision came down to a cost vs. benefit analysis.

Upgrade existing zone controller with an expansion module:


  1. Time: Easy to add module (connect data bus cable, then wire up new thermostat and damper)
  2. Cost: Slightly less expensive ($150 for extension vs. $180 for new zone controller)


  1. Features: Old controller is a very basic system with few features. It’s not so easy to work with if you’re trying to figure out what’s going on with your HVAC system. This wouldn’t be a big deal with a gas, oil or electric furnace, but with a Geo-Thermal I found myself wanting as much operational information as possible.
  2. The expansion module only supports 1 zone. If I needed 2 zones in the basement, I’d need to add yet another single zone expansion module at near the same cost of a full-up, 4 zone controller.

In the end, I decided to replace the existing 3-zone controller with a new 4-zone model. I consider the new features and flexibility worth the extra investments in time and cost. One of the most satisfying features of the new controller is a digital display of the temperature inside the unit at the base of the duct. Now I can tell if the unit is cooling or heating without running upstairs and putting my hand on a register vent trying to sense warm or cold air.

Next time…Let’s start hangin’ some metal!