Happy to see this subject brought up although I'm sure most building new, didn't make it this far. I think the OP got "shorted" but no worse than most building new in this current building climate. With such a hot market one has to be careful they don't spook the best or only opportunities. I think it's important to get a 2 stage system as a minimum. Getting a properly sized system is much like getting a building envelope to perform at current levels of international energy code. For most people, the best chance is to hire a design and building team who already understand the details from past projects. At this stage of the game it's often too late. Ductwork in a vented attic or low levels of roof deck insulation can effect cooling loads as much as western windows depending on the details. Martin Holladay has the best articles on this topic. Calculating cooling loads and When do I need to perform a load calculation? are free while Who can perform my load calculation? is behind the paywall but relevant here. When builders get experienced with a particular plan, the need for load calcs diminish. For custom designs costing hundreds of thousands, using a third party to help with design, sizing and commissioning can be a wise investment. Some architects and builders include this with their services. Energy Star is the most common way to achieve a better level of verified performance. This goes beyond energy use to include comfort, indoor air quality and durability. The program ensures bath vent fans, outdoor air ventilation systems and kitchen vent hoods are installed properly. With a reported energy savings of $300 a year, simple paybacks are reasonable. Not all HERS raters do load calcs but most can point you in the right direction. If you only care about HVAC system design, hiring the right 3rd party can help. If building in the south, try Allison Bailes with Energy Vangaurd. He has influenced the need for better rules of thumb, like 1 ton per 1000 sqft for homes that meet international levels of energy code. This can be useful when comparing results to what the HVAC contractor wants which is typically closer to 1 ton per 500 sqft. I find HVAC contractors more willing to install smaller systems when they have stamped letters from a mechanical engineer, which in our case is the HERS rater.

I looked in there with a flashlight and it seems to be cast iron and a pipe bringing the air up from the system below (it looks like the inside of a stove). This appears to be fit into the chimney space. As @Austin Air Companie pointed out this is exactly what I am hoping to do. It appears I just have to find the right professional with this knowledge. Well be careful in that, because what you likely have is some heating only channel in which they probably used natural heating principles to heat this home with. (Heat rises from the heating apparatus in the basement... due to age of the house this was probably not a forced air system like we have today.) Forced air requires more room as air takes up space if that space is not there it leads to a whole assortment of various problems. Then you throw in air conditioning another modern thing that wasn't there when the house was built. 400 CFM of air per ton of air conditioning. 3 tons that means 1200 CFM. 4 ton 1600 CFM, 5 ton 2000 CFM. Not only supply air, but also return air. Measure the entire cavity, it will tell you in quick fashion. I really doubt the cavity of the chimney is large enough to do what you will require to get this to work.

I completely agree with Fudd (and would have used a stronger word than "baloney.") Any company that won't do a "Manual J" load calculation on your home should NOT be hired to install your new system! Here is a good explanation of why doing a load calculation is so important: https://www.pvhvac.com/blog/why-the-manual-j-load-calculation-is-key-to-hvac-design And a 96% efficient furnace is definitely preferable to the 80% offering (in which 20% of the gas you purchase to make it run -- is wasted.) In this day and age, please go with the furnace that only wastes 4% of the gas you purchase. Even your gas utility bill with thank you, with lower monthly costs to run your new furnace (than if you'd bought the 80% efficient version).

I'm disappointed that what had at first seemed a very balanced comment was followed by what seems to be misinformation and misdirection. People buy ground source heat pump equipment because they want to and can afford it. Or decide they need to in their locations. They're hugely more expensive than alternatives, which is why they're still not very common. "When’s the payback on a Tesla? People still choose to buy them for reasons other than the ‘bottom line’." Not a comparable. A false analogy. "I would not choose natural gas or propane for reasons relating to the environment, safety, IAQ & paying for yet another utility hookup for an energy source that might not even be used for months on end during the year." What effect having a gas furnace has on indoor air quality. Another hookup? Most people prefer gas cooking appliances and besides, the OP is talking about an existing home, he either has gas service or he doesn't. "Rather than spending perhaps tens of thousands of dollars on a Solar Array, I would sooner invest that same money, hopefully less, in a ground loop for a Geothermal system." Sure you would, that's the business you're in. The ground source heat pump market is not growing as expected by those in the industry, which suggests that your opinion isn't widely held or easily sellable. In many parts of the country, solar panels can have a quick payback. Not so ground source heat pumps. "I often hear about Solar Panels when geothermal is mentioned, as an alternative way to save money by creating energy." In a place like Texas, where electricity is cheap (other than during cold weather crises as they just experienced) there's likely no payback from a solar panel installation. People do it as a personal statement, call it for environmental or other personal reasons. Like buying the Tesla, not a financial decision. An HVAC system blows warm air when it's cold, cool air when it's hot. It's one of those things people don't care about - either it works or it doesn't work. Spending extra money for an exotic system doesn't equate to extra payback when the home is sold. Neither owners, nor visitors, nor people passing by, nor anyone else, concern themselves with what's doing the work. It's equipment that doesn't produce an experience for someone in the house if it's working. In the US, there are vast areas where electricity is cheap. It will remain so for some time. People don't spend money today to potentially save money 10 years out when market conditions may or may be different. I suspect you could build a house with mahogany or teak framing. Or you could paint the framing bright colors. Why bother, you can spend less money and effort and get something else that will do the same job. "We almost never use setbacks at our home - even when going on vacation for weeks on end with no one home, our geothermal just runs." You're combining two different things to produce confusion. Thermostats that have a setback feature ALL are set up to provide lower overnight temperatures to have more comfortable sleeping conditions and then a recovery in the morning before wakeup time. As sleep specialists recommend. That in demand comfort features isn't possible with ground source heat pumps because the warm up period from a setback is too slow to be convenient to use, absent triggering a secondary heating source (like a furnace) to help. THAT'S why you don't "believe" in setbacks with a heat pump - they don't work. Turning down a thermostat during heating season when the home will be unoccupied is not a "setback" as that word is most commonly used. It's done to save money, why heat a vacant house? No setback thermostat is needed, even a dumb 50 year old analog thermostat can be turned down.