HVAC solutions when space is at a premium
I own a 1950s ranch in a nice Chicago suburb. We live here for the great schools, however the neighborhood is exorbitantly expensive. Moving to a bigger house would literally cost an extra $300-$400K. Consequently there is a strong desire to make this house work for us. That means our basement is hugely valuable living space. We are a family of 5 in a smallish ranch so the basement is truly the house's saving grace. The kids love it as is but it is not fully functional space for adults because of the massive ductwork (6' wide spanning the entire length).
With that in mind, I'm trying to determine the best solution for our HVAC. Both AC & furnace are dinosaurs and need replacing. Windows are all new dual-pane vinyl. Last spring I spent a weekend in the attic caulking/spray foaming any ceiling openings. I then rolled out R-30 insulation over the existing batts. The walls are brick and block with little/no insulation. To improve the wall's insulation I've thought about rigid foam over the existing plaster, then drywall but that is not a high priority. So the home's envelope is a mixed bag of good & bad.
I've been delaying replacing the air handler/furnace/ac because I really want to find an ideal solution that can eliminate the basement ductwork. My goals are 1) energy efficiency 2) comfort and 3) improving the basement's functionality so adults could be down there comfortably. The last goal is fairly important because our basement gives our family of 5 an extra 1,500sqft of living space in a 2100 sqft house. It's not the end of the world if the ductwork stays but if there was a smart way to remove the ducts I would absolutely pay a premium to have it.
I have been increasingly thinking of the following solution:
1) Mitsubishi or LG Mini-Split system for cooling (8 indoor units in basement & main floor). Could also be secondary heat source.
2) Rip out the ceiling drywall in the basement (it's 1/4", sagging and needs replacing anyway).
3) Install Radiant floor heating using a between the floor-joist retrofit. My thought is the heat source would be a dedicated hot water heater (not a boiler).
4) Tear out the duct work to make our basement more functional.
5) Put up new drywall once complete, giving us a 7' ceiling height throughout the basement.
This is definitely not the easy or low cost solution and I'm wondering if I'm crazy to consider it? I'm guessing a professional installation like this would be $30K+. Consequently I'd have to do a lot of the work myself (which I don't mind). I'd probably install the minisplit this year with the only professional work being the coolant charge. Next year I'd work on the radiant (keeping the existing furnace until then).
My final concern is whether this design would adequately heat the basement (could the PEX between the joists heat both floors?). If I need to retrofit radiant in the basement floor as well it probably tips the scale against this. I'm crazy but not insane. There is a tipping point when I decide to live with the low basement ceiling.
I'm open to any ideas. Moving the ducts to the attic would be an option but in a northern climate that seems like a childish/selfish way to get some headspace. Am I in fantasy land thinking I can find a reasonable solution that is comfortable & efficient while also making the basement a lot more adult/tall person friendly?
Re: HVAC solutions when space is at a premium
I think your questions and inquiries are valid, and I think you're going about it the right way by trying to obtain the most info you can get before jumping into what sounds like an extensive project.
I would recommend you get two to three local heating contractors to look at it, and explain to them, as you have in this post, exactly what you want (Yellow Pages: "Heating Contractors"); after listening to your project ideas & goals, I think you'll be quite surprised as to the different ways in which different contractors may recommend attacking this problem, that none of us here might not even think of, and still remain in the present square footage of your building, and within your budget.
For example, it may be possible to remove only the large ducting in the basement and retain the branch ducts so that modern (much smaller units) for forced hot air heating and AC can make use of the existing ducting---you'll find that all modern HVAC equipment these days has shrunk in size dramatically, and has also become markedly more efficient in heating & cooling capacity in the process.
Insulation is always a good idea, and is a good news to see you have already taken positive steps in installing new double-pane windows & added insulation---so far, you're doing all the right things, as this will dramatically reduce the cost of heating, as well as the cost of summer cooling; if the basement is sub-grade (exterior surrounded by soil) it may well need less insulation than the exterior walls in the rest of the house.
I have my doubts that radiant would be enough to heat both 1st floor & the basement, but wait & listen to suggestions the heating techs make on this as well; radiant installs usually like to take advantage of burying the PEX tubing in "large mass" structures, like the concrete of a basement floor, but since in your case, the floor is already there, it would be expensive.
Always get a WRITTEN ESTIMATE PROPOSAL of the quote for the work the HVAC tech intends to do, and I would also suggest getting at least 3 estimates from 3 different heating contractors, so you can minimize the amount of $$$ you spend on this project, as well as eventually clarifying your mind as to the best path to take on this deal----it's always primarily first about determining which way to go, which path to take after taking the time to listen to several experts, until you're pretty well set in your mind that you've found the best way to go.
I don't feel it's a good idea to rely on a wall-hung water heater or the similar "boilers" some contractors are installing these days; I'm a traditionalist that thinks the modern small size of the newer floor model furnaces/boilers will still leave you adequate room for family basement activities, and provide you the heat & cooling you will need for a relatively large house.
If you're saying you have 2100 s.f. of house size, plus 1500 s.f. of basement size you would probably need a furnace/boiler in the range of 126,000 btu/hr to 140,000 btu/hr, the new insulation will help reduce this number considerably---make sure to tell the heating techs that you have added extensive insulation, and have added double-pane windows throughout the house---they should be doing a HEAT LOSS CALCULATION using these new factors to determine the new heat loads and cooling loads the house now requires.