Hello all, I’m in the process of replacing my ac and have decided to go geothermal. I have the following 2 quotes Cooling load: 46k Heating load: 60-65K Quote 1: Good contractor, does a fair number of systems/yr Water furnace 7series 4ton (upgraded from 5series) 15kw electric back u 4x 200ft vertical wells, upgraded to 225ft (4.5 ton loop) Water heater add on Variable speed water pump Will add additional return duct $32k before tax credit Happy to take off $4500 to go with a 5 instead of a 7 series Will have to add several electric circuits for the heat, probably another $2k Quote 2: Good contractor, #1 in the area Water furnace 5, 6 ton No electric back up Vertical loop Possible horizontal (5k cheaper, wife doesn’t want the yard that torn up) $35k before tax credit Won’t need as much electrical work, but probably some My home is earth contact and has ductwork through the slab. The system is already air starved with the current 4 ton conventional system. Multiple contractors have expressed concern about increasing the system size due to airflow issues. I also have humidity problems that I need addressed with this new system. I’m inclined to go with quote 1 with a 7 series to handle the humidity. Per quote 1, waterfurnace recommends sizing the loop and system for cooling load in my area over full heating load. He was also the only one to seem to understand earth contact homes and the problems and benefits associated with it. I do have 2 large soapstone wood stoves to heat that I actually like a lot to use during the winter for extra heat. I plan to give someone money in the next couple days. Thoughts? Other information I need to add?
Size of home? Large load numbers for an earth contact house. Humidity problems year round or just summer? No way 6 ton system, At first stage it will be trying to push 4 tons of air through your already starved ducts. I would look in to solving humidity issues with building science/ ventilation system. If it's ground dampness shouldn't it be kept out rather then removed. Lots of info we don't know about your house. Does the conventional 4 ton have long run times as to remove humidity? Single stage?
The house is almost 4500 square feet with 80% slab on grade. Old windows and doors but 2x6 framing and insulation. Probably needs a bit more in the attic, but dying ac system moved it ahead of other improvements. I was planning to do this in a year or two. Earth contact to north and west side on the entire first floor. Humidity is mostly an issue in the summer. Humid Missouri summers. My current conventional system isn’t quite taking care of both humidity and total temperature, but it is over 15 years old and essentially unrepairable due to the refrigerant changes. We put down vapor barrier glue under the engineered wood floor on most of the first level and added vapor barrier for the carpet pad on the rest of it, which is helping. Replacing the exterior doors will help a lot with air sealing as well, but we haven’t been able to make that happen yet. One project at a time. Conventional system runs pretty much continuously from afternoon to dark. We let the temp rise during the day. It is a single stage. It’s a well built 30 year old house that needs all of its 30 year maintenance. New to us and working as fast as we can. New sealed skylights have helped quite a bit since they went in a couple weeks ago. Things keep breaking faster than the 5 year plan allowed for. Windows still seal, but are single pane and need replacing. Exterior doors need replacing as well. It’s just a matter of getting past urgent items like leaking skylights and failing a/c before we can shoehorn them into the budget. I’m glad someone else agrees that 6 tons is too much air. That was my biggest worry.
I would avoid someone who proposed a large system without accounting for or fixing your existing ductwork to accommodate. That basically means you would be stuck with a noisy system and probably a humid house in the summer.
What would be wrong with a (5) ton 7-series? It can throttle back to run like a 3 or 4 ton for cooling, You can slow down the blower, especially in heating to not go above 1500-1600 cfm, most of the time it will run less, and it can carry almost your whole heating load. What would be the downside?
Assuming I am reading things right, the water furnace 7 series has a capacity of around 60k btu for heating with an entering water temp of 55F, which is ground temp around here. I'm extrapolating from 58-60 for 50F and 62-68 from 60F on page 37 of the tech sheet for the water furnace 7 at 100% load. Assuming I can read the sheet correctly, a not inconsiderable assumption given my recent crash course in AC and geo system design. If my reading is correct, I shouldn't need back up heating except in an emergency or an incredibly cold day. Fortunately, it can come on for short periods at 5kw increments. I can always use my 2 soapstone wood stoves, which I like anyway. They'll put out 10-50k btu/h each. I absolutely need another return. I only have 1 10-12" return right now which is inadequate for even a 4 ton system. The 4 ton guys are going to put in a second return, which I think will help a lot. I don't think there is room for any more return than that. I am pretty surprised the 6 ton guys aren't looking at the duct work at all. I could ask for a 5 ton, but I'm not sure the cost would increase the benefit.
Your ground temperature will drop when you extract heat in the winter, count on having 30F in the middle of winter. What would be wrong with a 10 kw electric heat element, you should cover yourself not only for supplement heat, but also for a mechanical failure. Yes, you should get a larger return duct. Incremental costs of a 5 ton versus a 4 ton machine are minimal, everything else can stay the same. Depending on loop design and pipe size, a single variable speed flow center can do the job in either a 4 or 5 ton. The 5 ton will run smoother and more efficient.
That makes sense. When I put my manual J values in, the 60k heating load is assuming a exterior temp of 4F with internal of 70F, which is significantly colder than average. Average winter temps in KC are lows of 22 for Dec-Feb, so I shouldn't be using much if any auxillary heating, especially since my wife and dogs like to snuggle up to the soapstone stoves on cold days. I'm looking forward to a much quieter return system. It's pretty loud and right by my computer.
Add another return opening, or slow the blower down. Going with a variable speed unit also help, it will run at a lower stage most of time.
I went with the 4 ton and improved duct work. I’m waiting on install. Unfortunately it’s looking like I’ll miss all the big summer heat to really tell how the system does this year. Here is to hoping I didn’t choose poorly, but I think I used all the information I have.
Maybe you don't need the sqf since your are not loaded. But maybe this is the wrong place for shaming someone who is successful, worked hard or has the funds for other reasons, to fulfill himself the dream of a nice house.
