Isn't it better for purposes of calculation and comparison to stick with therms rather than worry with cubic feet? Therms more closely align with the ultimate goal - cost of heat delivered to structure.

Crucial, I think to figuring a basement load in a northern climate is knowing what insulation there is in walls, beneath slab, and footing perimeter, if any.

In mine the north and south walls are 1 1/2 pink foam (36' walls) the east and west (24' walls) are R13. All walls are block and the walkout is brickfaced.

I did not express it correctly, but i calculated it properly on the software (+-10% your cu' is near .137). I asked the question as calc software prices based on cu ft though i agree that a cu' of nat gas has a different btu value depending on provider.
When I have time I'll crunch your basement load for you. Is there wall insulation? Which direction do the windows face (N,S,E,W)? How high is the ceiling?
Your AC appears to be a 3.5 ton but higher in efficiency than I guessed.
I still surmise that we can't do your install by proxy, but I'll help where I can.

It's pretty basic 24 by 36. Wall down the middle. Laundry, bathroom, stairs on one north side below grade with one 3x2 window on the west side. And on the south side (walkout side) there is a 6x6 double glass door and two double windows 6x4 that face south. The north wall has 36 feet with 1 1/2" pink foam which is R7.5, the east and west walls 24 feet each is R13 and the south wall is just 1" so it's R5. All the walls are block and the south wall is brick faced. The ceiling is 7 1/2 feet.

Thanks Joe!

Sorry, can't make the 3 ton work effectively by my calcs.
j

Thanks for trying!

What size do you think it needs?

I think a 4 ton would probably do, but now if you're going to purchase equipment I must beg off and suggest you get a local guy with (here i go again) local experience. If he likes you for a 4T you could try larger electric coil with 3 ton heat pump and 4 ton loop system, and upgrade later.
Best of luck,
J

Since he already has the system, wouldn't he be better off trying to spend the money towards upping his insulation?

Is the problem going to be with both heating and cooling or mostly just the heating since it's the larger temperature change from inside to outside?

When I first starting thinking about this project I thought about adding the GEO and using my existing furnace / ac as the backup. Then I would just run the GEO as primary. Then I could just use two thermostats, one for each unit. This might just end up costing more money to run both, not sure.

You can't run two systems on the same set of ductwork.  

Not having seen the figures,  I can't say if the problem is heating or cooling.  I would guess cooling since you can always add backup heat to assist in heating.

Is there a local installer who can help you sort this out?

I'm okay with 4 T. Good question Seneca but I didn't do the load so I'm unable to calculate different insulation benefits (I entered provided numbers in to op cost software), usually differences are only 5% or so. I did mention that larger elec coil would work with 3 T, however, electricity is cheaper than propne but not necessarily N.G.
Still want the advice of the local guy and as long as you don't mind waiting he'll likely help you with the install.
Joe

I had a local guy out yesterday. He recommended the 4 ton system for my house.

He also looked at my 120,000 BTU furnace and said I could probably drop down to a 90,000 btu.

I don't have the $ to upgrade to the 4 ton so I am pondering some different options:

1. Just keep my current furnace and just pay the higher bills until I have the $ to go to a 4 ton system.
2. Downsizing to a smaller gas furnace that is better sized for the house
3. Take the risk with the 3 ton system with 4 ton in the ground and strip heat and paying a little more during the peak seasons but hopefully average out over time. .

One other question I was wondering is if there is a way to reduce the BTU on a furnace from 120,000 down to 90,000. Could I swap out the burners?

Any last words of wisdom?

Thanks,
Pete

Appreciate the local guys thoughts. I'm not bothered by 4 tons in the ground and a 3 ton heat pump, but you have to have a big enough auxiliary coil. Remember projections are based on a 20 year average, if we have a few mild winters you'll win; hands down. If we don't, you'll still spend less than heating with propane. Bank your savings and get the ideal system later.
J

He is going to include the new heat strip as part of his estimate.

Are these measured in KW?

Just so I have something for comparison, what size would you recommend for my setup?

Thanks!

Heating strips are usually rated in KW, but just like a meter and foot, KW converts to BTU/Hr, which is what the tons come from. Basically 1 Ton = 12,000 BTU / Hr = 3.5 KW. Of course electric heat coils are cheap. It's probably the easiest (useful) circuit to build, and basically operates at the same efficiency whether you oversize it or not. He may put in as much as 10 to 20 KW worth of them so that you don't end up wanting on the coldest day (geothermal systems are generally designed to cover 90% of the coldest temperature because the payback on heating that last 10% of time isn't worth it).

If the strip heat was changing the temperature 10 degrees would it work out that a 10 KW would run for X minutes and a 20 KW would run for 1/2 of X minutes? Does that work out so the cost to run is about the same? Or is it more a factor of air flow. Do you need to circulate enough air to make the temperature change so one would end up running more than another?

For strip heat, the device should have adjusters on it, so that if you have a 20KW strip but only need to run 10KW, it will only send 10KW of power through the system. It's one of the beauties of electricity - all electrical devices are 100% efficient at creating heat. Now for a central heater, strip heat does have a ~95% rating because while it makes heat, it doesn't all go where you want - you have to circulate it. Like I said, it's a very simple circuit, pretty much a resister stuck in the middle of a wire. Generally, probably each 5KW or is a "resistor", so it needs 5KW, run heat through 1 set. Need 20KW, run through 4 circuits. Now, if your electric company gives you only a whole house rate, and not a separate meter for the geothermal+electric heat, you're probably best off heating to 60 or so and using space heaters at the places heat is needed when running electrical. A space heater is considered 100% efficient because it heats the room it's meant to. That would let you perform your own version of zoning. Although I'd double check all of it with your local person. I'm not even one of the geothermal installers on here, just someone with a lot of interest and a geothermal system in my home starting next week (barring rain and anything else that can go wrong (and no Joe I'm not complaining - I do need to use up that propane so better to get to someone who might actually freeze)).

10K marginal, I like 15K best. 10K would work 90% of the time.
J