I have an 1800 sq. ft. 2 storey in central Ontario. My contractor is quoting a Climatemaster 5 ton, split system to work in conjunction with my existing oil fired, forced air furnace. I have read a good number of postings here and am concerned that the system is oversized, but if it isn't, I am sceptical that the 1/4 hp fan in my oil furnace is up to the task. I had him quote a stand alone system, as well and that is a 5T Climatemaster as well, but when I check with climatemaster.com I see that they use a 1hp, variable speed, DC fan. Any advice aside from "get another quote". I live in the middle of nowhere and getting a contractor here is worse than a root canal. We have frequent pwer outages and have to run on generator. That is why I want to retain the 74000 BTU/hr oil furnace which does a splendid job of heating the place when we aren't running our 2 wood stoves.

geothermal systems are designed to have a more airflow due to the cooler air coming through the vents, the fan in your current furnace likely isn't going to provide adequate airflow which will mean your unit will not be as efficient as it could be, also a 5 ton unit is for sure oversized my house is a 1800 square foot bungalo in Niagara Falls and on here the consensus was to go with a 3 ton unit. I decided on a 4 ton but that isn't the point I think that a 2 story is probobly easier to heat than a bungalo just due to the smaller roof so a 5 ton system will be too much, running it into your current furnace for the fan seems like a way to take an efficient system and make it work horribly and if you did go with a 5 ton stand alone system you would probobly be in a position where your ducts aren't adequate for the airflow provided by a unit that size. Bottom line is you need to find a new contractor

Thanks newdeal. I read your story with interest due to the similarity in size and your proximety. 3 tons was the size I came up with after surfing the net on the subject and before I talked with the contractor. However, this contracter came highly recommended by a neighbour and I'm trying to give him the benefit of doubt. He did his heat loss calcs and got a 68000 btu heating load which sounds unrealistic to me in that the 74000 btu furnace will snap the inside temp from 50 to 70 degF in a hurry when we return from several days away in the dead of Winter. More info: Our 2 story is easy to heat. It has a 2 story, cathedral style living room and the master bedroom opens off a balcony on the second floor. There are no heating ducts on the second floor. Heat finds its way up quite well. The house is well insulated and tight. The negative is: We are on windward side of a lake and 2 sides of the house facing the lake, have a lot of glass. Approximately 50% of the wall area.
He used a winter design temp of -9F, which is maybe a little on the warm side. We are ~50 mi north of Belleville and the temp drops fast as you move away from the lake. Where you are, you get really good moderating effects from the lakes. Also, you are south of Lansing.
I got off the fan topic: No matter what the sizing of the heat pump, I doubt that my furnace fan is adequate so what to do?
My first thought would be to rerofit the fan in the furnace but that might not be doable (Kerr compact furnace). So what about an air handler of sufficient capacity on the top of the furnace with the heat pump coil?

no idea what to do perhaps someone with experiance with this can chime in. As far as the heat loss goes that does seem very high so I would get a second opinion. Then I would download the geodesigner software from climatemaster and plug in some numbers to see the cost of the differant units to operate. Also as a rule of thumb a 6" duct caries 100cfm and a 5" duct about 65cfm so count how many vents you have, measure the diameter of any you can see and see how many cfm your ductwork can handle. If you have no ducts on the second story then your probobly not going to have more than 14-16 ducts and a 5 ton unit puts out like 2000cfm in stage 2 so it will sound like a wind tunnel in your house

Curiously in spite of my 3 ton recommendation for newdeal, I like a 4 ton for a split, because we are no longer using auxiliary heat, we are using emergency heat. That matters as you are replacing not augmenting geo. Hopefully contractor suggested blower upgrade. Try looking up an ECM motor.
Joe