Correct sizing for new geothermal system

[vambo]

Hi,

My current tri-level 2400 square foot home in north east Ohio has a 3-ton Trane XL1200 heat pump that has worked well but I’m planning on replacing it with a WaterFurnace Envision unit. The first contractor inspected my current system, including the duct work, and recommended the 4-ton unit using 4 wells at 125 foot deep. His heat loss calculation was 60,000 BTUs.

The second contractor paid a lot of attention to my duck work and told me that the 4 ton Envision unit would have too high of air pressure for my duck work; he suggested a 3-ton unit but he would still go with 4 wells as that would “increase the efficiency” of the system. His heat loss calculation was 51,000 BTUs.

Does it make sense to go with the 3-ton unit with the 4 wells? I thought that the variable speed air handlers in the new units could compensate (somewhat) for the duct work?

Thanks for your help.

[dwaynew612]

I'd strongly recommend having him show you the manual J ( heat gain/loss calcs) this takes EVERYTHING into account, wall exposure, shading, insulation, window construction. This is the only way you will know what size you need.

As for duct sizing, Have him do the Manual D calcs this will show you the exact CFM required for each room. If it's already enclosed you most likely have to live with it if it's close, if it's too far off you won't have the best system you can.

The new ECM ( variable speed ) motors do help maintain static etc. but if you don't have the right size ducts you can't get the air to the rooms. Too small static will be too high, too big not enough static. All of which affects efficiency. If possible being a multi level house you might think of a zoning system. It would help even out temps.

[vambo]

Thanks for your response. I agree with everything you said about the Manual J and Manual D. But for the point of discussion, let’s assume that the heat loss in my house requires a 4-ton geothermal system and that the duct work is undersized for the air flow requirements of the 4-ton system. Does it make any sense to use a 3-ton geothermal system, with ECM motors, and the vertical well system for the 4-ton unit? I would think that it would not be able to keep up with the heat loss in very cold conditions.

Or does it make sense to go with the 4-ton unit and hope that the ECM motors can compensate for the undersized ducting?

One more question. Why do contractors say that my house requires a 3-ton air sourced heat pump but a 4-ton geothermal heat pump? Isn’t a ton a ton?