Hi All, I am a homeowner and have gotten several bids on a new geothermal system to replace my gas furnace which is about ten years old now. Both companies proposed horizontal loop systems that appear fairly almost identical in design. They both also recommended the same Climatemaster five ton unit. One company wants to leave my ductwork as is and the other wants to make significant modifications to my ductwork in the basement. They say that my existing ductwork is not large enough and the geothermal will be noisy if it is not changed. I really don't want to change the ductwork, because that would involve ripping apart my finished basement which I have hundreds of hours of work in. What should I do? Is there another geothermal company that has something that would be more suitable to the ductwork that I have? Thanks

The outfit that wants to swap your ductwork is likely on the right track. Typical forced air furnaces heat air by 60*F or more, whereas geo only heats air by 30*F or so. Assuming (just for this discussion) that present airflow to a given room is correct, double that flow will be needed upon switchiing to geo.

What really needs to happen is a room by room Manual J load calculation. One input to that software is air temperature rise. The calculation will return CFM required and the ductwork assessed for its ability to move that volume into that room.

What really really needs to happen is a long look at the house as it is now assembled. It may well be that weatherization and insulation can be done at lower cost than extra geo tonnage, yielding a lifetime of operating cost reductions. In addition, if a present 5 ton load is reduced to 3-4, then there is a greater chance of meeting it with little or no ductwork mods.

Beware sixing to meet 100% of design load using geo alone. In a heating-dominated climate, the last ton of capacity, needed just a few hours per year, is nearly always best met using aux strip heaters.

I fully agree with Curt, if you want to do something right, do it once and with an investment as big as this geothermal system you dont' want to save a few dollars that will end up costing you much more in the long run. If you can seal the house better or insulate better start with that to lower your heat load that will reduce the ductwork size needed so that you may not have to modify it. Did either contractor measure all your windows, doors, check insulation values etc and perform a Manual J heat load?

I went through the same decision making process when we just did our system.  The installer who wanted to replace and reconfigure my duct system seemed to be the more knowledgeable of the 2, in our case.  The other installer told me what I wanted to hear...we can use your ducts as is.  The first installer, which we chose, gave me an estimate both ways, but strongly recommended the additional duct work. Rather than seeing it as a chance for him to up-sell the job, it really was just another example of the attention to detail he put into all aspects of the system.  I followed his recommendations and am glad I did.  It would have been a shame to spend the money on the new system, and not have it work as efficiently and quietly as it could have cause I was trying to save money on the ducts.

Yes... one of the contractors gave me a printout of a heat load. My home is ten years old and I had it insulated very well. R 50 in the ceilings and probably over an R20 in walls. Most of my heat loss I was told comes from the many windows in the house which were some of the best on the market at the time.

You really don't know that to any degree of certainty unless the load calculation included results of a blower door test. Conventional fill or batt insulation merely filters air as it leaks past...in fact, a tell-tale sign of air leaking up into an unvented attic is dirty insulation.

At just 10 years old, the house should be fairly tight, but I'd want to know for sure before spending big bucks on 5T worth of geo.

Why not tell us the results of the loss/gain calc.