[stevehull]

First, a 5 ton system in Portland would supply a HUGE house. Or if it is a smaller house, then it must have several windows open all winter long. A 60,000 BTU/hr system is massive for your area.

Tree roots are simply not a problem - be they fruit trees or anything else. The underground plastic pipe is of small diameter, is flexible and has a very strong construction. And your area is wet enough that drying out the sol via roots is simply not an issue.

Your soil type is important and especially the soil type 5-8 feet down. In Vermont, it is solid granite, so GT heat pumps are horribly expensive to put in. If it is sandy/glacial till (I suspect so), then you have no problems.

You are EXACTLY correct that you could do this yourself. Ingrims water and air has several GT heat pumps and you can get someone to dig trenches for you. Or go with vertical loops.

Another alternative is to hire someone (AC?) to supervise the installation and help out. Or barter for services - I love to do that!. All viable options.

Do you have a prior season's fuel use (electricity, propane, fuel oil, natural gas)? If so, then you have the exact number of heating units already known. This is called performance data and can be quickly used to size a system.

Performance data is actually far better than the infamous "Manual J". Performance data takes into account all the real world issues that the spreadsheet cannot imagine. Find the coldest recent winter and look up the total number of heating units for that winter (kWrs, gallons of propane or fuel oil, cf of natural gas, etc) that the house used. Most utilities keep this on file.

Each of these fuels has a heat content per unit and your heat system has an efficiency. There are calculation spreadsheets on the internet that will quickly convert the units of fuel and efficiency to a season's worth of heat.

Remember that you need several hundred feet of horizontal pipe per ton - so plan for a lot of trenching! And don't forget the lines coming into/out of house to horizontal ground loops. The specific number will be determined by your soil type, trench depth and obviously system capacity.

Then you size your system accordingly. Not hard.

Let us know if you need any help with the above.

Steve