Hi Everyone! I recently got quoted a 10 ton GSHP for my large home (they didn't do any calculations, rule of thumb) but after I crunched the numbers I feel it would be far oversized. From what I have gathered reading this most excellent forum oversizing a heat pump is not a good idea, especially if you end up with a desuperheater for DHW. The yard out front is barely large enough for a horizontal loop for the 10 ton. It can be done if we just pit the whole yard, but there is more than enough space for a smaller GSHP. I have been tracking my utility bills on a spreadsheet for the past few years and used the actual GJ of natural gas used with the Heating degree days calculation to determine the heating load of my home. I have one mid efficiency furnace for the main home, one gravity dump low eff furnace for the basement, one overhead heater in the garage, and one 50 gal hot water tank also on natural gas. When I did the calculations I assumed 80% overall efficiency which is in my mind probably giving the units too much credit. Changing the efficiency value even 10% one way or the other has big effects and i did not want to be low on my estimated heat load. I have everything in an excel file and it has about 36 months of usage history. Sheet 2 shows avg BTUH for every month and the calculated heat load for every month. The largest usage months here are december, january, and february by far. The heat load calcs are actually quite skewed for the summer months since there are almost no heating degree days but the hot water tank still runs and it causes the calculation to be weighted unevenly and show too high a load for the home. I found it really interesting. I was also blown away by how much my actual gas usage dropped after the summer of 2018. That summer I spray foamed the basement and changed some more windows and the usage is down like 40%! I did not think it was that much because I was watching my utility bill costs and it didn't seem to change year to year but the insulating has definitely made a huge difference now that I graph these values. So for the heat load we should be looking at just 2018/2019 winter and 2019/2020 winter. OK OK, so my question is: Does it sound reasonable from the usage data that I should use a 5 or 6 ton unit? I am leaning toward 5 ton from the data but wanted to ask those who have real experience if it's wise to size for 100% of the load, or 90%, or 110% etc. Just wanted to discuss the heat load here... I will reserve my ground loop questions for later.