I am constructing a new house in central NJ and have contacted 3 HVAC geothermal contractors for sizing and bids. The estimates for trench & pipe length I have gotten are so varied that I am having a real quandary in deciding what to do. I am a person who does not know anything about HVAC system. The spec for the house is given below
- 3800 sqft conditioned space on two level
- Full basement but not conditioned
- House facing NNE
- All windows double pane, low-e, argon filled (most windows on NNE and EES side)
- Insulation – blown closed cell cellulose insulation (do not know the R value, but I am sure they are very high compared to, for example batt)
- Soil type – damp heavy
Estimates from the three contractors I had spoken to are as follows
- Contractor #1 recommends a 5 Ton systems with about 125’ of trench per ton with slinky loop, with 36” diameter and 10” pitch – he was just speaking from experience.
- Contractor #2 recommends a 7 Ton system with about 125’ of trench per ton with slinky loop, with 36” diameter and 10” pitch – he was just speaking from experience.
- Contractor #3 actually showed me a manual J he did and he says he used Wrightsoft hvac software to come up with loop design. This person has given me most information, but his estimates are enormously higher than others. His load calculations were as follows
o Heating load = 64675 BTUH / Cooling load = 42079 BTUH (when it is 2*F outside)
o Trench: 14 trenches of 182’ each for a total of 2544’ of trenches
o Total pipe at 6’ deep is about 32453’. Pipe diameter in the ground loop is 0.75”. 10” pitch and 14 parallel loops
o Equipment: FHP Aquarius EC072-1HZ/VT
o Supplemental heat: 3201 BTUH (0.94 KW)
o EWT – heating: Design 39*F / Actual 39*F. cooling: Design 87*F / Actual 72*F
As you see the estimates are quite disparate and I not knowing much do not have any idea as to what is a good estimate. But after reading through various geothermal and hvac web sites, it seems that about 100’ – 125’ of trench per ton seems more in line with most what is written and can be found over the web.
If required I could send out the blue prints or any other supporting documents I have. Please, any help is very much appreciated and thank you all in advance.