I'm looking to have roughly 2 400-ft wells drilled for an install with a 4-ton Waterfurnace Series 5 (049 model). (Another possibility is 3 266-ft wells.)

I've had some installers propose using 1" pipe and some propose using 1 1/4" pipe (and frankly, I'm not sure if something else would be better anyway).

Ignoring those specific sizes, just so I understand, what effect does having a larger pipe diameter have on the project? Specifically, does it always increase or decrease efficiency? Are there concerns about having a sufficiently powerful pump as pipes get too wide or narrow? Does it affect the expected lifetime of the system? (There has been some discussion of this stuff in these forums before, not everything being said was clear.) Are there any downsides other than price?

Does anyone have a rough idea of how much of a total price difference one would expect between 1" and 1 1/4" pipe, for example (either by foot for total for my project which will have about 1'600 feet of vertical pipe)?

Does anyone have thoughts on what would make the most sense for my 2-loop vertical system in Maryland? Would something like 1 1/2" or even 2" pipe be better? (In the end, I'm most interested in having a very efficient, long lasting system, even if it costs more now, and potentially even if the payback period is horrible.)

On a related note, does anyone have any comments about the depth of the wells (because different contractors have also given different numbers here, most of them smaller than the 2 400-ft wells I mention above, but I want to error on the side of more medium to exchange heat with rather than less)? Is there a difference between 2 400-ft wells or 3 266-ft wells, for example?

I assume that as you increase the length of the pipe in the ground, you need to increase the size of the unit, specifically the pump, in the home to pump the fluid through the increased length of pipe. ...but this makes sense for the 4 ton 2-speed Waterfurnace series 5 (049)?

Thoughts on any one of these questions would be very much appreciated. (Too many opinions from too many different contractors. The one I'm going with is also tired of me asking questions, but it's a $30,000 project (20 after tax incentives), which is the most I've ever paid for anything other than a house, so I want to make sure it's as good as it can be, and importantly, I want to understand and know about the system in place.)

Thanks!

generally 1.25" pipe is used on 400' deep loops and 1" pipe is used on 300' or less loops. The reason for this is to keep pumping pressure lower.
Price difference would not be much 3* 266= 798 2 * 400 = 800, so both will perform the same unless there ground is more saturated below 300'

1.25" pipe is the largest available for ground loops.

If money is not the primary concern, you should look at a series 7.
Overall pipe length is likely greater than our average in mid MI (we go somewhere around 150'/ton on vertical loops).

In general, 1.25" have about a 5% better performance than 1" vertical pipes due to the larger diameter. However, which is not accounted for is the much higher thermal mass of the water fluid in the pipes, resulting in a much higher thermal inertia.

If your pipe diameter gets too large, you might not have enough turbulent flow in your pipes, reducing the efficiency. For a 4 ton system, you only need 12 gpm. Make sure there is a pressure drop calculation done to reduce your pumping power!

I am with Joe, the length of pipe in the ground might be more than needed, however, I don't know your specific geology. You could fine-tune the design and put the money in an upgrade of the 7-series, you would significantly increase your comfort and efficiency. 5-series is one of the best dual speed heat pumps on the market, but nothing beats the variable speed 7 series.

Thank you for the replies.

All the installers with whom I spoke seemed to think the 5 series made the most sense. One said I really needed a zoned system in my house to take advantage of the 7 series. (I believe he seemed to think that the speed would never drop below the low speed on the series 5, so I wouldn't see any significant benefit if I'm relaying correctly. Would that make sense? Zoning isn't really practical in my house, without completely redoing all the duct work, FYI.)

Is the pressure drop calculation something done to size the pipe or something that is done upon install within the system?

To recap and make sure I'm not missing something, it's not clear that 1" or 1.25" is better (ignoring install cost)? 1.25" may be more efficient but it may not be if the turbulent flow is too low?

(The pipe length is longer than a typical 4 ton here. There was a lot of debate between installing a 4 ton and 5 ton system. Again, I got different numbers from different installers. I opted for the increased pipe length, while discussing with the installer who I'm going with, to have a little more ground with which to exchange heat and ideally increase efficiency, partly because we're between the 4 and 5 ton. Does that make sense?)

Thanks again.

7 series can drop the speed to 21%, it simply provide so much more comfort, and also is more efficient at those lower speeds. While is works great with zones, it works also great without zones. Most of our 7 series installs is without zoning. I would always use 1.25", unless there are very special circumstances, like I can only go down to 100', and I need to put in many boreholes, but do not need much GPM. Pressure drop is done to design the entire loop configuration, to reduce friction loss and reduce pumping power.

Any idea how much the energy/cost savings might be with a 7 series vs. a 5 series for a typical 4-ton, single zone house? Do you know what the rough upfront cost difference is? With both intelligently slow things down with A/C, for example, to reduce humidity? (Personally, I'm not too worried about comfort. I've never really been uncomfortable due to the temperature of my house.) Any expected differences in reliability/longevity?

We measure 22%, List price is $6000 more, which includes the variable speed circulation pump, but your don't need the intellistart soft start kit. We sell it for about $4K more, after tax credits it is $2800 more, since we want the technology out there, and the customers are loving it. Yes, the humidity control can be fine tuned. We put them in for 18 months now, not a single call back on 30 units. Can't say much about 10 years from now.