Hello,

I am trying to install a waterfurnace geo system in my house and I keep getting different recommendations on how deep my well needs to be.  I am in the boston area and am looking to size the unit for a 2K SF house that will hopefully grow to 3K SF in the future (within 5 to 10 years).  We are being told that we need a 5 ton system and a 400' well with 1.25" piping to support the system. 

But when I talk to others:  
   my general contractor who is not involved in my geo system negotiations is working on another project of similar size to mine and they are drilling three wells each approximately 300' and was surprised that our recommendation was so low and suggested I revisit this number with my distributor.
   a well drilling company came out and said all of the projects he has ever done and he has been doing this for many, many years - they use a standard 150' per ton and recommends 2 wells 350' deep.

I've spoken with my distributor and he stands firm with the 400' recommendation.  Can anyone support or refute any of these numbers? 

Thanks in advance.

Heather

Sorry, more detail - we are looking at a closed loop vertical system, not an open standing column.

All geothermal projects must start with a Manual J load calculation. Then run your loads through a geo-design software program. If your HVAC contractor does not find another. 

5-10 years is a long time to have a substantially oversized system

I agree.  One option that I am likely to pursue is drilling the well to the oversized depth and going with a smaller heat exchanger for the time being.  Still, I am trying to verify what depth of well is appropriate for either a 4 ton or 5 ton system.  Do you have any insights? 

80' or 90' per ton versus 150' per ton is a huge variance.

The geo-design program will tell you how many feet of bore hole you will need in total. How you divide it up depends on your site and driller 

In Utah, we average 150' - 200' of bore hole per ton of capacity. This holds true for most parts of the country. But as has been said, your specific job needs to be designed by computation not rule of thumb or averages. You are right to question the design of a single 400 well'. It seems low to me, but not knowing how it was calculated, I can't say.

There is another problem with a single well. You would have to push 15 gpm through 800' of 1.25" pipe which is beyond the capacity of a normal flow center. By splitting the flow between two wells, then a flow center can handle to flow.

Thank you for your responses.  150'-200' per ton is bad news for me.  That would double my drilling costs and makes the costs way too prohibitive.  If I were to pursue geo then the distributor would have done a thorough heat gain/loss analysis.  However, they and everyone else that I've talked to give preliminary numbers so that it's possible to get a sense for costs and get financing in place.

I don't distrust my distributor, as a matter of fact I really like them.  But I am concerned with what seems like a very large disparity between what they are calculating and what the majority of the industry is calculating.  Having said that, I also had other people quote smaller drilling needs (250' for 3 ton system for example).  I'm wondering what could be causing the big difference.  Are there new efficiencies in the Waterfurnace Envision series, or just simply better sizing techniques that makes a difference on how large the well exposures need to be?

Ask them to guarantee that the loop temp will never drop below 30° coming from the loop into the heat pump. This is what your system would need to give you the performance you will expect. If the system is short looped, you can be without heat before the heating season ends. Be very careful.

There are contractors who are confident enough in their loop design who offer just such guarantees.

The efficiency of the heat pump has nothing to do with how much loop you need. It is the speed at which heat can move from the ground into your loop (which is confined to a pretty narrow range) and how much heat you want to put into your house that determines how much pipe you will need.

Ask them for other jobs that they have done using 80' bore hole per ton. See how well those systems perform.

If you do go ahead with this, do NOT use a single well!!! The water will be flowing through the pipe too fast for efficient heat transfer. Most loops are designed with one parallel path per ton. This allows for sufficient residence time of the water in the loop which provides proper heat transfer.

I worry about your distributor. He should know about these criteria.

Good geo designers have access to software which will determine the heat load of your house which dictates how much pipe you need in the ground.

At the very least, you should get lots of references for people that he has done jobs for. Call them, go and see them. There are several red flags here.

Yes, references have been requested and checking on them is the plan. And I'm being told our distributor is using 'industry standards and waterfurnace proprietary sizing software'.

If anyone has recommendations on distributors in the boston area that are respectable, I would really appreciate the leads. It appears that demand is higher than supply in the boston area (although recent events in the financial markets may be changing things a little bit now). I have a hard time getting suppliers to even return my calls, never mind actually come out, review the site and talk in depth. And I understand that costs are higher in the boston area but almost 20 years payback period even with a projected 60% savings in energy cost is simply too high and makes going with geo unattainable and even financially irresponsible - there are other alternatives that offer a better total cost of ownership.

20 year pay back ??? I wouldn't do it either. Let us know how it goes.

When you say distributor, I suspect you mean contractor, unless you are a contractor yourself. I think you need to poll other contractors.
J

You should check with an EarthLinked system. It would be 100' per ton, and possibly smaller drilling equipment is available for it.

Call Mel Hensch. He's the EarthLinked sales rep for your area and will know what dealers you should contact.

Mel Hensch
[email protected]
508-328-4735 phone

  Ask to see the calculations that have been done for your system.

There is no way that "waterfurnace proprietary sizing software" would design a single bore hole for a 5 ton system.

I have used that software,  I know how it works!

Thank you for the lead, I will definately call him. 

If anyone else has other recommendations or thoughts, please post and I will follow up.  Thank you!

Same as always, more estimates and contact their references.
Good Luck
J