My wife and I plan to replace our inefficient oil furnaces (2) with a geothermal heat pump system using horizontal loops in our 3/4 acre back yard. We are quite impressed with the use friends of ours here in northern Maine have had for up to 20 years!

The local distributor told us that the most efficient system was to install 250 feet of piping per ton in trenches six feet deep (frost goes deep here) and four to six feet in width. We were told that we should have each loop go up and back in one trench, keeping the piping at least two feet apart. Then, each trench should be at least 12 feet apart...

Researching online, it appears that the slinky system would be an effective alternative, as would a multipipe system in the trenches. It also seems like the system would be more efficient by having pipes start at one end of the trench and end at the the other end (back at the house) instead of going up and back in the same trench. Is this right?

If we went with multiple pipes in the trenches, how many pipes could we put in each trench and how far apart should pipes be from each other to be the most effective?

The only licensed installer in the area quoted $82,000 to install a system to heat our 3800 square foot 135 year old home! To be fair, he suggested putting in four - three ton units so that we could adjust temperatures in different parts of the building. I think we can get by with just one thermostat... The local installer also is very busy so it looks like we will have to do this ourselves instead. For that reason, I want to avoid having to join pipes anywhere but the manifold.

Our house is moderately well insulated, for an old house... We used 1900 gallons of fuel oil to heat the place last year. Does it sound like we could get by with just one - six ton unit?

Thank you in advance for any and all advice and encouragement!

Fred

Off the cuff, I've no idea. What was the btu requirement per zone? What brand is your guy selling?
Look at competitive manufacturer websites for other local dealers (can't believe Maine has only one dealer). We have installs in 3 states.

There are lots of ways of putting pipe in the ground and they all work well.  They all have their advantages.  A slinky systems uses more pipe per foot of trench (8')  than a two pipe system, which uses to 2' of pipe per foot of trench.   With a Slinky system you use a lot more pipe, but do less digging.  I have a slinky system in my house.  It works great.  I used 1250' of pipe per ton.  I have 6000' of pipe in 500' of trench.

Digging a 2' wide by 250' long trench and running  one 500' length of pipe out and back in the same trench will give you a great system.

Digging a 6' wide  by 250' long trench and running two lengths of pipe out and back in the same trench will give you a great system.


The recommendation on trench spacing is 10'   We have done less and not had problems.   

It would take a huge excavator to dig a trench 6' wide. 

If I were doing this,  I would dig a 2' trench by 250' and lay one pipe out and back.

This would enable you to bring all of the ends into your house for manifolding.

There is no way for us to tell you what size heat pump would work for your house with the limited info you have given.

You need someone to do a Manual J heat load calculation in order to properly size the heat pump.

If you have two furnaces now,  you would probably need two heat pumps.

What kind of pipe system do your neighbors have?

Hope this helps

Thanks for such quick responses! To respond to your comments/questions:

We have two 65000 btu oil furnaces now. Each furnace serves one unit of the duplex. Neither run very often or very long so it seems like we don't need as much btu output as they give...

The friends of ours who have had geothermal for 20 years plus each have open loops with a drilled well for input and a pond for output. There is another one which uses a horizontal closed loop system with 250 foot long trenches 12 feet apart with a 500 foot pipe out and back in each trench. Their system has only been installed for one year. Each of these are using the Nordic heat pump, made in New Brunswick, Canada. (We live only three miles from the border of New Brunswick).

We don't have the room or drainage necessary to do an open loop with a pond. We considered putting in a two well system but the Maine Department of Environmental Protection now requires a $600 test for any water that would be discharged back into the aquifer. Any pollutants found, even if they were in the water drawn from the well) would have to be removed before putting the water back into the ground... (Seems overkill to me...)

We have been dealing with just the local dealer because the next closest dealer we know of is 200 miles south of us and they are so busy there they won't even consider coming this far north... There is a new distributor/dealer for Climate Master heat pumps in the area, but he has yet to ever install a system. Strange that it would make me nervous about using him if I am considering doing this myself since I have never done it before either! ;-)

I was hoping to be able to stick with 500 foot long lengths of pipe so that I would not have to try to weld them...

Can anyone recommend a website that compares the efficiency and cost of different brands and models of geothermal heat pumps?

Thanks again for your advice and encouragement!

Fred

Again a heat load answers sizing/loop length questions. Nordic must have more than 1 dealer in your area. They also make a DX system. contrary to my thoughts that waiting generally costs you more, I think that the lack of second opinions might be more expensive in this case (there's the exception for devil's advocates).
As far as first time installations, we all had one (I shudder to mention what year that was for me). It is likely not their first installation even if it's their first geo installation. Let's have feedback from other customers and inquire about supplier support as well. Climatemaster will not sell to everyone with a shingle, there is at least cursory training. Don't be afraid to ask for local rep reassurance as well.
My guess is we are seeing inflated prices in your area due to lack of dealers.
If the figure they gave you turns out to be accurate and you don't have alternatives then maybe you want to do what Engineer did and start your own operation. I'm in New Brunswick every other spring; at 40K a system, I may want to up my frequency. For what I percieve the inflated mark-up to be, you could fly in an advisor/installer.
J

As far as efficiency and cost of different brands, geothermal heat pumps are 300-500% efficient compared to fuel oil at 80-90% efficient.

Each brand of geothermal can have a different efficiency with the same model, depending on ground loop type. You're talking about closed loop. Most likely, a DX system will be a higher efficiency than a water loop system on a closed loop. Also, DX should be a lower installed price than a water source system. However, if you don't have a local installer for DX, you're better off with something else, as long as it's geo.

For a horizontal loop field, and EarthLinked DX system would perform at about 420-450% efficiency (COP=4.2 - 4.5). I think Nordic's DX system would be around the 3.8 - 4.2 COP. Others here can tell you what a closed loop water system typically is. Basically, though, it doesn't really matter what brand, (unless referring to Hydra Delta--see related threads here on the forum), as long as it's installed, sized, and designed correctly.

On your price, it seems like a decent price for 4 separate systems. I don't think you'll need 4, though. Like Dewayne said, with 2 furnaces you should be able to do it with 2 geo systems. That should cut the cost significantly.