hi, looking for some rules of thumb for appropriate length of horizontal ground loop, either per ton, or for our 3.5 ton total need (we have two zones, so planning two separate heat pumps (splits)).  Thanks

I recommend getting software such as "Ground Loop Designer".

appreciate that suggestion, but as homeowner looking for something a little more cost effective, looks to be $800.... further thoughts welcome, thanks

thanks.  not a DIYer, i actually have the system already installed, and have a run of 670 feet, and i am fearing it may not be long enough, or rather, trying to determine if that is the flaw, or if there is another flaw.  working to gather in and out temp data, really just want to know rule of thumb, am i close to what i need or did i get hosed.  and if hosed, then my question will be what are options, can i get a vendor to add a vertical loop to a system that is already based on a horizontal set up?

it's not that simple. there are regional expectations of what is satisfactory, but soil, weather, design....so many things impact this.
Perhaps if you could offer some design info.....
j

sandy clay, mid atlantic (maryland) region, 6 to 10 foot depth in trenches.

and not a slinky or coiled loop, but straight black tubing

Thought I responded already (begs the question where'd i submit that one)....
loop pipe diameter, load of the house etc.
I like brevity, but you offer a little too little.
J

My system, in N. Arkansas with 58 degree damp clay is 3.5 tons with two 600' loops on the one ton and four 600' loops on the 2.5 ton. All at 7-8' and has been working for 15 yrs. My water temps have never been lower than 38 but they were higher than normal at the end of this summer at 78 degrees. I only use the heat strips a couple of times a year to burn off the dust.

Posted By arkieoscar on 11 Jan 2011 07:42 PM
I only use the heat strips a couple of times a year to burn off the dust.

Small hijack.  I was just asking about this elsewhere.  How many times per year do you do this?

I love the smell of burnt aux dust in the morning (not really - it stinks!)

I normally do it on warm days in winter, when I can open the house for a couple of hours.
In response to the OP, when the EWT is down at 38 the LWT is usually right around 32. Normally this only occurs for a couple of weeks in Feb. As we get warmer days, the system runs less, allowing water temps to rise. The system is protected (prop. glycol) down to about 15 degrees. It is closed loop and not pressurized.

Those temps sound fine to me.