DIY Digging trenches for Geothermal

3Ts · Nov 26, 2018

I did manual J myself so I know calculations are right.

How do I find someone to do manual J? The installer of our system couldn't figure it out. He only went by "rule of thumb" then after telling me he was going to put in 3 ton AC and 60K BTU heater, he put in 4 ton AC and 80K BTU heater. I think there is to much - the AC ran for 8 minutes and off for about 24 in 107* summer temps, don't know about winter yet, we've not gotten down to our coldest temps yet. Seems to me the ideal operation is that they would run most of the day in the hottest/coldest temperatures. (I've talked to all 3 of the local HVAC contractors, I'll have to go out about 100 miles to get any others)

Is there someplace I can send the specs and get a report? I've done the basic box thermal transfers ignoring the floor and came up with about 30,000 for AC and about 40K for heating.

Diggin It · Nov 26, 2018

3Ts said:
Seems to me the ideal operation is that they would run most of the day in the hottest/coldest temperatures.

You WANT to be burning energy all day and night? I want the furnace and AC OFF as much as possible so they're not costing me money. Come on, do the deed and shut off. Less noise too. I hate noise.

Hickorypond · Nov 26, 2018

Most contractors don't do a manual J, It will affect you a/c from dehumidifying ,short cycle,to large installed usually. On Geo they go too small for heat and put electric resistive to sell you a smaller (cheaper) unit. There are some website calculators, try HVAC Load Calculation - Maunualj - Whole House Loadcalc. Stay away from any unit with a vfd, you'll thank me later. A 2 speed compressor will probably be 2/3 at 1st stage. If you're south of Dallas you shouldn't have to over size to cover heat. I wouldn't trust a contractor on duct size either. Do it yourself ,even if you have it installed. For some reason no one likes to do the math on anything. You can put fudge factor in after calculation.

LD1 · Nov 26, 2018

Yea, that's another gripe I have with hvac contractors in this area....they like to undersize the units. And rely on backup heat in the winter. It kinda defeats the purpose of installing Geo and going "green" and all. Then claim it has to do with dehumidifying the house, and if the ac doesn't run long enough it won't dehumidify and it won't "feel" as comfortable.

Don't buy into that bs either.

Wanting to keep a home 70 when it is 95 outside....that's a 25 degree temp change.

Wanting to keep it 70 when it's 20 outside is a 50 degree Delta. Takes twice as many btus.

So a unit sized for ac....quickly becomes too small once temps drop below 40 in my area.

2-stage helps solve this issue too.

Gofast · Nov 27, 2018

Hickorypond said:
I'll take a picture of the rake & baler tomorrow, may start a new thread under Massey. Don't want to upset the real hay guys.

I work at a large HVAC R&D facility, I bought a Miami Heat Pump for 1/3 of their unit price and mine is built better. Dealer mark-up on unit is 2x minimum. And every time the government subsidizes the price goes up that amount. I paid $6000 for everything, including 2 stage unit,desuperheater,pumps ,pipe,buffer tank and a new water heater plus got 30% tax credit and $1200 from electric utility so $3000,same set up is $30,000 in my area. I did manual J myself so I know calculations are right.

Sweet deal. I wish I could get those prices. My power company gives $400 rebate buy only in you use their preferred contractor. DIY install you get nothing.
At least state and fed your can still get the tax credits with a DIY install.

LD1 · Nov 27, 2018

Hickorypond said:
I work at a large HVAC R&D facility, I bought a Miami Heat Pump for 1/3 of their unit price and mine is built better. Dealer mark-up on unit is 2x minimum. And every time the government subsidizes the price goes up that amount. I paid $6000 for everything, including 2 stage unit,desuperheater,pumps ,pipe,buffer tank and a new water heater plus got 30% tax credit and $1200 from electric utility so $3000,same set up is $30,000 in my area. I did manual J myself so I know calculations are right.

Maybe you answered already....but how many ton is that 2-stage?

Your prices seem about inline with what I remember paying before paying the ductwork contractor.

Did you already have ductwork? or doing that yourself?

We got a $1000 credit for the Geo from the electric company too, and another $400 credit from them for the waterheater I bought to set up a buffer tank. Are you going buffer tank route?

Gofast · Nov 27, 2018

@LD1 sorry to add noise did not read close enough and thought you were asking me that question.

The Geo unit is a 3 ton. I had forced air natural gas heat 100,000 BTU condensing and a 4-ton AC outside unit. It was oversized.
My ductwork goes in one end of NG unit out the other. The Geo unit will be a T install so ductwork will need to be added on both sides of it.

The quote 500-600 was to take away on old stuff and connect the geo unit to the ductwork. I am going to get a second quote. This is all in a crawl space it is about 3 of working space. I will do all the wiring connecting up Geo unit.

I had installed DIY mini splits about 5 years ago. 9k units in 3 bedrooms 30 SEER and 18k in living space duel head unit 21 SEER. I put these in to heat with solar power. We have 3.75 ton mini splits.
We have only used our natural gas heat a couple times in the last 5 years. The mini splits only work down to 5 degrees but it does not usually get that cold here. We have not used the 4ton AC in 5 years.
I will keep the mini splits as backup.

We have a Tankless High Efficiency Condensing Water Heater (Takagi T-H3-DV) DIY install that is 98% efficient.
I did get the hot water option and have been think about getting a used or scratch and dent 50-gallon water heater for a nonpowered buffer tank to feed the tankless heater. Maybe build an insulated box around it.
I might wait till summer to do the hot water part. Our natural gas bill is about $20 month so not much savings there.

Hickorypond · Nov 28, 2018

I put a 4 ton unit in ,sized for 0 degree on heat side,2 1/2 on first stage which is close enough for cooling. Had existing duct but not sized right for heat pump,so I replaced most of it. Air flow across coil is a big deal with refrigeration, gas heat doesn't care. I'm not a fan of flex duct unless its in attic laying on joist with insulation helping to support it. I put 2 water heaters in ,one is for buffer only.Since my loops are sunk in my pond I used a lower circulated water temp of 39 degrees,water is most dense at that temp and sinks.Ground temps will be 50+. A 3/4" pipe is going to come up with a loop a ton,The length depends on where you put it.
This is my 3rd winter with this unit and still happy to have propane tank gone.

Gofast · Dec 1, 2018

I met with a guy that has a 13-ton excavator 3 bucket. Weather permitting, he is coming tomorrow to dig two trenches 275 long 3 wide 6 deep I am going to keep the trenches about 25' apart.

I am going to dig between our house and the horse fence about 25 with my tractor. I will run the pipe and back fill those very big trenches with my tractor. This helped to keep the cost down. This will be a big job on its own.
I am adding LED light bar to help get this done.

I checked rentals buy the time I had the equipment delivered it really was not much different that paying this guy to do it. He is doing it for 1,000-1,100 seemed like a good deal my other quote was 2,100.

The tax credit cover digging so that will help.

My Geo equipment and all the piping shipped it should be here Monday.