Kentucky What register temps should I expect?

Discussion in 'Maintenance and Troubleshooting' started by Jmac55, Jan 9, 2015.

  1. Jmac55

    Jmac55 Member

    New to forum. Little knowledge of technical specs etc. Am from London, England originally so can just about change a light-bulb!

    I have had a geothermal vertical system installed last year and here are some details I know.

    Piping size entering/ leaving home 1.25” Piping size and length in ground .75” approximately, 600’ (plus another 125' added after installation!)

    10kw auxiliary heat strips

    Comfort-aire Model HTV036A1C01ARK

    Hope someone can help with some pretty straightforward questions.

    Last year we has a brutal winter here for northern Kentucky! Temps got to 0.F and weeks below zero daytime. Set thermostat to 72.F and just let system do it's thing, as advised by installers. No set-back etc.

    Electric bills per month $450 (so about $300-325 on geo I estimate). Realized that not really saving much over our old (old) oil furnace, heating wise. (Air conditioning worked fine btw)

    Problem: Auxiliary heat comes on nearly all the time when outside temps drop below 32.F

    This winter started temperature reading at nearest register to unit in basement, (which is about 5' away) with Aux turned off to see how geo was operating.

    On a 40.F outside temperature it will put out 92.F Max.

    When outside temps drop below zero and lower, the register temps slowly drop to about 79.F. (which, understandably, cannot maintain acceptable heat in older home, hence aux heat coming on)

    I was under the impression that the output of heat from the unit should remain constant since geo isn't affected by outside temps. (like an air source hp)

    Am I wrong?

    Are these register temps within acceptable parameters (if there are any)?

  2. Jmac55

    Jmac55 Member

    I should add...

    The system is 3 ton

    1800 sq' house built in 70's.

    Unit is in (below ground) basement.

    Pipes enter house 3' below grade.
  3. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    You should see around 20F in temperature bump. You can look up your units' specs.

    Is your ducting in uninsulated spaces?
  4. dgbair

    dgbair Just a hobby Forum Leader

    Where are you measuring the temperature? At the register or in the main duct right off the unit?
  5. Jmac55

    Jmac55 Member

    OK not familiar with terminology and am learning about geo. so don't want to appear too dense.

    You should see around 20F in temperature bump.

    I'm guessing that means I should see a rise in temperature? Compared to what?

    You can look up your units' specs.

    I have the installers handbook, but not sure what spec I should be looking for.

    Is your ducting in uninsulated spaces?

    Nearly all of it is insulated space, although some duct-work runs behind drywall on an outside wall to the top of the house, so hopefully was insulated appropriately when the house was built.

    However, my problem (as I perceive it) is that I'm taking temperatures from the nearest register to the unit in an insulated, heated basement and I am trying to determine why geothermal output temps (with auxiliary heat turned off) would drop 15 degrees after a few hours of running on below freezing days.

    Above freezing temperatures outside, it will put out a constant 92.F....but when the temperature outside drops below freezing the unit's output drops significantly to 79.F and dropping!

    I guess I need to know 'Why?' since I understood that geothermal output should not be affected by outside temperatures.
  6. Jmac55

    Jmac55 Member

    The unit is the (heated) basement and there is a register within 5' and I'm taking a reading from there.(I have taken readings directly from inside the unit... but the difference is probably less than 1.F)

    On a below freezing day, I have run the unit and turned off the auxilliary back-up to see how the geo only performs, and that temperature reading drops about 15.F (and falling) after a few hours.

    I understood (maybe incorrectly) that the output from the geo should be fairly constant despite outside weather conditions.
  7. dgbair

    dgbair Just a hobby Forum Leader

    It would be best if you could take temp reading right at the unit. You need to compare cold air return temp to the supply air temp. ie EAT, LAT The delta between the two should be around that 20F that Chris talked about. Look around for a small hole in the duct where you could insert the temperature probe. We really need to understand if the EAT and LAT are both falling or just the LAT.

    IMO - Two tools every geo tinker should have: (but if you can't change a light bulb, maybe these are not for you :D)
    1- Cooper-Atkins DFP450W-0-8 Digital Pocket Test (or something like it)
    2- A pressure gauge hooked up to a needle probe (a athletic ball inflation needle works well)

    With these two tools, you can at least get the initial data needed for problem debug.
  8. Jmac55

    Jmac55 Member

    Ahh...thanks! Think I understand now.

    Will try to obtain tools and figure out delta.
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    Hello and welcome.

    I love London. I am sorry they do not teach how to change a light bulb in Primary.

    Get the tools dgbair recommends and you will become an expert. One of my supply houses here in Ohio caries a petes port tool that is designed to hook uo to a 1/4" mpt gauge. Wolff Bros. Supply Medina OH.

    330.725.3451, troll to HVAC.

  10. Jmac55

    Jmac55 Member

    Thanks Mark...they did teach us how to change a light-bulb, but they're bayonet type in the UK and yours are a screw thread!

    I'm getting the impression that there is a problem with the system.

    Since I'm still under warranty, I'd like the company that installed it to solve it to be honest. I'd love to become more of an expert, but my immediate need is to point out to them that something is wrong.

    To this end I was trying to determine if it is normal that the geothermal heat output at the source should drop so dramatically when it gets below freezing outside or whether that output should remain constant (as I was led to believe) since the source for the heat should remain constant.

    As much as I've read here and elsewhere, there's a possibility that my boreholes are not operating efficiently in transferring heat to my pipes (for reasons unknown...but the installers don't believe in using grout!) and the pipes (and the ground around them) are getting colder and colder as the cold fluid recirculates.

    I have taken surface reading from my input pipe (37.F) and my output pipe (31.F) yesterday. I would have imagined that my input should have been warmer...but maybe I'm wrong.

    Anyway, I will try to obtain the tools in the next few weeks and make some determination for myself.

    Thanks for your advice.
  11. pfer10

    pfer10 Member

    Jmac just to give you an idea of where your numbers fall I can give you some of my system which is similar. I am in a 2400 sqft 1/2 built in the 50s above a 1200 ft basement (not in the 2400 #) where the geo is and 1/2 of it is a newer edition built in 80s. Just north of you in Indiana and the highest bill last year was $245 in Feb (probably should get you my kWhs used). I minimized aux heat use last year before the cold hit by adjusting where it comes in at at. I keep the thermostat set at 68 with a 1.5 drop. I now have my aux heat come in if it drops 2 degrees. My 2004 geo unit is 3.5 tons and it can keep up with my house to about 5-10 degrees outside at 68 set point although the house isn't balanced very good so one end hovers around 65. It then looses temp below that. Last night we reached -2 and I had almost an hour of aux heat to keep it at 66 at the thermostat. I benefit from a great room on the second story of the edition that has a south facing 9' x 5' window so on a sunny day like today the thermostat might read 67.5 but the room I spend the most time in is 75 when outside temp is still at 14.

    I have outfitted the house with temps at various places and the temps on the geo unit. My temp across the return and supply of the geo is pretty much always 20 - 21 degrees different. Exiting air will be 87 and entering air will be 66 this morning before sun got very high. I have one temp at the end of a long duct run to the edition and it is usually 3 - 4 degrees below the supply at the geo. The duct is un-insulated and runs in the 58-59 degree basement for 12 ft and exits 18 ft (all conditioned space) after that where I usually see a 3 - 4 degree drop from the geo supply temp.

    You really need to get flow of the loop to help the guys diagnose what is wrong and that is why they want you to get the pressure gauges and ports so they can look up the data for you. Looking at specs of a similar 3 ton unit your heat absorbed from the loop should be about 20K. To calculate that you need your temp difference in the loop and the flow. Heat absorbed = (difference in temp) x gallons per minute x 60 x 8.35. Just looking at some numbers if your surface temps are right and the unit was doing 20k heat absorbed from the water your flow would be be about 6.7 gpm.

    They suggest 3 gpm per ton so you should be at ~9 gpm. But I am just taking a guess at heat absorbed and your flow. What you might do without the additional tools is watch your difference across your entering water temp and exiting water temp. Give it plenty of run time to let everything settle and since you are taking temps on the surface try to insulate the probe with some extra pipe wrap if you got it so you aren't picking up the air temp. If that varies by a bunch either your unit isn't running right or you flow is going up and down. I would think your flow would be steady unless you can hear a noise difference in your circulation pump. If that temperature stays pretty steady across the loop then your unit is absorbing consistent heat if the flow is steady.

    Try to monitor that difference and your difference across the supply and return at the geo and that will tell you a lot about what the unit is doing but you still need to get the pressures to get the flow so the guys can nail it down. If your supply at the geo stays pretty consistent and your duct temp really is that low at the vent with a big drop in outside temps then you have duct work problems. Just wondering is the duct work from a previous heating / cooling unit or is it new with the geo?
  12. Jmac55

    Jmac55 Member


    That is useful information to compare to my unit.

    I have to say I'm reasonably happy with geo...except when the temperatures plummet way below freezing for days on end. It does seem to tax it and over a time period the geo temps begin to drop and the (electric) auxiliary comes on longer and longer and that wipes out much of the savings I might have made.

    Last year near the end of the very (very!) cold spell, the auxiliary never shut off and I called the installers and they found that the pipes in the house (exiting the unit I think) were freezing. You could hear the ice in the pump. They flushed it out and 'rested' it, but at the beginning of this season, the same problems arose and they finally drilled another hole which seemed to have solved that particular problem...although the original pump failed after that and they replaced it with a better one (I hope)!

    It seems to be a very delicately balanced piece of science and to get the best efficiency from it is more complicated than I imagined.

    In the last 12 months I have boxed in and insulated some duct-work (that had no insulation) behind drywall in the garage, replaced old windows and insulated duct-work in the basement and it has improved...but then this year is no-where near as cold as last year.

    I am determined to get it working the best it can, for my part, and to that end I will buy the tools to do that, but I need the co-operation of the installers for sure if it is a major problem.

    I should add that it is running through old duct-work installed when the house was built.

    We originally had an old oil furnace and when that packed up and the air conditioner also failed within six months, since we have to natural gas here, it was either an air heat-pump with auxiliary electric or geo. with auxiliary electric.

    The selling point for geo was that it isn't affected by outside temperature regarding output of heat, but that doesn't seem to be the case.

    Thanks again for the info, it is very much appreciated.
  13. Jmac55

    Jmac55 Member

    ...since we have to natural gas here...

    ...since we have NO natural gas here...
  14. Jmac55

    Jmac55 Member

    I have to let you all know that my problem is, I hope, resolved by reading on this forum (and finally understanding) that the return temps taken at the unit should be within 15-20 degrees of output, and why it's significant that the reading is taken there! I now understand that the unit is heating air from the house that has been previously warmed and is recirculating it.

    My geothermal was installed in an unheated basement (I had closed down the registers several years ago when I had oil heat... an old door leading to the garage let more air out than it kept in.

    No problems there...but for the fact that the return duct-work from the house was open (i.e. not enclosed) after it entered the basement! The result was that the geothermal was drawing in freezing cold air from the basement and trying to heat that! It was working four times harder than it should have been!

    I sealed the door to the garage, opened the registers to warm up the basement and sealed the open return duct.

    Temperatures are now maintained and the auxiliary rarely comes on at all.

    It was a straightforward problem in the end...but I guess that the installers should have verified that the old duct-work was fit for purpose. They came several times to troubleshoot the problem, but I don't recall them taking return temps at the unit which would have shown how cold the incoming air was. They kept looking at the unit they had installed and didn't look at other potential problems.

    Anyway, reading on this forum finally got me to look at return temps which led me to the open duct hidden behind the plumbing and suddenly the light-bulb went thanks for the help everyone.

    I have ordered some tools and instruments that will help me diagnose any future problems, if they arise, and I'll be able to give better numbers in future.
  15. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Maybe look at closing off the registers in the basement if you are not living down there.
  16. Jmac55

    Jmac55 Member

    Actually, keeping the basement warm (now that I've sealed off the outside door) has helped somewhat since (our also new wooden floors replacing carpet) above is not as chilly. At least the warm air is rising!

    I'm realizing that geo isn't at all like fossil fuel heat and has a lot more to do with good balance and slow and steady wins the day.

    My old oil heating just seemed to pump out hot air...switched cold...then pumped out hot air...switched cold, and repeat all day! It was very inefficient and we constantly went from feeling cold to feeling hot! Not at all comfortable.

    Now that my geo is working more efficiently, it just ticks over all day and keeps a steady temperature, hopefully efficiently and economically.

    Thanks again for the good advice.
  17. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    sure glad to hear that!!!
  18. Jmac55

    Jmac55 Member

    Just made tool to take readings from Pete's port.

    Water in 75 psi
    Water out 70 psi

    Here is pix of Pete's port where I took readings. I can't see any others so hoping this correct points to take readings.

    Photo attached to show location on Comfort-aire Model HTV036A1C01ARK

    Had bought a cheap insert thermometer, but it stopped working as soon as I got it home so will invest in better tool.

    Attached Files:

  19. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Cooper Atkins makes some robust and accurate narrow tip thermometers most excellent for Pete ports.
  20. Jmac55

    Jmac55 Member

    I have already ordered Fieldpiece SPK2 Folding Pocket In-Duct Thermometer which looks the business!

    But thanks for tip.

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