Good morning, I wanted to post about concerns with my new geothermal installation and get any thoughts if possible. I recently (November 15th, 2018) installed a new geothermal system. When the temperature is below 15 degrees, the geothermal cannot keep up, with the AUX 64,000 btu electric back up heater kicking on. I was freaking out after the first month, so I disabled 1 of the 2 electric backup, so I'm now only using 32,000 btu of back up heat. During the night the last few days with a temp of 10 degrees outside, the AUX runs all night and the house does not maintain temperature, dropping down to 60 in 1 of the zones. In the month of December, my electric bill skyrocketed to $900, and I used over 8,000 kwH versus 2400 kwHs the previous year. I was previously heating with Propane, costing me $750/month on an 11 month even payment plan, so clearly in the winter months I was blowing through $1500 or even more a month in Propane. I had 2 different contractors perform a manual J, and 1 sized the unit at 5 tons, the other at 5.75 tons. The house specifications: Cape Cod style with 4,284 sq ft above ground, and 3,200 below grade, walk out basement with poured concrete walls around 75% of the basement. The system installed: 6 ton, 2 stage Waterfurnace Series 5, horizontal loop with 3,000 ft of 3/4" pipe in 6 circuits. 4 zones, 2 upstairs, 2 main floor. In fairness to the contractor, he did tell me I needed to insulate the basement for this system to function optimally during the coldest days. Are there any things I should be checking to ensure proper function? Could the basement walls be causing the level of heat loss I'm experiencing? I appreciate any insight. Regards, Nathan
For what it's worth (I'm no expert), I live in Massachusetts and my 3468sqft house (basement contributes about 1000 sqft to that) was sized by Manual J for 56k BTU (basement contributes about 6k BTU towards that total load), which means about a 5 to 6 ton system. My house was built 50 years ago... R11 in the walls, original single pane windows plus storm windows, and attic is spray foamed to R38. Comparing my house to yours, it surprises me that we are both sized for the same tonnage, unless you have a really well insulated house with new windows I suppose. Best of luck with this arctic blast coming on tonight and tomorrow.
Brad, Thank you for the reply. My heating load was calculated at 76,976 BTU, or 6.5 tons. The second company gave a range from 78,000 BTU to 88,000 BTU, or 6.5 to 7.3 tons. Is a 6 ton unit versus a load of 6.5 or 7 tons going to be something where I just need to better insulate versus some sort of system change? Regards, Nathan
I am not an installer like a lot of the other guys on this board, so if they chime in it will be more helpful, but it sounds to me like you're undersized. If you look up your model number here, you can compare your Manual J to what the heat pump is rated for: https://www.waterfurnace.com/literature/5series/sd2500an.pdf Whether you have the single stage or dual stage compressor model, they both top out at about 55k BTU. More support that you are quite undersized when using a closed ground loop.
The manual J might not be accurate. It ran all night because you took some heat strips out. I would say you are undersized if resistance heating is costing you that much. It isn't a small house.
So you used over $8000 in propane annually? And now you used 5600 kWh ($600) over your regular bill in December, so you are clearly doing already much better, correct? So if this goes on for 4 months (Dec-Mar) and a couple shoulder months, your are probably looking at a total of $3000 per year for your geo system to operate. Your heat load of 77 KBTU/h or 88kBTU/h seems to fit, if you are putting in 55 KBTU/H from your heat pump, and 32KBTU/h from your heat elements, 87 KBTU/h total during this cold span. So I would say the system runs as expected, and is performing as it should. The rest is your house, which needs a lot of energy. Nothing your heating contractor can do about, only you, who's house it is. I would predict that for a few thousand $$ you can take care of 80-90% of the deficiencies of your house, which should be able to get rid of the supplement heat usage.
Now I am more concerned. I found an additional report by the company selected to install and they came up with a load of 114,000 at 17 degrees. Doesn't that indicate I need more like 9 tons of capacity, not 6? This is the unit I have: NDV072 6 ton, 2-stage, Vertical "5 series" Unit by WaterFurnace. Scroll Compressor, 5 spd ECM fan motor, Aurora control. Factory warranty is 10 years on parts w/5 year labor allowance.
I appreciate all the quick responses. Docjenser, completely agree, I will be better off from a cost perspective even with the high AUX usage. But cost is one thing, the wife being upset because the house is cold is quite another. If I can't insulate my way to an equilibrium with my 6 ton unit, how feasible is it to retrofit in an additional smaller 2 or 3 ton unit into the system? Regards, Nathan
Always cheaper to insulate. Cheaper upfront, cheaper to operate, more comfortable. If your wife is uncomfortable during those extreme conditions, turn on the other part of the heat element. Those reports are not worth much, no one can accurately know how good your insulation is in your walls in an old house. Sure you might have 10-12 tons load during extreme cold spans, which is why you have 64 KBTU/h of electric supplement heat. But it also means your heat pump has enough capacity to carry 90% of your total annual heat load. Seems like your house is very leaky and you get a great bang for the buck to spend a few thousand $$$ of making it tighter. Also makes the wife happy too....that is priceless!
docjenser, indeed keeping the wife happy is priceless! We are in a rare weather event, I will work on insulation first. Thanks for your assistance.
Your experiencing a cold spell right now that is abnormal for a extended period of time too. Also with the system being so new still, Do you think your installer “Sold” you on the savings you will/should see during normal winter weather conditions? If that’s the case, we will return to normal weather conditions and you will be more satisfied when the “new buyers remorse” period ends. I see this all too often when new Geo customers over think the short term savings with the bigger picture savings while second guessing every move they made. P.S. Those Aux. heat strips are installed for this exact reason though....enjoy them when they are needed.
I didn't buy the Geothermal to save money in the short term. I bought it to shield myself from long term fluctuations in propane prices. I also previously had Geothermal in a home I rented for 2 years, and loved it. You don't think its a problem that the contractor's own manual J shows sizing of 9 tons and they installed 6, while admitting to me after I paid that I actually needed to do $5k more insulating for it to work effectively?
No, geo, per manual J and building code, your heating equipment is only designed to carry 98% of the annual heat load, but that is usually 80% of the peak load. The other 20% you usually supplement with strip heat. My IGSPA manual still says that geo should be sized for the cooling load, and the rest you supplement with electricity. $5K is cheap, adding $20K now for another heatpump is more expensive upfront. With the insulation, you now need less energy, not just at peak time, for the whole year. Plus the wife would like it too.....no more cold drafts.
I need some basic education on the issue of sizing systems, please. According to Nathan's post #7 above, he stated that another installation calculations had sized his system at 114 kBTU at 17 degrees. I'm in Minnesota, and my system was calculated using -17 degree F (not +17 F) as the design outdoor temperature heating condition. I can't image Michigan is much different than Minnesota from an outside design temperature standpoint, so even with the 9-ton system as stated in the post, it still would not be large enough to keep up--at least on paper--during temps any lower than 17F (?). Maybe I am not understanding how design conditions relate to real world conditions. I have an early 1980's home with 2000 fin sq.ft., 700 unconditioned, unfinished sq.ft. in the basement, and this last cold snap (1-28-19 thru 1-31-2019) kept us below zero for 3 days with -30 F peak lows, but the our 3-ton vertical closed loop GSHP kept the house at setpoint without any aux heating. It ran nearly continuously on second stage for the last three days and was starting to lose ground the second day, but it kept up until it got warmer . Loop temps got really low (27 deg EWT) but was rock solid dT both air and water side. I agree that all energy conservation should be done prior to GSHP sizing, but shouldn't the installer have set the proper Owner expectations prior to the installation? Lastly--Doc: You meant "heating" load above, not "cooling", correct?
No....the IGSHPA manual insisted that geo system should be designed for cooling, and the rest should be supplemented with strip heat....that was 8 years ago. You have the best example, very efficient house in cold climate. What is one supposed to base the heat loss calculation on? Air infiltration and heat flux? How do I know what is in the walls, without opening them all up? Certain things are obvious, others are not. Like a builder or owner not putting insulation in. Or an air barrier. And then blame the heating system....I have that in new builds and retrofits.... If someone has a leaky house which can be easily addressed, why would you put in twice the size of a heating system, and much higher upfront cost, and then pay for much higher operational costs? The problems are not new, they have simply being masked in the past by grossly oversized gas or oil heating systems. Now we are obligated by code to more precision match the supposed heat load of the house. Yes, I set expectations, double the size of the system, and being still 50% short. Homeowners always promise that they will put in the recommended insulation, when I ask them if then want to spend $30K on a 4 tons system, or $60K on a 10 ton system. After the 4 ton system does not hold up, they call me. Never upgraded the insulation as they said they would. Conveniently forgot, complain about high supplement heat or system not keeping up. Always the same story. Just got back from one this morning. We put it in our contracts now, so that there is no debate over what was recommended and discussed in terms of insulation and air tightness. It is building code and energy preservation code now!
You can find the 99% heating design temperature for your location from this link: https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County Level Design Temperature Reference Guide - 2015-06-24.pdf Minnesota varies from -6F to -21F depending on location. Michigan varies from +10F to -9F depending on location. Michigan winter temperatures are likely higher due to the temperature moderating effects of the water surrounding it, i.e. the Great Lakes.
