First of all a 16 or 17-year-old geothermal HP should only be at about the half way mark of its useful life. I’m not buying the argument that the ‘coil’ gets pitted and needs to be changed every 10-years.

I’m assuming the tech is referring the water-to-refrigerant heat exchange coil when he mentions the ‘coil’. This should be a pressurized closed system with no air in that loop. I suspect that the ground loop was not installed with ‘Best Practices’ that is resulting in premature failure of this coil.

Periodic maintenance requires that the ground loop fluid be monitored, recorded and a written detailed diagnostic with all measurements be left at the HP for antifreeze concentration levels and proper levels of fluid inhibitors to prevent undue component wear as well as prescribed overall fluid pressure in the ground loops. In fact you should have an, ‘As Built Book’ that recorded all the design parameters, start up procedures and measurements in great detail. This is like having an EKG of your system as installed while it’s still hopefully running OK so that any competent tech can come on site, see and easily understand how it’s 'supposed' to run and what might be going on without wasting their time and your money.

I would strongly suggest having a conversation with a service or installation manager at Waterfurnace to discuss this matter. This repair won’t be a freebie but must be done completely and properly. You can ask Waterfurnace if a Cupronickel heat exchanger might be advisable in your case.

If your system has an underlying installation deficiency that is not corrected, you might have the same recurring problem down the line with a brand new unit.

I think your tech is telling you a story. I doubt Waterfurnace would remain in business if replacing these expensive parts is par for the course.

Speak to Waterfurnace; drill down till you get logical answers that satisfy you.

Post back.

IMPO

SR

fsq4cw, Thanks for the response. I'm pleasantly surprised to hear that the expected life span of my system is around 35 years. I know WF makes a quality product and this confirms it.

Let me add a little more clarification. The idea of replacing my current system is mine and primarily based on the 26% (I posted the wrong % above) tax credit afforded me if I do it in 2020. My WF tech did not suggest it to me. He said my system was working fine at my annual maintenance visit last spring. He did say he'd price me a system if I wanted to change.

The system was already installed when we bought the house in 2003. Having no prior experience with geo-thermal systems I contacted a couple of local HVAC companies for their input. Both said they'd be leery (my words) and offered to install me a "conventional" system. (Flash forward to the present and both companies are now installing geo-thermal.) I told the seller I was a little skeptical of this new technology and he had the installer write me a letter detailing the system and his installation. At that time he'd worked for WF for 10 years and had installed his first geo system in 1983. I had no concerns after the letter and talks following.

I took the "coil" replacement to be more of a favor. I was nearing the end of my 10 year warranty period, he thought that there might be some pitting and we could replace the part now at no cost.

So, to recap, would it make sense to replace a working 17 yo WF system now, with 26% of the cost subsidized, experiencing some savings from the increased efficiency, being able to plan the installation at my convenience and reset the 10 year warranty period? Or, wait until the system fails, replace at full cost, perhaps many years from now?

If I can expect 18 years more of trouble free service then the answer is obviously "No".

Replace or wait is more of a financial question. If you plan to live in this house another 15 years, then it may makes financial sense to do it now. If you will in be the house for less time, then are probably better off investing the money with a 2-3% return and using the growth to pay for future repairs.

If you plan to use the existing ground loops, then I don't think a new system will be more efficient. I would be interested in Fsq4cw's opinion on this.

The other thing you should consider is what happens in 2022 if Congress does not reinstate the tax credits? Will the current residential geothermal businesses continue to install and systems? I would be worried about investing money in a new Water Furnace and then finding out there are no nearby geothermal dealers to service warranty claims.

Thanks for the comments. I'll discuss upgrading with my WF tech next month when he's out for annual maintenance.

Re: Mike_home

“Replace or wait is more of a financial question. If you plan to live in this house another 15 years, then it may makes financial sense to do it now.”

I agree with this statement.

“ The other thing you should consider is what happens in 2022 if Congress does not reinstate the tax credits? Will the current residential geothermal businesses continue to install and systems? I would be worried about investing money in a new Water Furnace and then finding out there are no nearby geothermal dealers to service warranty claims.”

I would not be worried about this at all. Geothermal will continue to be a viable business. The loss of tax credits will bring with it the exit of sub par contractors that appear on the scene when incentives appear to make a fast buck. The OP mentioned that the installer of their geothermal system has being installing geo since 1983. I would say that they are likely in very good hands.

“If you plan to use the existing ground loops, then I don't think a new system will be more efficient. I would be interested in Fsq4cw's opinion on this.”

A new system will be more efficient. Many changes and improvements have been developed since the original installation in 2003 with a HP that surely predates 2003. Todays WF HP are ‘Energy Star’ rated that is an improvement in and of itself with the imposition of much higher standards than existed in 2003.

If the OP chooses the WF Series 7, additional efficiencies will be achieved with the use of variable speed technologies that in addition to variable speed blower fans also include inverter driven variable speed compressors and inverter driven variable speed flow centres. Another important development in the high-end residential HVAC market place has been the introduction of microprocessor controlled Electronic Expansion Valves (EXV) instead of Thermal Expansion Valves (TXV) that are more ‘mechanical’ and less precise in nature.

Together, these improvements will bring greater efficiency (COP up to 5.1 from about 3.5) with longer run times, better dehumidification and greater comfort.

I will say this, that WF Series 7 being in a different/higher class requires installers with greater experience and higher competency to install it right, to better achieve in the ‘real world’ the ‘theoretically’ achieved COP efficiencies created in a lab.

Put another way that is more relatable on this site, just as conventional HVAC that involves the installation and implementation of zoning requires a specialized installer, so too does the installation of a fully variable geothermal heat pump system require a more experienced and technically knowledgeable designer/installer. WF Series 5 might

be a safer choice (up to 4.3 COP) due to the complexity of Series 7.

IMPO

SR

@fsq4cw, my contractor said that installation of a WF Series 7 in a space where the temperature exceeds 120 degrees may void the warranty. My unit is in my attic and I’ve seen the temperature get to 126. Are you aware of this being an issue? I’ve not seen It in any of the literature. I much prefer the extra efficiencies of this unit if possible. TIA

Your dealer is right to point this out, this might void your warranty - especially if you should develop recurring issues, Waterfurnace might ask questions about ambient temperature of unit location.

This is stated in the Installation Manual: See page 5, ‘Unit Location’

Waterfurnace Series 7 Installation Manual

A few things to keep in mind:

Operating in that hot an environment might impact efficiency (COP) that you’re paying a premium for at purchase. There’s a good chance you may never realize the performance promised and invested money for no or little benefit.

Series 7 is far more sophisticated than your original HP and will have more (heat) sensitive electronics that the original unit does not have, such as electronically controlled inverters for everything that is viable speed (compressor, blower fan motor, flow centre circulator(s), electronic expansion valve(s) (EEV). All these components will be expensive to replace (parts and labour).

That’s the down side. There is an upside.

Aside from the circulators in the flow centre that might be able to handle the heat because those same basic circulators are used in hydronic hot water heating systems that might be circulating hot water as hot as 180˚F - all the other above mentioned components are enclosed within the envelope of the HP enclosure that is quite cold while operating. However, internal temperatures might also rise within the HP if operating at lower speeds due to reduced demand (cold air flow within the HP).

You would be better off taking your installer’s advice and see where else the HP might be located although that will involve major modifications (electrical, geo-exchange piping, supply & return ductwork - at a minimum).

On the other hand, Waterfurnace Series 5 ‘Unit Location’ (Page 5) mentions no specific temperature limit - only ‘excessive heat’ that is ‘undefined’.

Waterfurnace Series 5 Installation Manual

You might discuss that with your installer too.

Hope this helps.

IMPO

SR

@fsq4cw, Thank you so much for your comments.

No problem, that was a ‘Professional Consultation’ - the invoice is in your mail box (LOL)!

Glad if I can help.

BTW: The performance of the desuperheater might also be impacted if operating in an extreme environment; also something to be discussed with your installer (output capacity, efficiency, etc.).

IMPO

SR

@fsq4cw, Still waiting for my consult billing. Must have gotten lost in the mail.

Met with my hvac guy today. He said a split system looks to be an option and asked if I wanted to consider that. I like the fact that it gets the compressor (and its weight) out of the attic and puts it under the house. Of course the cost will be more but he said it might allow us to go with the Series 7. In looking at the specs for the 7 (050) it looked like that unit had fewer cooling btus than the Series 5, model 064, I was originally considering.

Am I reading that chart correctly? Doesn’t seem that I would want fewer cooling btus than my current unit.

TIA, add it to my bill.

Without going much further, Series 7 (050) is nominally a 4-ton unit while Series-5 (064) is nominally a 5-ton unit so I would expect the Series-5 (064) to have greater output - all other things being equal!

You might be better serviced by a Series-5 2-speed compressor unit than by the Series-7 variable speed compressor unit. The indoor air handler should be variable speed in both cases.

When reading specs be sure you're reading the same size (capacity) unit and the same variables, such as flow rates (gpm), ground temperature, Entering Air Temperature (EAT), Leaving Air Temperature (LAT), Entering Water Temperature (EWT), 'Full Load/Part Load', Heating Mode, Cooling Mode, etc. - everything counts and makes a BIG difference in heating/cooling, comfort - and especially in your wallet!

IMPO

SR

Warning Signs: When you may need to replace your furnace.

https://www.air-conditioning-heating.org/

16-20 years: The average life expectancy of a furnace

Energy bills going up

Furnace repairs: furnace incurs most breakdowns in last two years

Thermostat not keeping you comfortable

Strange noises

One more comment about size, any deficiency in ground loop design or inefficiency of ground loop performance will limit heat pump capacity regardless of its rated output!

IMPO

SR

@fsq4cw, after discussing this with my hvac guy I decided to go with the Series 5 split system. We’ve been fortunate that we haven’t had any 100+ degree days the last 2 summers but we’ve had summers in the past where we’ve had 30+. I didn’t want to give up those extra btus for those days.

Thanks again for helping me in making this decision.

I think you’re making an excellent choice. You didn’t specify what city you live in but even if you lived in Miami that has some of the warmest ground temperatures of ‘The Lower 48’ in the summertime (+78˚F), you would still have about 5-tons of total cooling.

I don’t think you’ll have to worry much about +100˚F days. Just let it run and do its thing.

Just be sure the unit you purchase is a ‘Dual Speed Compressor’ unit! (Series-5 Model 064 is)

My preference is to always have the HP compressor unit in a split system installed in a 'Conditioned' (protected) space.

IMPO

SR