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Discussion Starter · #1 ·
I have a 3 ton Trane dual fuel heat pump with LP furnace as back up . The unit is from 1996 and is on its way out . I live in north Georgia so winter temps generally never dip below 25 degrees . I am considering having the system replaced with a ducted mini split of equal 3 ton size . My current system is installed in the basement and is an upflow design . The mini split I am considering either Mitsubishi or LG is also an upflow design .

In a perfect world I could eliminate the LP for furnace back up heat and just use it for a cook top, water heater and an un-vented wall mounted heater we have as back up . I know a modern mini split is no comparison to a 24 year old heat pump but would this be a good way to go ? Our electric bills with the old heat pump ran in the 100.00 - 200.00 per month depending on weather and number of guests .

I have a 24K Mitsubishi single head mini split in my 24x26 man cave garage and it does a fantastic job , but I am NOT familar with a more standard like upflow plenum for a whole house . Any feedback is appreciated .
 

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3 tons may not be handle heating capacity to carry the entire load, your propane furnace is probably between 55 and 75k btu per hour output.

3 ton is 36k btu/hr max - the best ones can maintain full capacity well below freezing.

I would not pull the plug on propane unless it can be done without resorting to electric resistance backup.

The ducted mini-splits may not be suitable for air ducts designed for a central heatpump. Different flow rates and static pressure levels.

There are central heatpumps with the same/similar technology.

Daikin makes one of them - probably lots of $$ though.
 

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What size is your gas furnace, and how long did it run when it was 25 outside?
 

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3 tons may not be handle heating capacity to carry the entire load, your propane furnace is probably between 55 and 75k btu per hour output.
For some reason i was thinking 40k units don't have 3 ton drives when a lot of them do - ignore this part of my post please.

Stupid error on my part.
 

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The big players in minisplits all make conventional, residential style air handlers that can handle high static conventional duct.
Samsung, Mitsubishi, and others make these systems.
I don’t care much for LG. Several of my customers have their equipment and I find it inferior other manufacturers, especially their multi head and VRF equipment.
Samsung and Mitsubishi are my favored manufacturers, with Mitsubishi being basically king of the mountain.
It is possible to do what you want.
Daikin makes a minisplit system that you can use with a conventional furnace. Very efficient and it can provide heat running in heat pump mode at very low outdoor temperature.
 

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Discussion Starter · #6 ·
Good advice guys thanks . I think I will stick with a more conventional system , either a high SEER AC and LP furnace or a high SEER heat pump/dual fuel with LP back up . I received a quote yesterday for a 14 SEER American Standard AC with a LP furnace installed for $6900.00 . One thousand of that was taping/sealing the existing flex duct and insulating the register boots . For $1300.00 more it can be a 16 SEER system . The plan is to stay in this house until the dirt nap :biggrin2: so I have time ( hopefully ) to recoup the price of what ever I choose . Any thoughts on the above ?

Today the HVAC guy that has been repairing my current system will provide three quotes , baseline simple 14 - 16 SEER AC/furnace , 16 - 18 SEER heat pump dual fuel and top of the line inverter style heat pump with electric strip back up . The first quote for 6900.00 is using all of the existing duct work , the quotes today will include all new metal duct work sealed and insulated . Seems like everyone is pretty much offering 10 year parts/compressor warranty but this guy indicated he would also do either 3 or 5 year labor warranty which is attractive . Both guys had indicated there is a 6 - 7 % price hike coming the end of January form most/all the manufacturers so I am trying to purchase in time for that savings .
 

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The 10 year parts warranty is only if the system is registered. If not it drops to 5 years. You’ll need to verify your installer does this, but it is something you can do online.
Don’t pay a bunch of attention to high seer numbers, focus on proper sizing, installation and commissioning.
How much did the current system run? How did it do on very hot or very cold days? Did it cycle or run constantly?
 

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Discussion Starter · #8 ·
The 10 year parts warranty is only if the system is registered. If not it drops to 5 years. You’ll need to verify your installer does this, but it is something you can do online.
Don’t pay a bunch of attention to high seer numbers, focus on proper sizing, installation and commissioning.
How much did the current system run? How did it do on very hot or very cold days? Did it cycle or run constantly?
Of course any system has to be registered for the warranty , I would make sure that happens . The current 3 ton system I feel is the right size but I " may " go to 3.5 ton only because I want two additional ducts run in the basement . Those ducts will be for a future bathroom and game room .

Overall I have been happy with the performance of the current system , it's just now at end of life and a lot has changed since 1996 .
 

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It will get expensive modifying your existing duct for a larger system, no?
Don’t play with sizing without a load calculation. Bigger isn’t better.
Basements normally need dehumidification and a little bit of heat. You’d likely be better off with a dehumidifier and mini split heat pump for the basement zone.
 

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Of course any system has to be registered for the warranty , I would make sure that happens . The current 3 ton system I feel is the right size but I " may " go to 3.5 ton only because I want two additional ducts run in the basement . Those ducts will be for a future bathroom and game room .

Overall I have been happy with the performance of the current system , it's just now at end of life and a lot has changed since 1996 .



A basement bathroom and game room won't need much cooling, and don't require a 1/2 ton increase in A/C size.
 

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In Georgia with a low of 25F, I would not be worried about using a minisplit for primary heating or manually disabling backup heat operation.

the downside to minisplits is they seem to stop working without warning. As to say the computer in it will decide something is wrong and then not operate, not to say that they fail more or less frequently than a standard heat pump. they can be more difficult to troubleshoot, and fewer service companies know what to do with them.

I talked a friend in an electric/propane area into one of the variable speed Lennox systems and he absolutely loves it. went from a 2.5 ton single stage to a 3 ton VS & communicating T-stat and the house is so much more comfortable that they dropped the temp from 70 to 68. also it saves them thousands of dollars a year due to it's better cold weather performance and lack of electric backup heat use.
 

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What is the goal here?

I see no value in putting in a straight a/c and another furnace. What do you gain? You can end up with higher heating bills than you have now.

Check your utility rates because it may be cheaper to run a heatpump than propane.

Get a load calculation done - if a 3 ton heatpump can maintain setpoint in the coldest weather you get, dual fuel is a total waste of money.

You may not need a cold climate style inverter heatpump to do this. (or u may)

You can have air handler and heat strips are only used to temper the air during defrost cycles. (and for emergency heat if the heatpump breaks down)

It can be wired up to never bring heat strips on during normal operation.
 

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Discussion Starter · #13 ·
The goal is to replace my dieing dual fuel setup with something more efficient and as reasonably priced as possible . I received three quotes yesterday from the company that has been servicing my current setup .

1. A 14 SEER AC system with a 92 % efficient LP furnace for $5600.00 installed . Add $750.00 for 16 SEER . System has a 10 year warranty , 20 year heat exchanger and 3 years labor.

2. A 16 SEER dual fuel heat pump with LP furnace back up . This includes a 80,000 BTU furnace with the same warranty as above for $7800.00 installed.

3. A 17.5 SEER heat pump with inverter compressor and variable speed air handler . Has Wifi thermostat and 10KW heat strips as back up . Warranty is 10 years parts/compressor . Installed price is $7975.00

All units listed above will include in the installation new metal duct work vs. the flexible ducts I currently have . I think metal is a better way to go and they will be sealed/insulated . My current system being 1996 vintage may be 8 or 10 SEER so anything I install today will be more efficient . Line # 1 is probably the most simple option and there is something to be said about the KISS principle :smile: Line # 2 a little more complex and line # 3 the most complex . Now I have to decide which to go with .
 

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I would not suggest just an LP furnace.
LP pricing can be volatile, and I know a few accounts of mine where it would be cheaper to have a heat pump with electric backup then just an LP furnace.
Remember, as you get into the high efficiency variable speed equipment, you need to make sure the company knows the equipment and can service it.
Anybody can sell it but if they don’t know how it works your out of luck when it breaks.
 

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Having snooped and calculated my energy costs versus my neighbors since his electric meter is easy to snoop, it turns out that I wish I had a geo-thermal heat pump like he had installed 3 years ago. I doubted his wisdom at the time since we have NG available but it looks like the ROI will be faster than the 10 years the installing company claimed!

If I lived where propane had to be considered, I wouldn't hesitate to capitalize a geo system, providing of course that I was at least 20 years younger.
 

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80k btu is a huge furnace for a area that doesn't drop below 25.

what size is existing?

a load calculation can help u with equipment selection, if a heatpump can keep up without backup i sure wouldn't bother getting a furnace.
 

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option 3 is what i'd look at. ask for a quote on a 2 stage with a heat-pump aware t-stat for comparison if it's pushing the budget (plenty of options out there, my favorite is the honeywell prestige redlink system).

if it doesn't add much cost, electric backup should be cheap (heaters are cheap, labor for running wires not so much). 5-10kW should be enough to survive on, and you can just leave the breaker off to the backup heat, or configure the t-stat to lock it out above 10-15F.

the inverter/communicating t-stat systems are usually much smarter about backup heat than an el-cheapo t-stat will be.
 

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Discussion Starter · #18 ·
The existing duel fuel LP furnace is a 75K and was installed in 1996 when the home was built . I will ask the guy why he quoted an 80K . I am sold on inverter technology , I like everything about it except potential high dollar repairs . My Mitsubishi 24K mini split in my 2 car man cave is a great HVAC , whisper quiet and a miser on electricity . If it croaks prematurely it's just a garage and I don't have to repair right away .

If the inverter heat pump croaks in the house repairs are needed pretty much immediately . Maybe I am being overly cautious and these systems are so reliable it's not an issue . I guess for the 10 year warranty period just sit back and don't worry :biggrin2: Or maybe the difference in repair costs is not as great as I perceive them to be ?

I have a 3rd company coming to the house this morning to see what they have/recommend . After I talk to them and receive their quotes I will have enough info to make an informed decision .
 

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Discussion Starter · #19 ·
Third company came and we discussed several options , the most attractive option to me is their Daikin 3 ton inverter heat pump with a 40K dual fuel LP furnace . I believe for my climate this is the most efficient/cost effective way to go . A 17 SEER inverter heat pump , a 40 K dual fuel LP furnace and a " communication " thermostat with Wifi for $8400.00 installed . They will use the existing ducting but add two additional runs in the basement for a future bathroom and game room . The unit carries a 12 year parts and labor warranty .

For our area they would set the balance point at 17 degrees , so 99 % of the time it will heat in heat pump mode so very little LP usage . It is their " Fit " series . Apparently this particular setup will be " officially " available for sale starting next week , it has been in test mode for the past year in various locations across the US . The Fit has been available for a while now as an AC unit only with stand alone furnace or heat strips , the dual fuel is what's new . Any thoughts/comments ?
 

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I think you're working with too little information.

How much has propane been historically? What about electricity?

How much heat does the house actually need?

What would the balance point be with different heatpumps?

Will an inverter heatpump alone be able to maintain setpoint without backup? What's cheaper to run in cold weather - heatpump or furnace?

A propane furnace may be a total waste of money if you pay extra for a heatpump which can keep up at low temps.

Utility rates, a load calculation and performance data at various outdoor temps are required to make a sound decision. Without calculations, you're guessing.

You also need a contractor who can make sure the air ducts are large enough for 3 ton. The variable speed blower controllers can burn out prematurely on undersized air ducts.
 
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