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Old 01-11-2020, 03:18 PM   #1
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can a ducted mini split replace a dual fuel heat pump ?


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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Old 01-11-2020, 03:22 PM   #2
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 01-11-2020, 05:32 PM   #3
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Re: can a ducted mini split replace a dual fuel heat pump ?


What size is your gas furnace, and how long did it run when it was 25 outside?
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Old 01-11-2020, 06:17 PM   #4
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Re: can a ducted mini split replace a dual fuel heat pump ?


Quote:
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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Old 01-11-2020, 09:20 PM   #5
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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Old 01-12-2020, 08:09 AM   #6
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Re: can a ducted mini split replace a dual fuel heat pump ?


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 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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Old 01-12-2020, 08:13 AM   #7
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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Old 01-12-2020, 08:36 AM   #8
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Re: can a ducted mini split replace a dual fuel heat pump ?


Quote:
Originally Posted by roughneck View Post
The 10 year parts warranty is only if the system is registered. If not it drops to 5 years. Youíll need to verify your installer does this, but it is something you can do online.
Donít 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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Old 01-12-2020, 08:39 AM   #9
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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Old 01-12-2020, 10:20 AM   #10
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Re: can a ducted mini split replace a dual fuel heat pump ?


Quote:
Originally Posted by Porsche986S View Post
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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Old 01-12-2020, 12:04 PM   #11
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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Old 01-12-2020, 12:15 PM   #12
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 01-13-2020, 12:28 PM   #13
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Re: can a ducted mini split replace a dual fuel heat pump ?


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 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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Old 01-13-2020, 12:47 PM   #14
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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Old 01-13-2020, 01:08 PM   #15
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Re: can a ducted mini split replace a dual fuel heat pump ?


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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