Dual-fuel heat pump (was 'Multiple zones')

[Chevsky]

I'm looking at replacing my 20-year old heating & cooling system. It's 2 zones -- meaning it's two separate, complete, independent systems--one is 100KBTU, the other 80KBTU, home is 2900 sqft.

EDIT: Cut to the chase -- I abandoned the idea of a MULTI-SPLIT-DUCTED setup. I had thought all the multi-zone HPs I saw online would be compatible with traditional 24v thermostat and a HP--lineset--coil+furnace arrangement. Those multi-zone HPs are for mini-split style wiring, so a single HP condenser connected to multiple inside "heads"--wall units, and ceiling/wall cassettes. Although I found Daikin's communicating VFV system, and Carrier's 24V interface kit, these would be too complicated to build, too expensive, and difficult to configure with AHRI certification for the Mass rebates.

---the rest of the thread is left as is---

Does anyone know if it's possible to connect two hybrid dual-fuel style interior handlers to a single outside HP unit? Ultimately, I'd like to reduce our LP use as much as possible, and "comfort" is less of a concern (we have a fireplace if it comes down to that).

I've described what I'm thinking below -- if anyone has recommendation then I'm open to your suggestions. Thank you.

My Thoughts -- I'm interested in a Dual Fuel (heat-pump and LP gas) because I'm in Massachusetts. If possible, a single outside unit feeding two inside air-handler+furnace combo units, much the way they do with mini-splits. The reasoning for a single outside unit is because the second zone gets much less use than the primary zone, and it would be nice to save the cost of the second outside unit. Also, since the secondary zone gets less use, I'd consider skipping the dual-fuel on that space, making it just a simpler ducted mini-split style connected up to the existing air ducts. (There are no bathrooms--thus no plumbed water--upstairs to be damaged if we closed down the space during super cold snaps.)

Why it's laid out this way -- Currently each system has it's own interior air handler with LP furnace, and its own outside AC compressor. The layout of the house is such that there isn't a convenient way to bridge the two spaces with duct-work, so the original installer just used two separate systems. The first system is the main house, with the air handler in the basement, and the second system is a large family room and office over the garage with the furnace in an attic space and using smaller-sized units. The upstairs system's AC coolant lines run down into the basement, and then along-side the primary zone's lines to the compressors sitting outside side-by-side. Both systems, and the hot water heater, use the same single-flue chimney.

When going 96%+ efficient I'd switch to low-temp exhaust and could remove the chimney (that is, if replace the water heater too). And if I remove the chimney this would create a passage for supply/return air ducting from the secondary space's air handler to the location of the primary furnace, thus negating the need for two separate systems. But I'm not sure I'd want to do that anyway, as the duct distances would be long, and if we reclaim the chimney footprint then we'd prefer other uses... and well, perhaps the trade off is A) cost of two air-handlers, vs B) cost of chimney removal and of running extra new ducts. (I expect there are new building codes that would dictate that upon replacement I can't continue using a common chimney flue this way. But the update would mean I'm not using this chimney for the furnaces anyway, but still for the hot-water, unless it's also replaced.)

So it seems that simplest replacements would be 1) to go with two separate dual-fuel/hybrid systems (or one duel-fuel and one ducted mini-split), or 2) with an intergrated, two-zone (via refrigerant lines) system with a single outside unit, and two interior units--either both dual-fuel HP+LP hybrid, or one hybrid and one HP-only. This is my preference, rather than removing the chimney and connecting the duct-work together with single system but with two zones using air dampers, etc.

I was told by an installer that although mini-splits have this option--one outside unit feeding multiple inside units--that dual-fuel hybrid systems don't. My initial impression is, "why not? Are you sure about that?" And after some research, I don't see any "packaged" system with this option, but I also don't see any evidence that I can't just buy à la carte two hybrid air handlers, one outside unit that has multiple zone connections, and two line-sets. Is it something to do with the outside temp cutoff of the HP and switch to gas? I'm ok with both zones switching to LP regardless if one zone is calling for much less heat compared to other; or if 2nd zone is HP-only and during a cold day and the primary zone switches to LP and the 2nd zone gets no heat because it doesn't have a hybrid backup--with today's super low-temp heat pumps I could set the cut-off low so those situations will be very rare.

 

[John Gayewski]

I'm looking at replacing my 20-year old heating & cooling system. It's 2 zones -- meaning it's two separate, complete, independent systems--one is 100KBTU, the other 80KBTU, home is 2900 sqft.

Does anyone know if it's possible to connect two hybrid dual-fuel style interior handlers to a single outside HP unit? Ultimately, I'd like to reduce our LP use as much as possible, and "comfort" is less of a concern (we have a fireplace if it comes down to that).

I've described what I'm thinking below -- if anyone has recommendation then I'm open to your suggestions. Thank you.

My Thoughts -- I'm interested in a Dual Fuel (heat-pump and LP gas) because I'm in Massachusetts. If possible, a single outside unit feeding two inside air-handler+furnace combo units, much the way they do with mini-splits. The reasoning for a single outside unit is because the second zone gets much less use than the primary zone, and it would be nice to save the cost of the second outside unit. Also, since the secondary zone gets less use, I'd consider skipping the dual-fuel on that space, making it just a simpler ducted mini-split style connected up to the existing air ducts. (There are no bathrooms--thus no plumbed water--upstairs to be damaged if we closed down the space during super cold snaps.)

Why it's laid out this way -- Currently each system has it's own interior air handler with LP furnace, and its own outside AC compressor. The layout of the house is such that there isn't a convenient way to bridge the two spaces with duct-work, so the original installer just used two separate systems. The first system is the main house, with the air handler in the basement, and the second system is a large family room and office over the garage with the furnace in an attic space and using smaller-sized units. The upstairs system's AC coolant lines run down into the basement, and then along-side the primary zone's lines to the compressors sitting outside side-by-side. Both systems, and the hot water heater, use the same single-flue chimney.

When going 96%+ efficient I'd switch to low-temp exhaust and could remove the chimney (that is, if replace the water heater too). And if I remove the chimney this would create a passage for supply/return air ducting from the secondary space's air handler to the location of the primary furnace, thus negating the need for two separate systems. But I'm not sure I'd want to do that anyway, as the duct distances would be long, and if we reclaim the chimney footprint then we'd prefer other uses... and well, perhaps the trade off is A) cost of two air-handlers, vs B) cost of chimney removal and of running extra new ducts. (I expect there are new building codes that would dictate that upon replacement I can't continue using a common chimney flue this way. But the update would mean I'm not using this chimney for the furnaces anyway, but still for the hot-water, unless it's also replaced.)

So it seems that simplest replacements would be 1) to go with two separate dual-fuel/hybrid systems (or one duel-fuel and one ducted mini-split), or 2) with an intergrated, two-zone (via refrigerant lines) system with a single outside unit, and two interior units--either both dual-fuel HP+LP hyprid, or one hybrid and one HP-only. This is my preference, rather than removing the chimney and connecting the duct-work together with single system but with two zones using air dampers, etc.

I was told by an installer that although mini-splits have this option--one outside unit feeding multiple inside units--that dual-fuel hybrid systems don't. My initial impression is, "why not? Are you sure about that?" And after some research, I don't see any "packaged" system with this option, but I also don't see any evidence that I can't just buy à la carte two hybrid air handlers, one outside unit that has multiple zone connections, and two line-sets.

I think having two separate systems is better than sharing an outdoor compressor. If one breaks down you could be weeks away from relief. Especially with heat pump stuff. I think most people would rather have two systems as long as they are both effeciant you should be using the same amount of energy.

I like the "duel fuel" heat pump/furnace idea.

You said you had a fireplace but also would tear out your chimney? Are these two separate structures?

 

[Sponsor]

 

[Chevsky]

I think having two separate systems is better than sharing an outdoor compressor. If one breaks down you could be weeks away from relief. Especially with heat pump stuff. I think most people would rather have two systems as long as they are both effeciant you should be using the same amount of energy.

I like the "duel fuel" heat pump/furnace idea.

You said you had a fireplace but also would tear out your chimney? Are these two separate structures?

Yes -- Two different chimneys.
The fireplace is in a large central chimney, but the furnaces use a small single-flue chimney located nearer to the joining of the two "halves" of the house. In fact, the large fireplace chimney has a second unused flue, complete with spare LP line to the area in the basement by the chimney complete with a flue port -- it looks like the builder imagined perhaps a wood shop with gas stove. Many possibilities

 

[Fitter30]

Two systems would better because cause haven't found one other than a mini split that wouldn't have the option of dual fuel. Minis use variable refrigerant flow along with variable air flow and haven't seen one with a vertical ahu just horizontal. Contractor is more important the brand and the higher efficiency equipment takes a better trained service person. If using a mini 2nd floor use hyper heat unit works better at low temps.

 

[Chevsky]

Two systems would better because cause haven't found one other than a mini split that wouldn't have the option of dual fuel. Minis use variable refrigerant flow along with variable air flow and haven't seen one with a vertical ahu just horizontal. Contractor is more important the brand and the higher efficiency equipment takes a better trained service person. If using a mini 2nd floor use hyper heat unit works better at low temps.

Is "Hyper Heat" a Mitsubishi trademark name? Amazing lockout temp at -22F!

But that system is very expensive ($8,500 for 42,000BTU @ 15.4 seer, uninstalled), and tho I agree it would be a technically good choice if opting for non-hybrid on 2nd zone, the high cost makes it less attractive when we don't use that space much and probably don't need it for it's design temps. Hell we'll probably never see those kind of temps here ever. And since a dedicated hybrid system for this zone is overall lower install cost... Even the cheapo "packaged" HP-only units (60,000BTU @ 17 seer) is priced at $4,500.

For aesthetic reasons it would be nice to use the same brand for both systems, even if not the same model for the two. (like having matching compressors on the two cement pads outside)

I still think there are systems that do multi air handlers (zones) insides with single outside compressors--there are being advertised, and DAIKIN seems to have it (even with mix-n-match air handler types--see below--that pic is from GreenHome Institute presentation of [Mitsubish's] Intelli-Heat system). But I hear what you all are saying -- no benefit in trying to take the multi-zone, variable-refrigerant-flow concept to a full-house multizone, ducted, hybrid, non-mini-split design, when I can simplify the install and maintenance by going more mainstream. Especially when one zone is a pseudo non-living space (tho we do host over the holidays get use out of this space -- but if it were super cold and we couldn't get it up to a comfortable temp then we have other options).

I guess another argument for keeping the systems separate, at least in my case, is the low use of zone two means that we could limit our upgrade to only the first zone in the beginning. It may be that we don't really need to upgrade zone two, or at least it's a smaller investment, and we're concentrating on the major energy-consuming unit. This would also give us the benefit of learning and experiencing prior to choosing whether to do HP-only or add the hybrid option in zone 2. OTOH, there's a large opportunity cost lost in not doing both zone at the same time -- a single project vs two, done at different times means have to re-hire work (if not installing myself), complicating tax credits, multiple permits drawn from town, etc.

 

[Chevsky]

Hi Folks, I'm back.
It's been 6 mos since I last asked, and since then I see a lot of installs via YouTube with one ODU and multiple IDU that are dual fuel. I'm trying to spec out at least one system, so I'll have a rough idea of equipment costs as a starting point while I ask for a quotes from installers, which will include labor and other expenses. Looking for a sanity check on brand/design, and whether I'll need new refrig lines or if I can use the existing copper runs.

Q: Can anyone help me with these model numbers and design? (two more questions below)

I'm leaning toward a Diakin Fit hybrid, ducted, propane backup. Models are DZ17VSA601BA (54K BTU HP) with two upflow furnaces DM97MC0804CN and DM97MC0603BN, and two coils. CAPE4860D4 and CAPEA1818B4.

Home is year 2000, heating/cooling zone 5, near Cape Cod, with two completely separate systems. Large space is 2300sf single story, smaller space is 600sf above the garage. Ducts are fiberboard with flex drops.

Old hvac is year 2000, 100K and 75K BTU, and 1.5 + 2.5 ton ACs. If I pick a cold-climate -13F HP, then maybe could forgo one or both furnace backups, and go coil-only/all-electric (tho might not reduce cost any)

Calcs rages from 26K-32K BTU/hr heat load before scale factor (I'm using 1.4) -- so I feel very comfortable with 4-ton for both spaces.

These five major pieces of gear would be $5K, $3.4K, $2.7K, $0.8K, $0.5K respectfully, =$12,400 pre tax/delivery. I like the idea of side-discharge & quiet, so Diakin, Gree, Haier.... vs the cube style. (this is my dream config, so I'll prob scale it back a lot, to maybe half or 2/3 this wholesale price--must make compromises)

Q: Can anyone validate this, or suggest a better alternative design, brands? (like to stick with variable-speed scroll compressor) Maybe specific components and sizes? I know this Daikin Fit 48+ can connect to multiple (≤8) IDUs, but I don't know if this unit has two connections on the base unit, and/or if IDU are tee'd off using a branch box or simple tees.

Q: Can I use the existing 3/4" + 3/8" refrigerant line sets? or will i need to run 7/8" for the bigger IDU?

Q: Does anyone think it's unreasonable for me to shop an installer based on the sytem I've spec'ed?

Thank you!

[[PS, Probably not worth mentioning, because I'll prob have to give in soon or later... I'm ok going with a "non-communicating" system since I use a Radio Thermostat which allows me to use a 3rd party Android thermostat app, which is completely local networking--doesn't use vendor's cloud service.. I'll prob be forced to use their cloud-connected phone app. Would be nice if I can still use a "dumb" style thermostat and app (but my guess is I'll be forced to use cloud due to all the necessary dual-fuel and/or cold-climate settings. Some folks using Gree dual Fuel are using non-cloud EcoBee thermostats)]]

 

[Fitter30]

So who's going to install your system a contractor? A contractor isn't going to give you though prices on the equipment that you have listed and warranty the work. Has someone done a manual j load program on your house? Have you thought about the training it takes to work on vfr variable refrigerant flow equipment and the program to hook up to the equipmenFt? The higher the seer the better trained service person has to be especially if it's in the 20's. A vfr unit has to use their wifi thermostat. Compressor , condenser fan and blower all vary speeds.

 

[WorthFlorida]

I have to agree with Fitter30. This forum get hundreds of queries like yours and the online pricing. Having a good local HVAC is very import just for service and break downs. Most stick to two or three brands that are reliable since they don't want service calls under warranty and the tech are trained on the specific brand. Also, for the install will take some duct work changes. As far as using existing copper new is always better but it gets costly. The contractor usually will know the best route. Using old copper the lines need to be flushed with nitrogen and to expel any oils.

I have to say yours is about the best thought out plan and I like the one compressor for both units. On the heat side you still have two units with gas, cooling your down to one. I understand MA has the highest electric rates in the country.

This forum has a member named Dana and he about seemed to have disappearEd. He is a HVAC designer and had thousands of posts. I believe he lives in CT. At the top of this post there is a search and put in DANA. you can send him a "conversation" which goes to his email. He might be for hire?

 

[Chevsky]

Yes, a contractor will install, and will need to warranty the install. The manufacturer will warranty the equipment AND the labor to correct the equipment failure. Hmm, looking at Daikin's warranty, they don't seem to cover labor when replacing failed equipment. Me no like. Haier on the other hand seem to cover labor. Daikin now has a big presence in North America with their TX plant... so how much does ease in executing a warranty add to price, brand to brand. All these practical differences will affect cost--letting the installer steer the brand choice based on their familiarity vs the system I want, warranty covereage baked into the equip cost, availability of units, availability of installers, etc.
Honestly, I feel the cards are stacked--MassSave requires using one of their certified HPIN installers in order to get the rebate. This severely restricts my choice of installers. My past experiences with locals isn't great, like when my old furnace quit, I got "20 year old furnace? Probably a cracked heat exchanger. I don't need to look at it--we'll swap it out for a like-80% unit for $12K." No thanks (I diagnosed myself; it was a $4 filter-MERV too high, restricting air flow, overheating the single-stage furnace). Finding an honest, fair, independent installer might be incompatible with the MassSave rebate eligibility.
J-load -- I've calculated heat load based on fuel use over four sample periods in the past two years... So it's measured, not estimated. Sizing is less critical than it used to be--new vfr systems are adaptable to WIDE load swings, and run from <30% to 100% call. Choosing a unit isn't a great feat of engineering. I can size a system, and chose it based on application/fit/need, and desired warranty, etc, and if I choose the system then I hope to not pay an equipment markup. I cannot run new linesets, connect lines, adjust duct work--so I'm happy pay for that. (Hell, I'm a contractor too, and I have to budget my expenses and life-overhead out of a modest hourly rate.)

 

[Chevsky]

I'm now considering going full electric--no furnace backup--by using one of the better 18-20 SEER2 heat pumps that are rated down to -13°F. (Fireplace backup!). Maybe still only one outdoor HP with two indoor ducted coils/air-handlers, OR maybe two simple, completely separate units. This depends on the overall cost--seems like when you deviate from the least common denominator the price jumps up--like having a single ODU and two IDUs is viewed as "exotic" or something (again, because location dictates who I can find to perform the install, and they may not be HPIN--one thing or another always seems to disqualify the rebate)

 

[Fitter30]

Delete

 

[John Gayewski]

I'll just add that a heat pump rated for neg 13 degrees probably isn't going to be sufficient for winter. These claims are made from testing In a lab under optimal conditions for the claim. Heat pumps work very well for cooling but heating not as much. If your going with heat pump only you may want another backup beyond a fireplace. Possibly electic baseboard or some in floor heat to help. You could get some gas fireplaces in a couple other spots or something, but the heat pump will likley need help, if you value being comfortable that is. Some people let their house get to 45 or 50 in the winter. That's usually when they call us that their plumbing is freezing though.

 

[Chevsky]

That's what I've been thinking over the last 6 months! But I'm trying to break this conservative idea, and break free of the worry that these latest HPs can't cut it when it's very cold.

www.youtube.com/watch?v=OcwIz6heDss
These folks at Electrify Now, Electrify Maine, Mitsubishi & Daikin are claiming that even in Caribou Maine they can get away with only very rare times that backup kicks in. And I'm near cape Cod, where the coldest temps are much warmer than theirs. I know, it's hard to accept, but just like EV owners are swallowing their range anxiety, I think it's time to risk it and break the dependance on oil. I would also save on not needing to cut in two low-temp exhaust vents, one which would go through the roof. In the worst case I can add up to 20K electric backup element (but wouldn't be supported by my 11KW genny, during outages). If it couldn't keep up, I wonder what the manufacturer would say if quantified that situation in some way--I mean, if I needed to swap out air-handlers for 96%afu furnaces after the fact.

 

[John Gayewski]

That's what I've been thinking over the last 6 months! But I'm trying to break this conservative idea, and break free of the worry that these latest HPs can't cut it when it's very cold.

www.youtube.com/watch?v=OcwIz6heDss
These folks at Electrify Now, Electrify Maine, Mitsubishi & Daikin are claiming that even in Caribou Maine they can get away with only very rare times that backup kicks in. And I'm near cape Cod, where the coldest temps are much warmer than theirs. I know, it's hard to accept, but just like EV owners are swallowing their range anxiety, I think it's time to risk it and break the dependance on oil. I would also save on not needing to cut in two low-temp exhaust vents, one which would go through the roof. In the worst case I can add up to 20K electric backup element (but wouldn't be supported by my 11KW genny, during outages). If it couldn't keep up, I wonder what the manufacturer would say if quantified that situation in some way--I mean, if I needed to swap out air-handlers for 96%afu furnaces after the fact.

I'll be interested in your outcome. Heat pump owners like saving money, but usually admit the house isn't very comfortable. Which can be fine, but I hate a cold house in the winter and blasting more hot dry air is generally makes me feel sick.

 

[WorthFlorida]

I'm now considering going full electric--no furnace backup--by using one of the better 18-20 SEER2 heat pumps that are rated down to -13°F. (Fireplace backup!). Maybe still only one outdoor HP with two indoor ducted coils/air-handlers, OR maybe two simple, completely separate units. This depends on the overall cost--seems like when you deviate from the least common denominator the price jumps up--like having a single ODU and two IDUs is viewed as "exotic" or something (again, because location dictates who I can find to perform the install, and they may not be HPIN--one thing or another always seems to disqualify the rebate)

EPA minimum is Seer 14-15, with a new air handler makes Seer 16. Most manufacturers use generic parts for these units. Once you go above seer 16, thing's really get expensive. One major draw back is each manufacturer has it own proprietary control boards for the air handler and compressor and in some cases the thermostat. Carrier Infinity units are all proprietary. Amazon has the thermostat at $899.

Depending on the air handler, electric heat strips is easily added, 5-kw unit is the norm here in Florida. You will need 30 amp circuit just for the air handler. For a 10 kw you'll need 60 amp circuit. If you want to drop oil, do go with electric heat strips. They are very low cost to add. The once or twice polar express deep freezes, you just may need the electric heat. You might be away on a winter cruise and lightning up the fireplaces? It's why I like WiFi thermostat.

I have a heat pump/ac (3.5 ton cooling). Smart thermostats regulates when the "aux" heat is called for. Outside temp from a local weather report, the set temperature, the actual temperature and the program settings of the thermostat.

Generally, if the set temperature is more than two degrees (programmable) the air temp, the "aux" is called for. Smart thermostats learnwhen the outside temps get too low to handle the heat load, the "aux" is called for. Nest is not the only one that learns. Some thermostats turn the aux heat off when the room temp is within the two degrees or not until it the room reaches the set temperature.

Thermostats can be manual adjusted for aux heat only or both. For heat pump only, remove the program for aux heat. My unit is setup for both but Florida winters are quite mild but those few days in the 40s and 30's the electric heat is called for.

 

[Fitter30]

Fujitsu is the mini that is best on low temp heating by far. All minis lose capacity even the hyper units. Need to look at your coldest temp and btu output of the equipment. Each factory has that info.​

 

[Chevsky]

Arrgh, this is not a simple decision. John G has me doubting all-electric due to slow recovery and high blower volume, inability to crank up when I just feel like it. That I have two spaces/systems makes high performance hard becuz cost gets high so quickly. I have 200 amp service, but there's a limit to using all of it when it's ultra cold. MA has high electric rates too... Now this dicussion has me thinking of non-cold-climate heat pumps with gas backup that kick in sooner (at higher temp). I wish I didn't have two spaces. sigh.

 

[Chevsky]

Maybe I only upgrade the main/large unit this time around.
Here are some questions...

Q: On a 2-zone setup, how are the refrigerant lines branched? In the OD frame, are they just tee'd off such that either or both coil units get hot fluid when their manual (install) valve is open, and the ID calls for it? Is is that simple? Or is each zone solenoid-valved-open when the ID calls for heat? Do all residential HPs that support more than two zones have a separate line set connection pair for every zone? (E.g. would a Gree MULTI42HP230V1EO, which support 5 zones, have 5 line set connection pairs?)

I got clarification on MassSave's rebate -- $10K for whole-home and $1250/ton on partial. I originally read that as if I upgrade ALL my equipment then it's whole-home. But they say that if the new system is hybrid/dual-fuel then the HP is only "part" of heat source--I'll still use gas, so "partial". Since the HP will be 4-ton (may eventually feed two ID units, but initially only the larger), so I'll get $1250 x 4, plus $500 for the integrated control. (Federal will also give me $2000 this year, and then another $2000 when I install the second coil+furnace if/when in a different year.) So will lose $5000 rebate by only upgrading one system. The smaller system is used in summer (10 seer?), but only a little in the winter--I use a small space heater daily in one room off the smaller area, and the furnace only when we use the other room in that space, which is seldom. So I accept this less efficient hvac in this area for another season or two (or forever).

So this means I choose a brand/model that is setup for two zones. This time around it'll be a simple, single dual-fuel system install, in the basement, with only one new low-temp vent cut through the rim joist. Least common denominator job. I can get away with a lower-end cold-climate HP if I'm ok with a switchover point around 10°F, which is only occasional in my locale. (This may also provide hotter forced air when it's very cold--which is perhaps "more comfortable"... meaning, what's being characterized by consumers as "more comfortable", and contrasts the industry's marketing the HP's level, low-latency (and constantly blowing) heat as "more comfortable".)

This brings me to the down side of this method. If I DO upgrade the second/smaller system in the future, then this means a second "job" for my installer. The whole process of permitting, inspections, etc, is repeated, and I'm pretty much going to have to hire the same installer, unlikely not to, unless something went south during the first install. Not doing both the first time will increase the total cost, potentially by a lot. So I guess it depends if I choose to never upgrade other system, and stare at the ugly old ComfortMaker can sitting next to the shinny new HP. ... ok I've talked myself out of this. bad idea. Hmmm, maybe I just mention this idea to the installer before he quotes it, so I firmly put across the notion that I'm serious about saving money--don't bother high-balling my quote.

 

[Fitter30]

Two zone system condenser has two sets of lines coming out of it. With minis power and communication comes from the condenser in three 14 gauge wires. Need to investigate what size indoor units can run from a certain size condenser. There usually close in btu. My case im using two three head minis systems. All have the same btu heads and with at least two on. There is also a 30% tax federal break.

https://www.google.com/aclk?sa=l&ai=DChcSEwjihoXV5_WAAxXSz-MHHWCpAX0YABACGgJ5bQ&gclid=EAIaIQobChMI4oaF1ef1gAMV0s_jBx1gqQF9EAAYAyAAEgKdZPD_BwE&sig=AOD64_3alixyS4EvK79-43RH9Nejyei4Vw&ved=2ahUKEwiz0P3U5_WAAxVRmIkEHTBnCvcQ0Qx6BAgOEAE&adurl=

 

[Chevsky]

30% fed tax credit is capped at $2K per year -- that's why I put in $2k above. Also, there's a $500 per integrated control (one whole system -- 1 heat pump with N# of heads, constitutes one control. So if I did two completely separate systems I'd get 2 x $500), and then HP-water-heater is a separate $, exterior window/door upgrade is another $, insulation, etc. These are under the IRA (Inflation Reduction Act). Some of those other tax credits are collectively capped at $1200, so the IRA program advertises $3200 in credits annually. Some of the other credits are not under the $1200 cap, so total fed IRA tax credit can exceed $3200 per year.
So, if do only the large area system this year, and then the small area next year, I think I qualify for another $2000 for the 2nd head, if it involves a 96%AFU furnace,... or if it's a whole separate system (dual fuel or straight electric w/ HP). If it were only a coil off the first-year-large-space HP then it wouldn't qualify because no HP or other "efficient" equipment is being installed--just an air handler. (IDK, maybe that I'm uninstalling an 80% gas furnace makes it qualify??). Anyhoo, so if doing the job twice--large space 1st year, small space 2nd year--and it does'nt increase the cost overall by hiring somebody twice, then I'd be ahead by getting the extra $2000 because 2nd half of the project occurs in a different calendar year, again if it involves qualifying equipment.... I guess.

PS, late this year (2023) and into next year, these tax credits are being moved into equipment rebates, so they can be knocked off the purchase price. Why I don't like this: Imagine you learn of the $3200 tax credit program. You start your research and learn how much this equipment costs. You begin to think :^/ ₒoO"$1500, with a tax credit it costs me nothing", so you go out and get a quote and it's good.... Only later to find out that it already subtracts the rebate. This is happening with the MassSave $10K rebate on hvac systems, because installers are allowed to "manage" the rebate.