Central HVAC systems vs mini-split?

[CT77]

I recently purchased a new house, and I'm going step by step upgrading what I can afford at the time. My heating is hydronic baseboard powered by a 30 year old peerless boiler burning oil. I have no air conditioning at the moment, nor ductwork. My boiler is insufficient and I've already had to spend a few hundred fixing it, so it's on my short list of things to replace. Right above it is adding air conditioning.

Assuming I need to replace my boiler, I figured I might as well do both at the same time and install the air conditioning and boiler in one go. This leaves me with a few options- do I keep the hydronic baseboard and get a new oil boiler, and add in ductwork for central air? Or go with mini-split for central air? Or replace the oil boiler completely and go with a furnace and ductwork for propane forced air and central air?

My house is built in the late 80's in New England, it's 3000 Sq FT 4 bedrooms, a very rectangular colonial with a walkup attic and open basement, so adding ductwork would probably be easy if I put a unit in the attic and a unit in the basement.

I love certain things about baseboard hydronic, and I hate certain things about it, so I'm neutral. Any suggestions? Thanks in advance.

 

[Dana]

First things first- run an aggressive (not conservative) room by room load calculation using Manual-J type methodology or similar. Make all of your assumptions about R-values and air tightness skew to the tightest and highest-R that is "reasonable" given the construction or it will overestimate by too large a factor, which will be bad for both efficiency and comfort. To get a pretty good ball-park on it you can use freebie online Manual-J tools such as LoadCalc, but set the infiltration levels to ZERO or it will lead to sub-optimal oversizing factors.

If you had the place through the winter, use K-factor on (wintertime only) fill ups or exact dates and amounts to measure the heat load using the Peerless as the measuring instrument. The methodology for doing that is explained in this bit o' bloggery.

The heating and cooling loads of individual bedrooms are usually much lower than the output of even the smallest mini-split heads, and going completely ductless with a "head in every room" is TERRIBLE for efficiency, and often for comfort. Even when a head in a low load room is nominally "off", with multi-zone ductless there will be refrigerant flowing in the coils whenever ANY other zone is running, which can lead to overheating/overcooling those rooms. Splitting the output of a mini-duct cassette between 2-4 rooms is usually a more efficient and more comfortable option. But without the individual room load numbers it's impossible to sort this stuff out.

Before spending big money on it, spend $500-1K having a professional engineer or RESNET rater- somebody who makes their living and reputation on the accuracy of their numbers (and not an HVAC installer) run those numbers, but sanity check the whole-house load against fuel use. It should be within 15% if the fuel use was wintertime only. (Solar gains and idling losses skew the numbers pretty badly in the fall and spring shoulder seasons.)

Every oil boiler out there is likely to be 2x or more oversized for the load of a 3000' house, but with a heat purging economizer control (standard on many but not all new oil boilers) the efficiency hit from the low low duty cycle during the shoulder seasons isn't too terrible. As long as it hasn't been chopped up into many small zones it can still work efficiently. Micro-zoning can be problematic, even for cast iron boilers. Some napkin-math on that lives here.

Sizing an electric boiler correctly for the load is possible, and would allow you to even undersize the ductless a bit since you would have 100% "Hail Mary" backup to manage peak heating loads during Polar Vortex disturbance events.

Putting air conditioning & heating ducts in an unconditioned attic is a terrible idea on several accounts. The worst thing you can do for comfort and efficiency to a multi story house at New England wintertime temperatures it start punching holes in the top of the pressure boundary of the house, maximizing the amount of stack effect driven infiltration, and creating cold drafts when the ducts aren't actively heating.

The importance of right-sizing for comfort can't be overstressed. A 3x oversized air conditioner or furnace/heat pump can heat/cool the place, but it's the opposite of comfort- the hot blast followed by the extended chill in winter during colder weather, and insufficient dehumidification in summer. For multi-split ductless oversizing the compressor capacity by more than 1.25x for the heating load at the 99% outside design temperature results in a steepening decline in average efficiency (for single-zone mini-splits that can be bumped to about 1.5x, due to the generally bigger turn down ratios.)

The typical reasonably tight 2x6/R19 type 3000' house with clear-glass double-panes (no low-E) in CT would come in at about 2 tons of cooling, and 35-40,000 BTU/hr of heating. Most cold climate (aka "hyper heating") minisplits/multi splits would need only 2.5-3 tons of compressor to manage that much load- not be ridiculously oversized for the cooling load, and right-sized for the heating load. It's rare to find a house that size that would run more efficiently (or more comfortably) with 4 tons, but sometimes zoning issues demand more heads than a 3 tonner would supply. It's likely that the first floor could run on a single 1 ton-1.5 ton ducted Fujitsu xxRLFCD series mini-split, or one or two 3/4 ton heads/cassettes, depending on layout. (Room by room load numbers are essential for making this call.) If the second floor is all doored-off bedrooms and a bathroom (or two) a bit more thought and creativity needs to go into it, but it's usually do-able without the crazy "every room it's own zone" approach that inevitably leads to crazy oversizing with ductless systems.

 

[Sponsor]

 

[Dana]

BTW: Whether it's going to be finished into living space or not, if the foundation isn't insulated it represents a significant fraction of your space heating load. The idling and distribution losses of the boiler to the basement might keep it from freezing, but even at 50F in the basement the losses are large. Insulating the foundation walls to the current IRC code minimum of R15 continuous insulation (no studs) performance level is recommended, and should be included on any of your Manual-J load calculations.

 

[CT77]

Dana, you've given me a lot to think about, thank you very much for the detailed response. I don't know that I can use oil usage on my boiler to determine load since my boiler wasn't sufficiently heating a few parts of my house when the weather dropped to freezing (HVAC tech didn't seem interested in diagnosing, said it was probably at the end of the water line and suggested getting a new boiler). I never thought about the side effects of running duct work into an unconditioned attic since most of the houses I've owned/lived in have had a unit in the attic that cooled the 2nd floor. Here are my concerns with what you've said:

1) I'm willing to pay someone to do a manual J and D, the problem is finding someone. Every HVAC engineer I've found only works on huge commercial projects, I'm not sure I can find someone that would do a small residential one. I find a lot of companies that you can mail your info to and they will do it, but that can't be a good way to do it. I'll keep looking because I think this is a great recommendation and it's not something I trust myself to do correctly.

2) If running ductwork down from attic to 2nd floor is a bad idea (even if insulated?), that would completely negate central air conditioning as I don't want to deal with the headache of running ducts from the basement to the 2nd floor and losing closet space in my finished closets.

3) I'm concerned mini-splits will hurt the resale value of my property and create warm/cool zones when doors are closed. In my area at least, nobody puts mini-splits into homes this size/value. I know the opinion is wrong, but they are viewed as the cheap and ugly way to put A/C into your house and it will definitely turn people away if we ever sell. I know they make cassettes and other options, but you're also running a huge pipe along the length of your house outside to the compressor, no matter how nicely you hide it it is noticeable. Also, most of my family has mini-splits and they love them except when the doors are closed. Our bedroom doors are always closed.

4) That's a great recommendation on the insulation on the interior foundation, I looked and the DoE does recommend it. I'll price out rigid for the application, thanks.

 

[Dana]

There are several companies in southern New England trading in reclaimed roofing foam board at very steep discounts (typical priced at 20-35% of virgin stock foam). It takes 3" of 2lb roofing polyiso to hit the IRC's R15 continuous insulation minimum, but if you're building a studwall you can get there on a U-factor basis with 1" of foil faced polyiso trapped to the foundation with a 2x4/R13 wall without creating a mold farm. While a 2x6/R19 wall would meet the IRC's thermal performance requirements, it's risky from a moisture/mold point of view.

Of companies that do Manual-J/D remotely, I've reviewed a couple of Manual-Js performed by a company in Georgia called Energy Vanguard that looked right, even on an antique building in Cambridge MA with many non-standard construction aspects. I've never dealt with them directly, but getting their attention seems to be the hardest part when they're busy.

Even insulated duct in an attic is bad ideal. The conducted heat losses through R8 duct is small potatoes compared to the extra air leakage (from air handler driven pressure differences) and the inevitable cold drafts in winter spilling out of the registers in winter. There is a reason why a code min attic is R49, and not R8.

A single mini-ducted Fujitsu xxRLFCD can be mounted vertically and eat up only 6-7 square feet of floor area, and ducts can be run below ceiling level in soffits. Soffited duct runs are not cheap, but they can be reasonably aesthetic, and can be used for other purposes too (wall wash down-lighting, etc.) This installation is a 1.5 ton -18RFLCD retrofit heating/cooling a house in Berkeley CA:

This installation was used somewhat bulk flex duct which takes up more headroom that a 4" x 24" hard-piped duct. The grille is the common return (unducted), just below the cassette. If going with a common return like that it may be necessary to use partition wall cavities as "jump ducts" to get adequate flow when the bedroom doors are closed.

This set of slides is from a recent presentation delivered at the North American Passive House Conference in Boston by a company in Virginia that regularly uses ducted mini-splits as whole-house heating & cooling solutions on higher performance houses, with several good design tips. You don't need to live in a high-R house to use ducted minisplits effectively, but on "normal" houses it takes more than one to do the whole house. One per floor usually works for 2 story colonials. The RLFCD mini-duct cassettes are only good to about 0.4" water column static pressure, about half what "full sized" AC/furnace air handlers are designed for, but Fujitsu recently released a series good for 0.8" w.c..

Mitsubishi's commercial PEAD series mini-duct cassettes area also good for 0.4", but have less modulation range (and are more expensive) than the Fujitsus. Mitsubishi's SEZ-KD residential mini-duct cassettes are too wimpy (0.2" ) to do a whole floor with a single cassette. Daikin has the same issue.

 

[Reach4]

Are there systems that share a compressor and have you tee insulated Freon to more than one ductless ceiling cassette?

I know they make cassettes and other options, but you're also running a huge pipe along the length of your house outside to the compressor, no matter how nicely you hide it it is noticeable.

How "huge" are you picturing? How about an extra compressor outside, with landscaping around it, feeding a ceiling cassette?

 

[Dana]

Are there systems that share a compressor and have you tee insulated Freon to more than one ductless ceiling cassette?

How "huge" are you picturing? How about an extra compressor outside, with landscaping around it, feeding a ceiling cassette?

I think he's talking about the 3.5-4" lineset conduits :

Not exactly a thing of beauty, eh? (But then again, neither are gutters & downspouts.)

If you really find the look objectionable (they tend to look like crap against brick, for sure), there is always a way to avoid outdoor lineset conduit.

If you get rid of the oil burner it's possible to repurpose the flue chase for running things like ducts and linesets indoors. On a 3 story project I was involved with a handful of years ago there were 3 wall hung compressors (one per floor), but the line sets were are run internally, using the chimney chase (after the masonry chimney was removed) and floor joists for running the line sets, no vertical or horizontal runs on the exterior of the house. Similarly on a co-worker's 2 story house with 3 compressors the vertical linesets between floors were run indoors adjacent to the (formerly exposed) steam heating system plumbing, which he then opted to enclose.

Running linesets in the attic are far less of a problem than running ducts in the attic- the pressure boundary penetration at the ceiling is small, and there is no potential for air handler driven infiltration from duct leaks.

 

[CT77]

I think he's talking about the 3.5-4" lineset conduits :

Not exactly a thing of beauty, eh? (But then again, neither are gutters & downspouts.)

If you really find the look objectionable (they tend to look like crap against brick, for sure), there is always a way to avoid outdoor lineset conduit.

If you get rid of the oil burner it's possible to repurpose the flue chase for running things like ducts and linesets indoors. On a 3 story project I was involved with a handful of years ago there were 3 wall hung compressors (one per floor), but the line sets were are run internally, using the chimney chase (after the masonry chimney was removed) and floor joists for running the line sets, no vertical or horizontal runs on the exterior of the house. Similarly on a co-worker's 2 story house with 3 compressors the vertical linesets between floors were run indoors adjacent to the (formerly exposed) steam heating system plumbing, which he then opted to enclose.

Running linesets in the attic are far less of a problem than running ducts in the attic- the pressure boundary penetration at the ceiling is small, and there is no potential for air handler driven infiltration from duct leaks.

Yes, that's what I'm referring to. I have a very dark colored house and those lineset covers would be 2x as noticeable as in that picture. I'd love to get rid of the oil burner, but what would heat my home? I don't know that I can trust a heat pump to heat to even the rare -5 to -15 we have in CT. Are you a believer in Fujitsu over Mitsu for mini-splits? Also as an aside, I thought flex-duct was widely frowned upon by HVAC professionals compared to metal ductwork?

 

[Dana]

Yes, that's what I'm referring to. I have a very dark colored house and those lineset covers would be 2x as noticeable as in that picture. I'd love to get rid of the oil burner, but what would heat my home? I don't know that I can trust a heat pump to heat to even the rare -5 to -15 we have in CT. Are you a believer in Fujitsu over Mitsu for mini-splits? Also as an aside, I thought flex-duct was widely frowned upon by HVAC professionals compared to metal ductwork?

Lineset covers come in colors other than "titanium white", but it's not the full graphic designer's color palette.

For ducted mini-splits I favor Fujitsu for a number of reasons, not the least of which is that they can be mounted horizontally or vertically, and have less stringent static pressure constraints. But I'm a big fan of Mitubishi's FH series ductless mini-splits too.

Yes flex ducts suck, even though that outfit in the Bay Area knows how to deal with them, I much prefer hard piping.

There are plenty of cold climate heat pumps with specified output at -5F (like the Fujitsu RLFCDs, for instance) and several rated at -25C/-13F or colder, but you should really be looking at the load at your 99% outside design temperature or you'll sub-optimally oversize the heat pump. The Northeast Energy Efficiency Partnerships (NEEP) maintains a list of heat pumps suitable for your climate (or colder), along with their efficiency ratings an the minimum/maximum output at +5F, as well as the ARHI test temperatures of +17F & +47F . When you know the whole house load (or floor by floor load) you can use the "Heating Capacity (Max Btu/hr @5℉)" slider on the upper right corner of this page to narrow it down a bit. Most bigger deal ducted heat pumps have auxiliary resistance heating strip options to cover the shortfall at the Polar Vortex extremes, most mini-splits do not. If going with a multi-split or modulating bigger air handler system (like the Carrier Infinity GreenSpeed) don't oversize the heat pump by more than 1.25x for the heating load, but for single zone mini-splits you can push that to 1.5x oversize factor, due to their higher turn down ratios.

Most 3000' 2x4 framed houses in CT with at least some decent storm windows could be heated & cooled by 3 tons of cold climate heat pump after a bit of air sealing, and insulating the foundation.

The Fujitsu RLFCD series aren't listed by NEEP, since they don't have a pan heater for automatically managing defrost ice, a problem that would be extremely rare in CT, but could be a real issue in northern VT, but they use the same cold-climate vapor injection compressor technology. That series has a control output to call up auxiliary heat, but won't power the aux heat the way bigger-air handler heat pumps do. Simply up-sizing usually works with that series- there are people heating high-R houses in northern MN with RFLCDs without pan heaters at temps that hit the -20s. They still put out heat, but the capacity and efficiency isn't specified below -5F. The -18RLFCD still puts out 18,400 BTU/hr @ -5F, or 19,700 BTU/hr @ +5F. A pair of them would have sufficient capacity heat my sub-code 1920s antique 2400' bungalow in Worcester MA just fine. I suspect your design heat load is lower than mine due to higher R values and better windows, possibly a slightly higher 99% design temp. Their recently released beefier air handler RLGX cassette series comes in even bigger flavors- up to 4 tons if need be, but their heating capacities per ton are somewhat lower than the RLFCD series. Still, a 3 ton ARU36RGLX puts out about 30,000 BTU/hr @ -5F, 33,000 BTU/hr & +5F.

 

[Reach4]

I think he's talking about the 3.5-4" lineset conduits :
Not exactly a thing of beauty, eh? (But then again, neither are gutters & downspouts.)

Got it.
Beauty can be subjective.

Lineset covers come in colors other than "titanium white", but it's not the full graphic designer's color palette.

PVC and many other materials can be painted.

 

[CT77]

Thank you again Dana, you've given me a lot to think about and a starting point- I'm going to either find someone to run a Manual J/D or do it over the web if I have to. I'm also going to insulate my basement interior foundation walls. I'm still not sure I'm sold on mini-split, but I will be contacting a few companies to see what they have to say when they come out for a quote.

 

[Dana]

Thank you again Dana, you've given me a lot to think about and a starting point- I'm going to either find someone to run a Manual J/D or do it over the web if I have to. I'm also going to insulate my basement interior foundation walls. I'm still not sure I'm sold on mini-split, but I will be contacting a few companies to see what they have to say when they come out for a quote.

I've found that it's better to tell THEM what you want than to sit back and let them come up with proposals. Asking about what they would do for a mini-ducted solution vs. multi-splits, and letting them know that you're trying to limit the oversize factor, and want to keep the ducts inside the thermal envelope might result in more relevant proposals. It's a waste of everyone's time to just let them take a WAG at it and cook up proposals that ultimately make no sense.

 

[CT77]

That's definitely my plan Dana. I'm assuming the Manual J and D I get will tell me, more or less, what equipment I need and what kind of ductwork design I'm looking at for either type of system. Then it's just a matter of pricing out the difference between all the options. Before I read what you said, I never imagined a heat pump in CT was a viable solution, but in doing some research it appears almost like a misinformation campaign is out there spreading false information on them.

 

[Dana]

research

That's definitely my plan Dana. I'm assuming the Manual J and D I get will tell me, more or less, what equipment I need and what kind of ductwork design I'm looking at for either type of system. Then it's just a matter of pricing out the difference between all the options. Before I read what you said, I never imagined a heat pump in CT was a viable solution, but in doing some research it appears almost like a misinformation campaign is out there spreading false information on them.

Nate Adams of Energy Smart Home Performance almost always specifies right-sized (usually modulating) heat pumps as part of the retrofits for fixing comfort complaints, whether the house is 10 years old or 110 years old, 1000 square feet or 5000 square feet. His pet peeve regarding the HVAC industry is how often he has to tell clients their brand-new ridiculously oversized equipment is a major part of the problem, and has to go in order to make the house reasonably comfortable. Nate is a big fan of Carrier Infinity Greenspeed heat pump systems which are on the higher-end of the price (and price/performance) scale, and an anti-fan of ductless solutions, but I suspect he's never really worked with what's out there for single zoned ducted mini-splits, which are smaller/cheaper with bigger modulation ranges. There is a lot of media on his Nate the House Whisperer blog explaining comfort issues relative to sizing (as well as a few books to sell). They are located in Cleveland, where the 99% outside design temp is +6F (the same design temp as Hartford, but with deeper dips in temperature than Connecticut during Polar Vortex disturbance events). He also documents several comfort retrofit case studies of his projects with varying degrees of detail- usually lots of pictures.

The Greenspeed systems almost have too many design features to program. Some of the "gotcha" features on as-used efficiency are reheat, where they turn on some auxiliary resistance heat (usually not needed for comfort) during defrost, and the outdoor lockout temperature for the aux heat, which if set too high burns a lot of power when the heat pump can still handle the load. Screwing up those settings can increase power use by 30% or more with no comfort benefit. Trane , Lennox et al have similarly complex control programming to set up/screw up on their modulating systems, most of which only have a 2:1 to 2.5:1 turn down ratio, a much lower modulation range than the better mini-duct cassettes.

I recently learned that Carrier is putting their name (also Bryant) on 1.5 ton Midea mini duct systems ( pretty good units from China), but it's not clear if Carrier is they're also OEM-ing Midea' s top-shelf stuff. Midea's cold climate 2-tonner using Toshiba's cold climate compressor technology is pretty good, with more than a 4:1 turn down and excellent HSPF/SEER numbers. The 1.5 ton & bigger Midea cassettes are also flow rated at 6.5 water inches, which can drive some significant duct systems. Unfortunately local distribution & support is pretty limited on them right now, but may be better in the future. Carrier also sells Toshiba's mini-ducted systems, but they make it impossible to get any data on them from the web.

You don't say where you are in CT, but in Norwalk, Steven Winter Associates ( 61 Washington St. Norwalk, CT 06854 203‐857‐0200 ) might be able to refer you to a reliable local Manual-J/S/D source, if they don't offer those services themselves for houses your size.

 

[CT77]

You don't say where you are in CT, but in Norwalk, Steven Winter Associates ( 61 Washington St. Norwalk, CT 06854 203‐857‐0200 ) might be able to refer you to a reliable local Manual-J/S/D source, if they don't offer those services themselves for houses your size.

Dana, on your advice, I started exploring Heat Pump options with a few different companies. I couldn't get a single engineer to do an independent heatload calc for me, but most of the companies that came sort of did one. One contractor said a heat pump won't work in CT, obviously not going with them. This is the breakdown of the HVAC contractors:

Company 1: Spent an hour measuring and drawing a floorplan, said he was going to do a quicker "mini manual J". Said I had 2x6 construction (I do). Said the addition alone needed 15k BTU of heating. These were his 2 proposals:

1) MXZ-8C48NAHZ, paired with 2x MVZ-A24AA7 (1 in basement with ductwork and supply/returns to 1st floor, 1 in attic with ductwork supply/returns to 2nd floor). The addition would need it's own unit MUFZ-KJ15NA+MFZ-KJ15NA for just the addition. Total cost: 34k.
2) BVA60WN1M18 and BOVA60HN1M18M, in basement, ducted to 1st floor, trunk running to attic and ducted for 2nd floor. Total cost: 22k


Company 2: Spent an hour and a half measuring and drawing a floorplan, said he was going to do a full manual J and it would take time. Said I had 2x4 construction (I don't). This guy was very thorough, and besides being wrong on the 2x4 part, had some good ideas. His proposal:

1) MXZ-5C42NAHZ with 5 heads, 2 downstairs (1 MSZ-FH18NA in addition 1 MSZ-FH12 NAin living room) and 3 MSZ-FH06NA upstairs. Total cost: 20k

Company 3: Spent 30 minutes measuring windows, said he would use floorplan online to do other measurements of rooms. Said I had 2x6 construction. Haven't heard from him on a quote, almost 2 weeks.

Company 4: Spent 30 minutes measuring rooms and drawing a floorplan. Said I had 2x6 construction. Called back saying the amount of BTU's I needed was above what a 1 on 1 Mitsu Hyper Heat could handle, and even multiple units wouldn't work (not sure why?), so he couldn't even do it if I wanted to. He said my upstairs needed 27k BTU, my addition needed 25k BTU, and the rest of my downstairs needed 35k BTU.

Company 5: In and out in 15 minutes, said it would be an easy job, no measurements taken, card thrown in the garbage and not considering.

Basically, my heatload calcs seem to vary wildly from one contractor to another, as do the quotes. What would you do in this situation? I need to buy you a beer for all your great advice when this over, thanks.

 

[Dana]

What would you do in this situation?

I'd run my own I=B=R type heat load, using a computer spreadsheet tool, as well as a loadcalc. Use the most aggressive assumptions possible on air-tightness of both the house and ducts- basically assume it's a hermetically sealed house with only heat recovery ventilation to be able to breathe. The defaults on air leakage in most load tools are ridiculously conservative, and it shows up as excess load that isn't really there. The loadcalc will come in higher than the IBR, but it will bracket a range. If you do it room-by-room you'll be able to make reasonable decisions on zoning, etc.

If you wanted to punt on it and use a crummy rule of thumb, reasonably tight 2x6 /R19 construction comes in at about 12-15 BTU/hr per square foot @ +5F (central CT type outside design temp), with a few outliers in either direction. So a typical 3000' house would need something like 36,000-45,000 BTU/hr of HEATING capacity at +5F. (Cold climate heat pumps put out more heating BTU @ +5F than their AHRI cooling rating.)

Company 1:

The MXZ-8C48NAHZ, with mixed ducted/ductless zones has 54,000 BTU/hr of capacity @ +5F. If your actual load is 45K that's not crazy oversizing (if it's running the whole thing), but if it's 36K it's too much. Putting ducts in the attic above the insulation and punching holes in the pressure boundary of the house adds parasitic load. It might work, but it's not the right thing to do. Only if the attic is insulated and air sealed at the roof deck would that proposal make any sense at all. For the kind of money they are talking it's worth spending the first 10 grand on air sealing and insulation to bring the loads down.

The MFZ-KJ15NA is good for 18,000 BTU/hr @ +5F.

The 5 ton Bosch in the basement is just plain ludicrous, and isn't even a cold-climate version.

Company 2:

The MXZ-5C42NAHZ can deliver 48,000 BTU/hr @ +5F, and is probably much closer to your real loads. Whether it's right sized on the zone by zone capacities is hard to say. You can look up the capacities of individual heads/cassettes by looking at their AHRI submittal sheets (note- their heating capacity is different on multi-zoned systems compared to single zone, so pull the right sheet) , and check that against your own load calculation.

eg: The FH18NA running on a multi-zone is good for 20K, at any outdoor temperature as long as the compressor has suffcient capacity at that temp. But on a single zone system it's good for about 21K. To find AHRI submittal sheets and design manuals for Mitsubishi equipment, start surfing here.

'With load numbers in hand, it's worth searching the NEEP database for information on heat pumps here.

Company 4 Either doesn't know how do heat loads, doesn't want the job, and isn't worth chasing.

So it's really up to you to calculate the loads. Be aggressive rather than conservative and it won't be insanely oversized.

HVAC contractors don't really have time to do proper calculations when coming up with proposals, but it's well worth YOUR time do run some of those numbers. If you have the spreadsheet numbers in front of you most decent contractors will at least take some feedback on how it might need to be changed a bit and come back with an adjusted proposals. Early summer is usually their busy season due to the air conditioning demand, so availability & attention will be low, and quotes higher than what they will be in the October/November time frame.

Do NOT agree to put ducts in the attic above the insulation. That's easy for the contractor to install, but never the right thing to do (especially at CT style electricity rates.)

 

[Makemenuconfig]

Are there systems that share a compressor and have you tee insulated Freon to more than one ductless ceiling cassette?

They definitely do make this. Sorry I'm late to the party, but on the off chance this helps you or somebody else figured I'd chime in.

Some (but not all) of the outdoor Mitsubishi "HyperHeat" condensers have a large 3/8", 5/8" lines which run into a branch box located inside and can run to the units inside from there. For example this 48,000 BTUH condenser has this feature. But you still have to pay for a branch box. It can reduce your overall lineset lengths/costs. But keep in mind the units don't come charged for *any* lineset so you generally need to add quite a bit of refrigerant.

Diagram from the manual:

 

[Fitter30]

Mini splits have some advantages. Quiet, zoned and energy efficient. The disadvantages indoor units are hard to clean(look at youtube videos), filters are thin, parts might not be readily available and the biggest problem finding a company that has someone that has experience in servicing them. Two systems are in my house both 2 ton with three indoor units. Used two systems for one reason in case a system failed I'd still have heating or cooling till parts came in. Some electric companies offer a energy audit that includes a blower door test it shows how tight the house is.

 

[sajesak]

I recently purchased a new house, and I'm going step by step upgrading what I can afford at the time. My heating is hydronic baseboard powered by a 30 year old peerless boiler burning oil. I have no air conditioning at the moment, nor ductwork. My boiler is insufficient and I've already had to spend a few hundred fixing it, so it's on my short list of things to replace. Right above it is adding air conditioning.

Assuming I need to replace my boiler, I figured I might as well do both at the same time and install the air conditioning and boiler in one go. This leaves me with a few options- do I keep the hydronic baseboard and get a new oil boiler, and add in ductwork for central air? Or go with mini-split for central air? Or replace the oil boiler completely and go with a furnace and ductwork for propane forced air and central air?

My house is built in the late 80's in New England, it's 3000 Sq FT 4 bedrooms, a very rectangular colonial with a walkup attic and open basement, so adding ductwork would probably be easy if I put a unit in the attic and a unit in the basement.

I love certain things about baseboard hydronic Air Conditioners USA, and I hate certain things about it, so I'm neutral. Any suggestions? Thanks in advance.

Hey I am looking for purchase a good minisplit system and is easy for myself to set up with no HVAC. Does anyone have a good suggestion, looking to spend up to 2400. I wanted one with a hepa filter intake for air just to make everything extremely clean.

If not a minisplit unit I was considering getting ice boxes but I think minisplit would be easier...

Thanks and let me know any suggestions and if it is actually worth it.

I have a DIY AC unit box with my 15000btu window AC, it works good but it leaks air (minimally) and allows dust into the room so I want to try something new.

 

[Fitter30]

What u to look at cleaning wall mounted indoor units on utube. Some brands are better than others. Window units that windows close down to 3" might be something to look into.Midea makes them.