Best 18+ Seer Value

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rpfutrell

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So I'm trying to decide on a full replacement of our Central AC and have obtained the quotes below...any guidance from the experts or people in the trade would be greatly appreciated.

I don't want to overspend if it's not worth it. We should be here for at least 20 years is the plan might eventually install solar panels too. So what I am hoping you experts or people in the trades can help me with is ...

  • Guide me on what would be the better value vs. the better product, money aside, to help guide me in my decision.
  • Tips or suggestions on how I might be able to negotiate a better price on any of these units or other models, I'm all eyes and ears here!!
  • How does one calculate, based on the products and information below, the expected payback/ROI? This is more my curiosity than a deciding factor, no??
Thanks in advance!!

Home Info:
Built: 1997
Type: 2 Story Colonial w/ basement
Sqft: 3300 / 2888 heated/cool (rought estimate)
Current System: Electric 1 zone, no ductwork in basement :(
Family Size: 4 total, 2 adults 2 younger children under 5

Quotes: rebates might not be currently accurate

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Past year usage ....

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Nukeman

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What do you use for heat? A heat pump could be added for a small additional cost and give an additional heating source option.

First thing is you need to figure out the size. It looks like you have 3 ton, 4 ton, and 5 ton condensers listed. There is a process called 'Manual J' that can give the size needed and the heating/cooling load per room/floor/zone. A proper Manual J takes some time, but is worth having done (even if you have to pay for it). Many contractors will oversize the unit or just simply use one the same size that is already there. This causes short cycling and poor humidity removal, in addition to additional duct noise from the increased airflow. The ducts also need to be sized for the load. If they were designed for a 3 ton system, you will have problems if you try to use a 4 or 5 ton system with the existing ducts. It is likely that 3 ton is the max you need and probably even smaller would do the job. I have a similar sized house in central VA. It is much older (45 years old) with single pane windows, etc. I have a 3 ton York (2 stage, 17.5 SEER) and it does the job fine. It is also a very quiet.

Start with getting the proper size and then pick the unit. Any of those brands will be fine. With the fairly low cooling loads in Mass., it may be hard to get a payback on the high SEER systems. It will depend some on your exact location, electric rates, and how much it is used for humidity removal in the "shoulder" seasons. Something like a 15 SEER might end up having the best ROI.

The basement space usually represents a very small cooling load. It could be worth adding an additional return in the basement to help to remove humidity.

If you can zone the main and upper floors, it can be nice to have (our house is that way). It can be difficult to do after the hose is built, though.
 

Dana

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A typical ~3000' home in MA would have a cooling load less than 3 tons, but without running the load numbers it's hard to know for sure. You load could be as low as 1.5 tons, or as high as 4 tons if you have a lot of west facing window, but the 5 ton system is almost certainly going to be a mistake.

An office-mate of mine recently had three ductless mini-splits installed (a pair of 1-tonners and a 3/4 ton) in his home in Arlington, MA for about $11-12K, which will be about $9K after MA rebates. It's substantially oversized for the cooling load- he got them for space heating, as a cheaper solution than the pre-existing oil fired steam system, but should be able to cover his heat load with margin. During the cooling season the 1-ton unit upstairs is running near it's max modulation all after noon but it keeps up. The 3/4 ton unit in the kitchen almost never runs, and the 1-ton in the living/dining area cycles on/off at it's minimum modulation. We didn't run the numbers on his cooling loads but from the system behavior it's clear that his cooling load is less than 1.5 tons, for a ~2000' 1920s antique 2x4-framed bungalow w/ R50 cellulose in the attic, dense-packed cellulose in walls, and no foundation insulation. It's not super-tight either- it blower door tested at ~7ACH/50, which means the latent loads are a bit higher than they would be on a tighter house.

It's a lot harder to glean peak cooling load out of billing data than it is with peak heating load in this climate. But on a hot sunny afternoon when the cooling load is peaking you can figure it out by measuring the duty-cycle of your existing unit and working backwards. eg. say it's a muggy sunny 85F day (the 1% outside design temps in MA are in the mid-80s), and say the compressor on your AC is running 30 minutes per hour, the cooling load is then 1/2 of it's rated size. If it's running 45 minutes/hr the design load is about 3/4 of the size. Ideally it would be running continuously for a couple of hours and just barely holding ground, in which case it's perfectly right-sized.

It almost never "pays" to replace a functional AC system, especially in this climate where the cooling season is fairly short and the loads are fairly modest. But if you're going to do it, right-sizing it will provide more comfort. If you're willing to spring for a multi-stage or modulating unit it'll run quieter & longer too.

The up-charge for a heat pump version of a standard split-system isn't very much, but a heat pump that would actually cover your load at 0-10F will be considerably oversized for your cooling load, and at MA-style 20-25 cents/kwh winter retail electric rates and $1-1.25/therm would not be cheaper than heating with condensing natural gas except during the warmer weather (45F+). Still if you right-size it for AC it's still worth the few hundred for having the option to run it in heating mode. But it's not worth paying for the resistance-heating strip backup that is typically an option in those systems unless you're making it your primary heating source. Some of the fully variable ducted split systems like the Carrier GreenSpeed come close to the heating & cooling efficiency if mini-splits, but capacity falls fast below 20F, and I suspect it's a lot more expensive than $10K. If you're on the gas-grid and have a gas-fired heating system in almost all cases it'll be cheaper to heat with gas than ANY ducted heat pump, the rare exceptions being best-in-class mini-splits optimally sized for the heating load.
 

Dana

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Given that the contractors' Manual-Js overshot the heat load numbers by more than 12,000 BTU/hr , it wouldn't surprise me if they similarly oversized the AC, starting with the fact that they're both using an 88F dry-bulb for the 1% design temp, whereas most locations near the coast such as Fall River have 1% design temps in the ~85F range. Weymouth's 1% outside design temp is 87F, so maybe... One of them used 73F for the indoor design temp, which is on the cool side.

So yes, per the load calculation 3 tons would be plenty, even though 2- 2.5 tons would probably cover it, and would run longer cycles, delivering drier air. Anything bigger than 3 tons would provide LESS comfort.

I suspect the pinky on the scale in their heat load calculations are higher-than-reality infiltration numbers and floor losses. Does this house have any foundation wall or slab insulation? How cold does the basement get when you don't actively heat it?
 

rpfutrell

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Thanks so much guys, I can't tell you how appreciative I am for your feedback!

Ok, some of additional info from my wants and needs to AC are:

Yes I'm the same guy replacing my boiler+HW system too, and the design info that can be used can be seen on this thread. Every thing I'm doing is living through a heartbeat to drive efficiency and value, so I greatly appreciate your feedback.

Other Notes of Interest:

Personally: I'm very hot natured. I use to work as a meat cutter for 12+ years. I think something is off with my internal clock, or it could be that I'm covered in hair! :eek:... TMI, I know :) That being said, please skew my needs towards one that cannot live without A/C. Being that I am from the south, I used AC on a regular basis. I don't know how some of the New England (born and raised) people do it. When house hunting in this area, I qwas amazed at the homes that either don't have one, or people that standby the fact they don't need one at all!

So for me, it's ok in April / May and probably even October to November, but June through September I'd rather NOT be without Central A/C running and need something for "comfort" on the edges of the season.

Other info:
All units quoted above are 3 Tons ----> Do I need 3 Tons? I don't understand how this math works either and could use some education.
My current system is a CK60-1C which I believe is 3 ton, coupled with a 5 ton blower. This is all builder quality grade stuff! and that is not a complement.
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Home was built in 1997,and from what I gather is pretty good with insulation. Some the contractors point out that MassSave had been there easily and other than the R4 flex duct, insulation was pretty good.
My understanding is the duct system is going to either break or make any new systems efficiency. I also have two registers that are not blowing any air. So they are either not attached at all, or they are just for decoration?

Given that the contractors' Manual-Js overshot the heat load numbers by more than 12,000 BTU/hr , it wouldn't surprise me if they similarly oversized the AC,
To be fair and not sure if it matters, but the neither contractor was ever privy to my usage for their calculations.

Does this house have any foundation wall or slab insulation? How cold does the basement get when you don't actively heat it?
Home is a concrete basement is about all I know... It doesn't get terribly cold in the winter, It's not necessarily 2X6 construction either, I believe that came a few years later as it relates to code specs for a house around here. However the basement does get fairly hot in the mid to late summer. This is attributed in some part to the dehumidifier running non-stop. This tends to make it a little warmer at times. The basement does not currently have any duct work present, so I can only imagine it would make sense to implement a ductless system here, but not really focusing on that. However it now makes me ponder, how could incorporate something ductless now, with the impending condenser purchase I'm considering? Possibilities?? While there is no duct work present, basement location provides easy access to the current condenser and electrical panel.

However my main focus is on the 1st / 2nd floor for the new system, unless I can be enlightened by you fella's (and ladies if there are any here).

Another one of my wants is take this to a 2 Zone system by using the existing ductwork, and implementing motorized dampers and a maybe even a whole house air cleaner (family members have allergies)

Another thing I'm trying to do is make sure all the current flex duct is upgraded from R-4 to R-8
Also the return design of my current system is disfunctional meaning it doesn't have a filter which as lead the current system to a early failure and innefficiency.

Another question I have is ... Can a line-set be flushed and reused? Is it completely necessary to run a new lineset and what would be the difference in cost roughly ... If I'm saving 200-300 dollars but jeopardizing my warranty or systems performance ... well it's not really worth it to me. Also what is the likelyhood it would be an issue to use the current line-set after being flushed?

Finally, Do I really need an 18 SEER? Again I'm thinking efficiency, but the steep prices I'm seeing have me thinking maybe there are other possiblities out there, thoughts?
 

Dana

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The CK60-1C is a 5-ton unit. The "60" in the part number is 1000s of BTU/hr. At 12,000 BTU/hr per ton, 60,000 BTU/hr is 5 tons. The thing is 67% oversized per the Manual-J calculations and probably isn't always running sufficient duty cycles to keep the indoor humidity well controlled, though it will on warmer days.

Welcome to the club- some idiot installed a 5 ton AC system in my house in my house too, it runs for maybe an hour a day even on the warmest days, usually just one cycle. I have good afternoon shading factors and a peak cooling load a bit shy of 1.5 tons. (It might go up a half-ton when I remove a couple of 70-80' spruce trees that are too close to the house for comfort.) It cools the place off quickly when it runs, but it sucks for latent cooling. Sometimes I just leave a half-ton window shaker running upstairs, which keeps the RH under 60% for most of the house if I leave the doors open.

Given that the two separate contractors calculated cooling loads of ~30K and ~33K, you'll probably get more comfort than your current system by dropping to a 3 tonner (or even a 2.5 tonner.) Using the same sized ducts as the 5 ton system would lower the air-handler power use.

I believe the linesets can only be re-used if it's the same refrigerant. Newer equipment is almost always R410A, and in 1997 would assume it was R22, so you're really out of luck there.

At the comparatively short and low total cooling degree-day season in SE MA it's hard to make a financial case for SEER 18 even at 25cents/kwh. But from a comfort & noise point of view an inverter-drive high SEER unit with continuously variable drive or 3-4 speeds can be "worth it".

A 3-ton Carrier Greenspeed would also cover most of your heat load at high efficiency (until it drops below 25F or so), but wouldn't be a total heating solution, but the 4 tonner could be, and could save you the cost of the hydronic heating system. Play around with the settings on the "Heating Capacities" tab on this page, after inserting 35K (or whatever it was we came up with for heating) and 33K for cooling, using Plymouth weather data and +10F as a design temp. Looks like the 4-ton 25VNA048A**30 would have you covered with any of the compatible air-handlers, and with a multi-speed air handler the thing would run very long & efficient cooling cycles, probably beating the 18 SEER performance (and the ~12-ish HSPF performance as well.) You'd have to set it up somewhere that it would be protected from being buried by a roof avalanches or snow drift after a big nor'easter though.
 

rpfutrell

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I believe the linesets can only be re-used if it's the same refrigerant. Newer equipment is almost always R410A, and in 1997 would assume it was R22, so you're really out of luck there.

Contractor B suggested he could use two flush kits to clean it out enough, it sounded a bit odd. However he doubled backed said its possible, but he could also put a new line set in too if that is what I wanted.

But from a comfort & noise point of view an inverter-drive high SEER unit with continuously variable drive or 3-4 speeds can be "worth it".

A 3-ton Carrier Greenspeed would also cover most of your heat load at high efficiency (until it drops below 25F or so), but wouldn't be a total heating solution, but the 4 tonner could be, and could save you the cost of the hydronic heating system.

Interesting! So using this approach would I use the heat pump as a complimetary system? I'm under the impression for heating use it's one or the other and while it's probably possible to implement both heating systems, it probably wouldn't cost effective. On the other hand if it is reasonable possible I could get my AC all in one system. I definitely would want add the motorized dampers to the mix then to make it a 2 zone system. We had this setup at our old condo (single zone/ half the space), while we enjoyed the central air, using it as a sole heating solutions was costly on the electric bill which we learned to offset with space heaters. This makes me ask the question.... What is currently more efficient and cost effective in heating a home, electric or natural gas?
 
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Dana

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(Almost) all heat pumps are both heating & air conditioning units. Many crap out on both heating efficiency and capacity at about 25-30F, but most modulating version have legs down to at least +10F. (Some ductless mini-splits have decent efficiency down to 0F, and decent capacity down to -15F.) A GreenSpeed would have decent efficiency in your climate & 99% outside design temp, but yours is about the coldest outside design temp that I'd be totally comfortable recommending it. The fall-off in capacity below +10F steepens quickly.

The local electric and gas rates, as well as true as-used heat pump efficiency make a huge difference, there is no single answer. Most ducted heat pumps out there are rated with an HSPF of less than 10 (7 is is the legal minimum) and crap out on efficiency well before then. Ducted heat pumps where the ducts & air handler are outside of conditioned space (like in an attic, above the insulation) can be an efficiency disaster. But with the ducts fully inside the pressure and insulation boundary (say, in a semi-conditioned basement) any duct leakage or conducted heating/cooling losses from the ducts stays in the house.

Coastal MA is somewhat cooler than the HSPF test (which presumes a design temp of +17F), so a right-sized modulating heat pump will hit slightly below the rated efficiency, but up-sized a bit it'll be close. Most GreenSpeed air handler combinations test out at about HSPF 12- 13, but for the sake of argument let's assume with other losses it's effectively 10. That number means it delivers an average of 10 BTU per watt-hour, or 10,000 BTU per kilowatt hour. Normalizing every thing to kwh or $ per million BTU (MMBTU), at a HSPF of 10 it takes 100kwh/MMBTU, so at 20 cents/kwh that's $20/MMBTU, at 25 cents/kwh that's $25/MMBTU. Until last winter rates were running closter to 16 cents, which would be $16/MMBTU (if the power generators ever get over their fuel bottleneck issues, which they will- eventually.)

Wintertime natural gas has been running about $1.25-1.40 (retail, delivered all-in cost in MA). In a 95% efficiency boiler you get about 95,000BTU/therm so that's (1,000,000/95,000=) 10.5 therms/MMBTU plus the power for the boiler & pumps. At $1.25/therm that's $13/MMBTU, and at $1.40/therm that's $14.70/MMBTU plus whatever power the heating system uses.

So if your all-in electric rates are 20-25 cents like they were for most folks in National Grid's service area last winter (look at winter bills only- rates change in the summer), and your natural gas is $1.25-1.40/ therm, the marginal cost of heating with gas is still significantly cheaper. If your electric rates are 15-17 cents it's only marginally cheaper, and if the Greenspeed's system implementation is done right it could even be cheaper. But if you're heating with a crummier heat pump, a poorly laid out system with ducts outside the thermal boundary, or sized such that you have to use resistance heat back up a lot, it'll be quite a bit more expensive to run. A space heater or electric baseboard uses ~3x as much power for the heat delivered as a better-class modulating heat pump.

Key to getting the efficiency out of modulating heat pumps is to use a "set and forget" approach to the thermostats rather than overnight setbacks, since the efficiency at part load is dramatically higher than when it's running at highest speed, which it would be when recovering from setback. Folks who turn it off when they leave for work and turn it down at night will end up using quite bit more power than somebody who leaves it at 70F. (It's counterintuitive, but true.)
 
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