Installing Central AC options in 1980s House

Discussion in 'HVAC Heating & Cooling' started by Brendon, Jan 28, 2020.

  1. Brendon

    Brendon New Member

    Joined:
    Jan 31, 2019
    Location:
    Hingham, MA
    Greetings professionals!
    I'm on South Shore in Massachusetts and have just purchased a 1980s colonial with no central air.

    To paint a picture, it is 3400 sf, attached 2-car garage with a "great room" above the garage. The first floor has 4 rooms: a kitchen, dining room, living room, and 4-season room. To access the great room, one must walk up about 5 steps (and walk down 5 steps to access the garage).

    The second floor has 3 bedrooms: a master bedroom which is 12x27, along with two kids bedrooms (plus 2 full bath).

    The challenge....there is a walk-up to a third floor, which has two more bedrooms (plus a full bath). There are knee walls on the outsides of the 3rd floor bedrooms, but there is limited rough attic space. There is a small ovehead attic, but very limited elevation (most likely one would have to crawl).

    The previous owner used about 7-8 window unit air conditioners. After retrofitting ac in my current 2k sf split level ranch (which was relatively easy given the unused attic space to drop-down the air handler and vents), this new home represents a challenge for the following reasons:

    1. The great room has no basement or attic below or above, as below is the garage and it's vaulted...one option I've considered is installing ductwork in the garage (later to be soffited).

    2. The first floor should be achievable as the basement has high ceilings and can bring in ducts into the floor of the first floor.

    3. The second floor will be a challenge, because there are 3rd floor bedrooms, so I'm not sure how to best handle this....perhaps we can utilize the limited attic above and/or knee walls?

    I can't wait to hear your recommendations! We move in this week and getting the hvac squared away before summer is priority 1. We're open to options, but I'm considering traditional hvac, or unico high velocitiy, ductless, or a combination of the 3, perhaps ductless in the great room and ducts throughout first floor.

    Also, please provide suggestions on installers who can handle this, I'm leery of the complexity of this job, probably not best for beginners!

    Thanks!

    Brendon
     
  2. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Before wasting a ton of money on an oversized zoned central system that provides neither comfort nor efficiency, run a room by room, zone by zone Manual-J heating and cooling load calculation (or pay an engineer, not an HVAC contractor to run those numbers for you.) The odds are pretty good that the whole-house cooling load is less than 3 tons, and the odds are also pretty good that a random HVAC contractor is going to propose something in the 5 ton range or higher. If you want to take a stab at it yourself, freebie/cheapie online tools such as coolcalc.com or loadcalc.net aren't bad if using sufficiently aggressive (not conservative) input assumptions, but be forewarned that most newbies (an even most HVAC contractors) have a huge tendency to err toward the conservative side, leading to grossly oversized equipment.

    Coolcalc is a fully registered true Manual-J tool. Loadcalc is only "Manual-J-ish", but not terrible for ballparking it. For either, assume the house has VERY tight constructions and the system has VERY tight ducts, fully inside both the insulation and pressure boundary of the house. (If you have a stupid-attack and opt to put the ducts in the attic above the insulation, or behind insulated vented kneewall attics you invite a whole host of misery during the heating season, and lower efficiency during the cooling season. DON'T let that happen to you!)

    Zoning by floor is usually the best option, and if you have the space, three separate right-sized systems (right sized for their zone loads) is going to be both more comfortable and more efficient- and often cheaper to install.

    A sketch of the floor plan, marked with both heating and cooling loads for each room would be useful here.

    Is the basement built out as finished living space? Are the foundation walls and band joist insulated?

    How is the place currently heated? (If oil or propane there may be substantial MassSave rebates for going with heat pumps vs. cooling-only solutions.)

    Tall Great Room spaces can often be cooled/heated better with a single ductless wall coil or floor console than with ducts, unless it's truly huge. But to get the placement & sizing right takes a bit of analysis. It's rare to have a Great Room that works well when zoned with a bunch of normal size/height rooms, and they usually have a sufficient load to warrant a dedicated mini-split. Also, running the ducts through a garage requires that the enclosing soffit be fully air tight, and meet code requirements as a fire barrier wall.
     
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  4. Brendon

    Brendon New Member

    Joined:
    Jan 31, 2019
    Location:
    Hingham, MA
    Thanks for the thoughts Dana!

    It is oil-heat basedboard radiators, and has a brand new Buderus heating system. Unfortunately, I can't provide a sketch of the floor plan or run the cooling load calculation at this time (i've tried, but it's a bit more technical than what I'm looking to do).

    The basement is currently unfinished, and no insulation on the basement foundation walls and/or rim joists.

    I agree that zoning by floor (3 zones: first floor, bedrooms, and great room).

    I'd be more then happy to hire a professional run a load calc and work it that way...suggestions on those on the South Shore?

    Incidentally, in calling several local hvac installers, none of suggested doing the load calc (obviously doing exactly what you suggest and provide and overkill type solution). The problem is that many hvac installers only go with what they "know" and their knowledge is limited to doing it the only way they know how to do it!

    I do like the idea of the ductless unit for the great room, as there is a wall that is not all that visible (and good for an air handler unit), but ideally I'd prefer not to have ductless throughout the house due to the size (an unsightliness) of the indoor wall-mounted air handler.

    Ultimately, I'm willing to hire someone who can run the calcs and make the recommendations and do the installations.
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Ductless throughout the house usually ends up with truly grotesque oversize factors and inefficiency, even if you thought high-wall coils were beautiful! :)

    The "ductless head in every room" approach is only a good idea for an HVAC contractor behind in their boat payments, not in your house, or anybody else's house.

    MassSave will subsidize squirting a couple inches of closed cell foam on the foundation sill and band joist, but not the foundation. Even in an unfinished basement it's "worth it" to insulate the foundation, especially if it stays warm down there on the standby & distribution losses of the oil-boiler. The warmer the basement, the higher the losses. An 8" thick poured concrete wall has an R-value of about R1.35. So even when its only 35F outdoors and 60F in the basement (a 25F difference), every square foot of uninsulated above grade foundation wall is losing 25F/R1.35= 18 BTU/hr per square foot. In a typical house that adds up to several tens to more than 100 gallons of oil per year in a location like Hingham.

    I'm not sure who to recommend for load calculations or system design in your area. A quick web search RESNET raters and Hingham came up with these people, who may or may not be competent to do the load calculations, but it's worth checking out (and getting references.) Don't let a RESNET rater run the system design numbers though- that's s different skill.

    These consultants in GA are pretty sharp and do fairly competent load designs as well as system designs, and will work remotely online, but they're not cheap. (I've reviewed a couple of their Manual-Js and equipment recommendations for projects the did remotely in MA over the past handful of years. One of their principals is a guy named Allison Bailes III, who writes blog bits for GBA, and often presents at NESEA and other regional home-efficiency conferences.)

    At current oil & electricity pricing the operating cost of heating with a better class right sized (within reason) heat pump is cheaper than heating with oil. But even if the heat pumps ended up under sized for fully covering the 99% design load odds are pretty good it would still be cheaper than heating with oil in a winter as mild as this one has been so far. And that's even assuming the oil boiler isn't grossly oversized for the heat load (which is probably assuming too much.)

    Oil is running about $3/gallon in MA right now. With a source fuel energy content of 138,000 BTU/gallon burned at 85% efficiency, with no idling losses about 117,300 BTU/gallon ends up going into the heating system. Normalizing to $/MMBTU (million BTU) it works out to 8.5 gallons/MMBTU x $3/gallon = $25-26/MMBTU.

    Hingham has it's own municipal power company, which probably has residential rates well below the statewide average of ~22 cents/kwh. A heat pump rated with a so-so HSPF of 8.5 (= 8500 BTU/kwh) it takes 118 kwh/MMBTU, which is also about $25-26/MMBTU. But a cold climate heat pump rated at HSPF 11 (some are as high as 14) is subtantially cheaper, even at EverSource or National Grid type rates. If HMLP's rates are under 15 cents/kwh (and it looks like they are) is substantially cheaper even with a so-so HSPF 8.5 heat pump. It wouldn't surprise me if heating with even half-way decent heat pumps came in a half the operating cost of a pretty-good Buderus oil burner.

    Being on a municipal power grid may mean you don't qualify for MassSave incentives, but it looks like Nat'l Grid serves gas in your area, so in fact you might, even if not hooked up to the gas grid. This is something to check out as part of the whole HVAC and insulation upgrade analysis, since it's potentially several thousands of dollars that might be left on the table.
     
    Last edited: Jan 28, 2020
  6. Brendon

    Brendon New Member

    Joined:
    Jan 31, 2019
    Location:
    Hingham, MA
    Wow that was a pretty intense knowledge bomb dropped on me, thanks!
    Sounds like I've some work to do in terms of insulation in the basement.
     
  7. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    If the basement is being converted into living space it's sometimes easier/cheaper to put R5 or higher rigid foam board up against the foundation and install a 2x4 studwall with R13-R15 batts to hit code-level performance. It's generally safer/better to go with UNFACED batts, and install 1" of EPS foam under the bottom plate of the studwall as a thermal & capillary break. An inch of foil-faced polyiso is cheaper/greener/better than R5 XPS (the absolute worst insulation in common use today from an environmental point of view), which is sufficient exterior R for dew point control at the foam/fiber boundary on the above grade portion without requiring an interior side vapor barrier (which shouldn't be used in basements because it creates a ground moisture trap.)

    Polyiso is somewhat hygroscopic, so the cut bottom edge needs to NOT rest on the slab or extend below the high tide mark if the basement has a history of flooding. Filling in the moisture prone bottom with EPS board would be fine.

    If it's not being finished, using 3" of reclaimed roofing polyiso strapped to the wall with 1x4 furring through screwed to the foundation can be dirt cheap. There are several vendors handling reclaimed roofing foam in MA, including a couple larger vendors. From a design point of view, no matter what the labeling says, derate any used roofing polyiso to R5/inch, and any used XPS to R4.5/inch for design purposes. EPS doesn't lose performance with age, and Type-VIII (1.25lbs per cubic foot density) roofing EPS runs about R4.1/inch, Type-II (1.5 lbs density) R4.2/inch. IRC code minimum is R15 continuous insulation. Any used foam (even XPS) is greener than any virgin stock foam, since no new polymer or blowing agents are required- reuse just piles on to the benefit side of the cost/benefit balance on an environmental hit already taken.

    To meet fire code foam board has to be covered with a timed thermal barrier against ignition. Installing half-inch wallboard on the 1x4 furring meets that requirement, painted or not.

    The used-foam & furring solution is almost always ends up cheaper than new 1" polyiso + R13 batts, but is more of a PITA for running electrical wiring if you decide to turn it into living space. (I did my basement with 3" polyiso someone scavenged from a building demolition in Fitchburg, selling for $20 for a 4 x 8 sheet, but I've seen it as cheap as $12 and as expensive as $25 on other projects since, as market conditions changed.)

    If you can, install the wall foam before taking MassSave up the band joist & foundation sill spray foam subsidy to provide a more perfect air seal where the wall foam meets the foundation sill foam. If that subsidy isn't available to you, cut'n'cobbled foam board sealed to the joists/sills/subfloors/ foundation-top with can foam works (and is greener than sprayed polyurethane foam.)

    Basement insulation details have been covered on several threads here over the past handful of years, but if you want more project-specific input when the time comes go ahead and ask.
     
  8. fitter30

    fitter30 Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    With multi level house more than one system is needed for comfort and efficiency. http://spacepak.com is a hi velocity duct system that you might want to look at. There are other companies that have similar systems. Bosch and others our making variable flow heat pumps central systems that are very efficient.
     
  9. Brendon

    Brendon New Member

    Joined:
    Jan 31, 2019
    Location:
    Hingham, MA
    Yes, I just had a company come out and they're proposing 8 ductless evaporator units, basically one for each bedroom and one for each living room area. They do almost exclusively ductless....I'm not sure that is the right solution for our needs.
     
  10. fitter30

    fitter30 Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Minis are quiet, energy efficient, zoning and no duct loss. Now the bad - multi evaporators systems- heat pumps when in defrost no heat there is no strip heat in them, filters are very thin, when they need cleaning- water, cleaning solution, tarps, ladder and blower wheel is removed (look at a you tube). Parts might take a day or two, have a refrigerant leak could be in any evap or piping per condenser. My house 1900 sq ft 2 story have two systems three evap per. Installed this because wanted to get away from duct in crawl space and zoned. Two systems in case one went down im very rural. Be sure to check with your electric company for any rebates.
     
  11. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609

    I'm pretty sure it's the WRONG solution for your needs, better suited to the financial needs of the installer than what would deliver optimal comfort & efficiency to you.

    This issue was covered (again) in today's GBA blog. (It's behind a paywall, but you can take a free trial subscription. There are links to multiple other blogs on closely related topics.) The outdoor unit has to be sized to the whole-house load, even if it can't support that many zones.

    Mini-duct cassettes right sized for the loads of the multiple rooms it supports is a far better solution. But "...exclusively ductless..." contractors are often completely clueless how to handle low-static (or even mid-static) ducted mini-split cassettes.

    There really is no substitute for running the room by room load numbers, and that's even more critical with a multi-zone ductless system.
     
    Last edited: Feb 7, 2020
  12. Brendon

    Brendon New Member

    Joined:
    Jan 31, 2019
    Location:
    Hingham, MA
    I agree Dana, mini splits with wall mounted evaporators is the wrong approach for each room of the house. I've always been of the mindset that it'll take some significant planning, and ultimately, a "hybrid" approach that makes sense, comfort-wise, along with financial and visually.

    After having several contractors submit a quote, including one by a local "high end" hvac technician, who emailed me a quote (without ever stepping foot into my house!), we think we've found a solution!

    It'll likely be a three zone system, Zone 1, which is the great room over the garage, will be a mini split system. Like use a concealed heat-pump in a fake wall with dead space behind it.

    The technician is returning with the supplier to do a measurement and calculation for all zones.

    Zone 2, will be a traditional ac system, with an air-handler in the basement, and ducts going to each of the 4 rooms on the first floor. The ducts will come up through the basement, and be mounted on the floor or on the bottom part of the wall.

    Zone 3, which will cover the 2nd and 3rd floor, will likely be a high-velocity system. There are 3 bedrooms on the second floor, and 2 bedrooms and a full bath bump-out on the 3rd floor directly over the 2nd floor bedrooms. This is the challenge as there is only small knee walls on the outside edges of the 3rd floor bedrooms, and the technician took his time and figured that there was full runway in the joists directly below the 3rd floor bedrooms.....thus he can run his unico ductwork from the front of the house to the back, and hit all of the bedrooms and baths in the 2nd and 3rd floor.

    I think we're on the right track! What do you all think? I'm especially appreciative of the amount of time he took to really assess the logistics of the project, it is very complex when you have the layout we do! The fact that he'll return, with the supplier, to do all of the sizing calculations, is especially comforting. I'll be sure to share more details once that has happened.
     
  13. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    It's generally better to have a disinterested third party do the load calculations But as long as you've impress upon the contractor doing the load calculations that you absolutely DON'T want the system to be oversized, and that they should use aggressive assumptions about R-values/U-factors/infiltration rates they probably won't come up with anything too outrageous. The industry track record is pretty lousy though.

    I'm inherently predisposed to discount the accuracy of any contractor/distributor/supplier load calculations- perhaps I'm just getting jaded, but I've long since given up using anything but competent third party load calculations, and let the contractors work from those numbers rather than their own. A couple of years ago I reviewed a contractor Manual-J on a superinsulated house in central MA that had R50 walls and an R100 roof, with U0.15 windows where the contractor had filled in all code-minimum numbers into tool. It was ridiculous. The engineer who RE-did the Manual-J supplied an appendix showing the parallel path calculations use for coming up reasonable U-factors of all of the non-standard construction elements.

    Did the tech look up the SHGC specs your windows, or at least check which surface the low-E coating is on? There's a pretty big difference in solar gain between clear glass double-panes and a low-E on surface #2 or #3, and significant enough differences in the types of low-E coatings, and whether it's on surface #2 or #3. If they're just guessing the human instinct is to be conservative rather than aggressive, but you'll be more likely to get it right being aggressive on the guesses.

    As an alternative to Unico, Dettson's skinny Smart Duct systems fit easily in 2x4 framing bays. Their tiny Chinook gas furnaces & air handlers work with their modulating Alize 3/4 ton ducted minisplit (which is also a heat pump, not just AC), and are easier to right-size for lower-load zones covering several rooms. But without an independent load calculation it's hard to choose that over something calculated by the contractor and their suppliers. High velocity is only need if high cfm is needed, and most room-sized loads don't really call for high velocity.
     
    Last edited: Feb 14, 2020 at 11:53 AM
  14. WorthFlorida

    WorthFlorida Retired

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    In defense for HVAC guys. The problem is the customers expect more from a AC system than what is usually installed. The biggest headache is multi floor homes. As you know heat rises and when you do get those hot summer days, the upper floors are generally not cool enough since the heat load is more than than what the AC can handle, even with all calculations. Scenario is that 90 plus week of heat the customer calls that my ac doesn't seem to be working right. The tech comes out and of course cannot find anything wrong. Then the customer is pissed that the HVAC company installed the wrong size system. "you sold me the wrong system, etc, etc." and won't pay the bill. Then they rag on the company on social sites or google reviews. No one complains if it the house is too cold since all they need to do is raise the thermostat. Most customers don't care about short cycling or know what it is and they rather be cool and damp than warm and dry. It is a hard balancing act, happy customers and a good engineered AC system.
     
  15. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609

    It's true that there is a customer education/expectation problem too, which is partly why I take the time in forums to explain to people why they're uncomfortable and how to fix it. Nate Adams has created a whole business around it. The HVAC people are the first to get blamed, and it's definitely not fair- the HVAC contractor isn't tasked with properly air sealing or insulating the building, or specifying the windows. But I wish more would figure out how to better measure those things and deliver more optimally sized equipment, even for the thermally deficient homes.

    Heat doesn't rise. Hot air rises, but only if it's allowed to. The temperature deltas between floors are NOT usually primarily due to stratification , but rather infiltration from abyssmal air sealing at the attic floor plane & foundation, and insufficient or poorly implemented insulation. Houses that actually meet IRC spec for air tightness & duct tightness & R-values have much better control over stack effect & convection driving floor to floor loads, making it much easier to spec the equipment.


    That is for sure a movie playing near you, no matter where you live. It happens. That's how Nate Adams makes a business out of a whole-house approach, never just HVAC, never just air sealing & insulation. His retrofits in old houses are more comfortable and use less cooling & heating energy than most new houses (often despite lower R-values) by controlling all aspects of the loads, and sizing the equipment accordingly.

    In Hingham MA they complain if the house is too cold- it's a heating dominated climate. :) That's why the typical hot air furnace in MA is 3-4x oversized for the 99% load, with AC sized to suit (since the air handlers are so huge). And that's why the bonus room over the garage sees huge temperature swings in winter & summer, and why it's clammy indoors in summer rather than comfortably cool & dry. Modulating equipment helps, but isn't sufficient at 3-4x oversizing. Keep it under 1.5x and there's a shot a delivering real comfort.
     
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