Odd situation about HVAC permit

Discussion in 'HVAC Heating & Cooling' started by chuyue, May 28, 2021.

  1. chuyue

    chuyue New Member

    Joined:
    Nov 5, 2020
    Location:
    Maryland
    I'm finishing my basement. I started work last year and added a few vents to condition different zones of my basement last summer. I simply tapped them into the main trunk. My whole project was delayed and I'm now getting ready to put up drywalls. BUT I was told by my plumbing inspector yesterday that I need to have a licensed HVAC contractor to pull permit and get it inspected, and this is a new requirement by county effective Jan this year. He was telling me that I need the calculation and proper duct sizing etc.
    I don't know what that would entail as I have installed the ductwork and made soffit around them. I will have a contractor coming in next week to take a look and let me know what's cost to get it pass inspection. I'm really worried if they ask me to rip off the soffit to update the duct sizing. It really sucks.
    Has anyone ever dealt with this situation before? what does inspector really look for during the inspection?
    Thanks!
     
  2. breplum

    breplum Member

    Joined:
    Oct 2, 2004
    Occupation:
    Plumbing and heating contractor
    Location:
    San Francisco Bay Area
    The inspector is asking for duct design and the way we do that these days is with a computer program.
    (When I was first training, we used pencil, paper and calculator).
    The house should get a load calculation done with software and then duct design is pulled from that.
    Your energy consultant or contractor, if he has the software will be able to provide the calcs and duct design.
    You cannot get home comfort properly balanced by just tapping in branch ducts willy nilly, because it is based on scientific engineering these days.
     
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  4. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    In our dreams they would be actually designing ducts using an engineering process! (I really do wish that were true...) But that's rarely the case when tapping in to pre- existing duct systems. If a complete duct design/analysis is now a requirement for remodeling in Maryland it's going to generate a lot of busywork for little gain.

    In general basements need to be run as a separate zone, since the heat loss characteristics are very different from fully above-grade spaces. Simply adjusting the registers isn't usually enough to provide true comfort unless it's a very well insulated house (including the foundation walls) and the equipment is correctly sized for the load. Most gas furnaces in the US (including MD) are already 3x+ oversized for the load, and if that's the case here while there is ample capacity for including the basement load, the duty cycle will still be too low to get a reasonably consistent temperature balance floor to floor.

    There are very few HVAC contractors competently performing load calculations, (preplum notwithstanding) the industry as a whole has a tendency to be far too conservative on inputs and end up with 99% design load numbers 2x over reality. (Garbage in == garbage out.) They then apply ASHRAE's recommended 1.4x oversizing factor, pick equipment that covers that with a bit of margin and still end up with a 3x oversizing factor, delivering an uncomfortable hot/cold low duty cycle even at design condition. (Right sized equipment would be running a 71% duty cycle at design condition- blowing warm air 40-45 minutes out of every hour on the coldest nights of the year, and nearly 100% during Polar Vortex disturbance cold snaps.)

    A disinterested third party such as a professional engineer should be the person running the numbers, someone who makes their living and reputation on the accuracy of their numbers, and NOT someone whose bread is made selling/installing/servicing HVAC equipment. RESNET/HERS raters could run the load numbers, but wouldn't be able to analyze or specify the ducts. Duct design is within the wheelhouse of many engineers who run heating & cooling load numbers, but that part may end up having to be left to an HVAC contractor. (Good luck with that!)

    (As preplum knows better than I) under Title 24 laws California has required load calculations for additions & renovations for over a decade now. But even there many HVAC contractors have settled for figuring out how to tweak the inputs in the tools to make them deliver what matches the crap they just installed, and it takes a pretty savvy inspector (or an outrageously egregious set of tweaks) to call them on that kind of BS. I'm somewhat hopeful that it's getting better over time in California, but since this is a new requirement for Maryland my expectations of the average local HVAC contractor getting it right are low.

    So how you go about it depends on what your goals are- do you want to get it right, and end up with the most comfortable version of the house possible? Or do you just want to satisfy a line item for the inspector and move on with your life?
     
  5. chuyue

    chuyue New Member

    Joined:
    Nov 5, 2020
    Location:
    Maryland
    Thanks for the replies.
    I'd choose cross a line item and move on. It's not like I don't want to get it right, I just don't believe there is a right point to begin with anyway. I know all these codes and California stuff have good intention but they live in their fantasy land sometimes. I can do the duct design and calculation all day long but that is on paper. When it comes to installation on site, things got adjusted all the time. Even a homeowner close a few vents could affect the balance anyway.

     
  6. chuyue

    chuyue New Member

    Joined:
    Nov 5, 2020
    Location:
    Maryland
    Ok, here is some update and my plan:
    Our county posted this in its website now after I pointed out that they did not have it on the website:
    "Beginning January 25, 2021 mechanical extensions to additions, finished basements or alterations to an existing system will require a mechanical permit and inspections.
    All newly installed heating or cooling ducts and exhaust duct will be installed per the 2018 International Residential Code and the 2018 International Energy Code.
    Drawings must accompany the permit application as well as a signed affidavit from master license holder that the existing system has been calculated for the additional load and it will adequately supply heating and cooling. A manual J will not be required for an alteration or addition permit. "

    I called four AC firms to ask if they could help me to pull permit. Three said "no", the other said the conservative estimate is $2000. I have another guy coming in this Friday to take a look and get me a quote. They told me that the new requirement is nonsense because the county ask contractor to put their name on the line then in the end the manual J is not required. No responsible contractor would risk that so the manual J must be done. The one quoted me 2 grand will do manual J (could cost cost more depending on the result!). One of them told me some homeowner asked them for the same reason a few days ago so I'm not the only victim...
    I won't be able to cough up two grand for this unplanned event so I want to throw out a potential resolution for your input:
    I will tell my inspector that I will seal the vents that I installed and put up drywall without cutting the vent so there is no "mechanical extensions to finished basements or alterations to an existing system". I will not install doors to the rooms that I originally framed out so all the space will be connected except bathroom having a door. I can cut out the vents and install doors after the county signs off the final inspection.
    Of course I might need to revise my building permit to remove these doors, but it is only $50 filing fee.
    Do you think this is a viable solution? Thanks.
     
  7. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    If you need heat install a few electric baseboard heaters. (electrical permit need). If you need some AC, small window units if possible will work for the few months needed. Electric baseboard is not that expensive in electric cost. You can turn up the thermostats when needed.
     
  8. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    I know it's still pandemic pricing, but 2 grand for a Manual-J is ridiculous, especially if it's an HVAC company doing it, unless you have the oddest collection of non-standard construction where U-factors have to be separately calculated and entered. If it's an 'merican style post-1945 stick built house with a poured concrete or CMU foundation with normal windows (any vintage) and doesn't have a completely weird shape like 17 corners to the footprint and a dozen odd dormer it should be under a grand (normal times), but probably still more than $500.



    Reversing your duct modifications gets rid of the extension issue. Do finished basements required by code to be heated & cooled? What does removing the doors buy you, exactly?

    Whether somebody else does it or you do it, it's still worth running a room by room Manual-J on the place to know where you are with it, and to be able to plan for comfort. It doesn't take a lot of time. While online Manual-J-ish tools like LoadCalc & CoolCalc are like somewhat stripped down versions of a pro tool, in the hands of newbies it's easy to screw it up. The BetterBuiltNW HVAC tool is simpler and easier to use (but with Manual-J underpinnings) and still seems to give reasonably accurate load numbers. (I've only used it on a single project so far- I haven't pushed it's limitations very hard.) A primary difference between BetterBuiltNW and the others is that it uses reasonably aggressive defaults on U-factors & air leakage. It also has a duct design portion (that you should probably ignore unless you know what you're doing.)

    The target audience for that tool was for HVAC pros installing heat pumps. The chronic oversizing thumb on the scale that most HVAC installers have doesn't lead to efficiency problems when the equipment is hot air furnaces (although there are often comfort consequences from 2x+ oversizing), but oversizing heat pumps has compounding issues of significantly higher upfront cost, significantly lower as-used efficiency, as well as lower comfort.

    If you run room by room load calculations on both the basement and the rest of the house you'll probably find that your AC is more than 1.5x oversized, and the furnace more than 3x oversized. (If I'm wrong, be happy!) ASHRAE recommends no more than 1.4x oversizing for hot air furnaces (rarely found in real houses unless the equipment was specified by an engineer, not an HVAC contractor). With cooling 1.2x is a better oversize factor to use for single or 2 stage system, but with modulating systems with a 3:1 turn down or greater it's still fine at 1.5x. Above that efficiency & comfort tends to fall off. AFUE testing on hot air furnaces uses a presumptive 1.7x oversize factor, an oversize factor that's still fine for efficiency, but is a bit lacking from a comfort point of view (unless it's a 2 stager).

    Sizing your basement heating air flows to be the same oversize factor as the furnace & flows are to the rest of the house would make it track sort-of reasonably operated as a single zone in the middle of winter, but the basement cfms may need to be tweaked upward during the shoulder seasons, since basements don't get much solar gain benefit, and has the constant heat draw of the cold basement slab (unless you insulated the slab.)
     
  9. chuyue

    chuyue New Member

    Joined:
    Nov 5, 2020
    Location:
    Maryland
    My house was a standard colonial style built in 2016, and was very energy efficient back then. It is in a community with cookie cutter style. My neighbors on the left and right finished their basements two years ago. We have almost same floor area/plan, exact AC&furnace. They had no issues with adding extra vents. I added my vents last fall so it's been operating like this for 10 months with no comfort issue. As much as I want to do it "right" but not a 2 grand "right"!

    My builder actually had installed a return and two supply vents in the basement originally so the basement has been technically conditioned. Removing all the doors will connect all basement as one open space which is to be conditioned by the original system design to be in compliance with the IRC (I'm not sure if this is true or not but want to check with folks here who know about this).
     
  10. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Usually in developments with "cookie cutter style" the exact same HVAC equipment is installed in every home, but sized for the very largest/highest-load homes in the development.

    If it was built in 2016 to IRC 2012 or IRC 2015 code levels the basement walls would have been insulated with R10 continuous insulation (preferable), or a 2x4/R13 studwall inside the foundation walls. Most tract home builders would have used the R13 studwall approach- is that how yours was built?

    Only better than code homes or homes heated with radiant floors would have insulation under the basement slab.

    The IRC says nothing about open spaces. The IRC 2012 specifications for HVAC return air lives here.

    If there have been no season comfort issues with the hacked in system operating it as a single zone the basement is clearly sufficiently insulated and sealed to make it work.

    Open doorway returns are extreme overkill. Supply-ducts-only to doored off rooms are a problem, since it pressurizes the room relative to the outdoors, and depressurizes the rooms with the returns, forcing outdoor air infiltration. But this effect can be mitigated to near-zero without resorting to full-on return ducting to the return plenum or removing the doors.

    To hit Energy Star performance with the doors closed (=< 3 pascals pressure difference from room to room) every doored off room needs a dedicated return path of adequate size to the common return space. Unless your supply cfm for the room is truly titanic it doesn't require anything nearly as large as an open door. For the low low cfm requirements needed to heat & cool an insulated basement room a transom grille or jump-duct built into a partition wall would be enough.

    [​IMG] [​IMG]
    ...or...

    [​IMG]

    To meet current code when using stud bays as return paths it needs to have hard piped duct in the wall. There are 3.25" x 14" ducts (even at box stores) purpose-made for installing in 2x4 partition wall stud bays, as well as 3" x 10" - 3" x 14" ovals (which tend to be a bit quieter than rectangular duct). As with any duct system, seal all seams and joints on jump duct returns with duct mastic to reduce leakage & noise. For high cfm rooms it sometimes takes 2 (or even 3) stud bays to get there, but I'm guessing your supplies to those rooms are 6" rounds(?) or smaller, and a single ~3" x 14" jump duct would be plenty. Whatever the cross sectional area of the supply duct to the room is, as a total-hackery rule of thumb sizing the jump duct at 1.5x that cross sectional area or larger would still make it. (That's a LOT smaller than an open door, eh?)

    If the ceiling joist bays are deep enough an 8-10" round can work with transfer grilles on the ceiling.

    [​IMG]

    For jump ducts in joist bays it is better to use right angle duct boots or hard-piped ells right out of the duct boots and keep the flex (or hard piped) horizontal section straight to avoid kinks or flattening of the flex duct.
     
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