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Community and Q&A

HVAC “leaking”

Benjamin_Katydid | Posted in Mechanicals on

Our contractor recently installed Carrier’s newest brazillionspeed heat pump and boy do it sweat! The contractor has been really nice. They moved the pan yesterday to catch the condensation on the middlebit (the unit with the manufacturer tag on it), but the manifold just off the handler sweats, too. And it drips right into our insulation.

I don’t know whether it’s related, but the unit has been throwing “blower motor fault” off and on since they commissioned it. We got twenty such faults throughout the last couple hours of this morning. Is that related?

Our contractor has tried to assert that our attic is the problem. Whether that is true or not, he agreed to install a unit in that attic, so I need him to fix it. It’s not clear what the fix has gotta be, though. Any ideas?

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  1. etekberg | | #1

    Air conditioners in unconditioned attics are required to be insulated by code. "Catching" the condensation is not acceptable; it must be insulated with the proper insulation to prevent the condensation in the first place

  2. walta100 | | #2

    In my opinion duck work and equipment in the attic is a laze and dumb decision that saddles the homeowner with at least 25% higher operating costs. Sorry if I hurt anyone’s feeling.

    All the fixes are about how much of the needless losses can you recover.

    Option 1. Install the code required R8 insulation wrap around the ducts. Before insulating the ducts consider sealing the leaks in the ducts. Very leaky uninsulated ducts could double your operating costs.

    Option 2. Is to remove the current insulation and apply new spray foam insulation to the bottom of the roof sealing the attic from outdoors then add vents from the ducts into the attic and condition the attic air to the same temp as the house. This option makes the surface area of the conditioned space 25% larger and limits your R value because spray foam is very expensive per R per square foot compared to fluffy stuff on the attic floor.

    Option 2 is less bad than option 1 it is still what bad option do you want to pick. Option 2 more expensive than option 1 and could pay for its self if you stay in the house long enough.


  3. Expert Member
    Dana Dorsett | | #3

    The ducts & air handler need to be insulated to a code-min R8 with an air-impermeable exterior facer/skin. The laws of physics are self-enforcing- when the temperature of a surface is below the dew point of the proximate air condensation will form on that surface.

    Before insulating the ducts first need to be sealed at every seam & joint with duct mastic. (The air handler's seams can be sealed with foil HVAC tape.)

    >"I don’t know whether it’s related, but the unit has been throwing “blower motor fault” off and on since they commissioned it. We got twenty such faults throughout the last couple hours of this morning"

    Find out from the manufacturer what conditions cause the blower motor fault. The system isn't really "commissioned" until that gets resolved. It's possible that the air flow is too low (often due to ducts being too small, or a crummy restrictive filter) the supply ducts will be colder than normal, creating even more condensation. Something like that could be related to the blower motor fault condition.

    Mapping the static pressure drops across the system with a dual-port manometer is something the HVAC contractor should be able to do (if not, you can with a $100- $150 box-store manometer and some investment in your time). If it turns out the duct design is OK but the filter is too restrictive with a big pressure drop, cutting in an oversized 4-6" deep pleated filter would allow more flow. This sort of problem is all stuff that the contractor should have figured out up front.

    Often high SEER equipment needs fatter ducts (or a lower cfm air handler) to work on existing duct systems, but may be able to work with a smaller, more right-sized heat pump. The vast majority of AC and heat pump systems in the US are woefully oversized, often more than 2x ore more oversized for the design cooling or heating loads. A heat pump that's 1.2x oversized for the 1% design condition cooling load and 0.9-1.2x oversized for the heating load might have a sufficiently low cfm to use smaller pre-existing ducts from an older 1 or 2 speed old school SEER 10 type system.

  4. Benjamin_Katydid | | #4

    Thanks everyone. A couple contractors performed man J calcs and came up with 2.5 or 3 ton. We installed 2 ton because a) one contractor said that's what would suit our existing ducts and b) we have done a lot to seal the envelope and that wasn't being taken into account in their models.

    This contractor replaced all the accessible ducts with new r8 ducts. I know there are leaks somewhere because the attic is cooler in the morning than it ought to be. If they were supposed to insulate the handler by code, that should be a warranty issue. We will see what a blower motor fault means before we touch base with them.

  5. ChadStover | | #5

    Benjamin, I have a Carrier heat pump and air handler installed last year with a similar issue. It's not the Greenspeed but the model below that with 5 different speeds. When the weather is hot and humid (I'm in Delaware, on the coast), I often get errors 44 and 40 related to the blower motor. The unit shuts down. Sometimes it corrects itself and restarts.
    Sometimes that takes a day or so. The installer replaced everything but the air handler box last August. We had no issues until late June of this year. Now the same error codes are appearing again.
    My air handler is installed in a sealed attic. The attic is sealed with open cell spray foam. I don't have a supply or return in the sealed attic. The humidity in the attic runs higher than in the house, which is a known issue with open cell foamed sealed attics. My ducts are insulated to r-8. But the air handler itself is not insulated. I get quite a bit of condensation on the air handler when the humidity is high. My hypothesis is that the condensation is getting into the electronics and causing the fault codes. To test this, I am going to reduce the humidity in the attic with a dehumidifier and see if the fault codes stop.
    I should note that I have the same air handler installed in a downstairs utility closet and I have had no problems with that unit. I've also never seen condensation on that unit.

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