Adding Ducts From Existing HVAC To New Finished Basement

[jaybrown]

How do you guys approach adding ducts from existing HVAC units to a new finished basement?

I've talked to multiple inspectors who have varying opinions from requiring Manual J's to be submitted with a letter stating their units can handle the increased living space and I've also come across inspectors who say that responsibility should fall on the homeowner and contractor to ensure proper sizing and he just verifies the duct work meets code(given the basement isn't massive).

I have a lot of new construction in my area and the pattern is homeowners close on the house and after the one year warranty inspection the finished basement and deck permits come flooding in.

 

[Yankee Chronicler]

I don't see how you can issue a permit to add conditioned living space without calculations documenting that the system has capacity to heat the additiojal volume. Air conditioning isn't required by code, but heat is.

For a code official to say, "I'm just permitting a duct" is a very limited, short-sighted approach. From the 2021 IRC:

M1401.3 Equipment and appliance sizing. Heating and
cooling equipment and appliances shall be sized in accordance
with ACCA Manual S or other approved sizing
methodologies based on building loads calculated in accordance
with ACCA Manual J or other approved heating and
cooling calculation methodologies.

Exception: Heating and cooling equipment and appliance
sizing shall not be limited to the capacities
determined in accordance with ACCA Manual S where
either of the following conditions applies:

If they're adding livable floor space, they're increasing the building load for both heating and cooling. The code official can't ignore that.

 

[bill1952]

Was the basement "new" or was it just "finished"? Was it heated and this just different distribution? I've never lived in a house with a basement that wasn't heated, finished or not.

 

[jaybrown]

Was the basement "new" or was it just "finished"? Was it heated and this just different distribution? I've never lived in a house with a basement that wasn't heated, finished or not.

New construction that was unfinished and not heated when settled, now it is being finished the homeowner just wants to branch off the existing trunks to heat the proposed finished basement.

 

[steveray]

New construction that was unfinished and not heated when settled, now it is being finished the homeowner just wants to branch off the existing trunks to heat the proposed finished basement.

Sounds like they are increasing the conditioned space by 50% so either the initial install is wrong (as you can't oversize by 50%), or the change doesn't work...

 

[mtlogcabin]

2018 IBC
[F] 903.2.11.1.2 Openings on one side only.

I have a lot of new construction in my area and the pattern is homeowners close on the house and after the one year warranty inspection the finished basement..... permits come flooding in.

New construction should require the HVAC system to include the basement whether it is finished or not. It is cheaper to insulate walls than it is the floor system
Energy Code
BUILDING THERMAL ENVELOPE. The basement walls, exterior walls, floors, ceilings, roofs and any other building element assemblies that enclose conditioned space or provide a boundary between conditioned space and exempt or unconditioned space.

 

[klarenbeek]

Around here an unfinished basement with NO heat would have had possible water pipe freezing issues last week. -30 degrees + northwest wind can cause all sorts problems. Not sure if Pennsylvania gets quite that cold but its gotta be close. Plus as stated above the unfinished basement is still in the thermal envelope and should be included in the original equipment sizing. A basement is typically a much smaller load that the main level.

 

[bill1952]

Is there a thermal barrier between basement and main floor?

 

[jaybrown]

Is there a thermal barrier between basement and main floor?

Most new construction around here opts for the blanket insulation on the basement walls instead of the insulation in the floor joist bays.

 

[jaybrown]

New construction should require the HVAC system to include the basement whether it is finished or not. It is cheaper to insulate walls than it is the floor system
Energy Code
BUILDING THERMAL ENVELOPE. The basement walls, exterior walls, floors, ceilings, roofs and any other building element assemblies that enclose conditioned space or provide a boundary between conditioned space and exempt or unconditioned space.

I wasn't involved in the initial plan reviews for new construction but the builder confirms the units are not sized the same if it finished or unfinished.

An unfinished basement is in the building thermal envelope but is it a habitable space(R303.10) which would require heating? Cheap builders aren't going to offer larger systems if they don't have to.

 

[mtlogcabin]

i would like to know what section says that.

An unfinished basement is in the building thermal envelope but is it a habitable space(R303.10) which would require heating?

A basement does not need to be finished to meet the definition of "Habitable". How is the basement used by the occupants? Is it a play room for the kids? Is it dad's man cave to watch sports on tv. Is a future bathroom under slab DWV system installed. Are egress windows provided? That is what would you should be looking at and then you require the HVAC system to be sized to provide heat in the basement.

[RB] HABITABLE SPACE. A space in a building for living, sleeping, eating or cooking. Bathrooms, toilet rooms, closets, halls, storage or utility spaces and similar areas are not considered habitable spaces.

R303.10 Required heating.
Where the winter design temperature in Table R301.2(1) is below 60°F (16°C), every dwelling unit shall be provided with heating facilities capable of maintaining a room temperature of not less than 68°F (20°C) at a point 3 feet (914 mm) above the floor and 2 feet (610 mm) from exterior walls in habitable rooms at the design temperature. The installation of one or more portable space heaters shall not be used to achieve compliance with this section.

 

[steveray]

It's finished when I am done....

 

[bill1952]

Most new construction around here opts for the blanket insulation on the basement walls instead of the insulation in the floor joist bays.

I wasn't expecting that. Only trying to make the point the basement was already conditioned if there wasn't a thermal barrier between main floor and basement.

(Mostly UCF or Superior Walls around here.)