air-qualityhvac
Our return vent for our hvac is right outside the master bedroom. The master bedroom gets very little airflow with the door shut.
It was recommended that we add secondary return duct in the master bedroom to combat the high static pressure that the house is under.
I have a question though, would it be beneficial to put a vent in the wall between the master bedroom and living room to help ventilate air in and out of the room so there is not as much pressure in the master bedroom?
Go to any big box store and get some 6" flexible insulated duct (this pic shows black sheathing on the outside, but it's often made of shiny reflective mylar):
And a couple of 6" boots, one for each end:
Use aluminum HVAC tape or a large band clamp or zip tie to connect the inner sleeve of the duct to the boots, then use another layer of tape to seal up the insulated layer and prevent it from sliding around. Cut holes in the ceiling to match the rectangular boot opening, keeping one long edge of each hole flush to a ceiling joist. Then take your duct assembly up into the attic and insert the boots into each hole. You can just leave the flexible duct lying on top of the ceiling joists. Back downstairs, use small nails (with heads, not finish nails) to nail through the inside of the boot opening into the side of the adjacent ceiling joist. Then install a couple of register grilles and you're done!
I would guess that modifying the duct work in a 1920s masonry construction home will be prohibitively destructive and involving removing or damaging irreplaceable trim that contributes to the building's character.
Mini split heat pumps:
An alternative, which will not be inexpensive but may be significantly less destructive, would be investigating installing a multi head mini split ac unit with one head in each bedroom. Such a unit costs perhaps $2500 to $5000 for the unit, installation extra and depends on the difficulty of install. If you live in a heating climate, especially one with cheap electricity in the winter or might install solar and have sunny winters, you should likely invest in the heat pump versions. Models are available that operate down to -13 F now (Mitsubishi M-Series) in single head. Supposedly multi-heads that operate that low are coming out this spring.
Advs:
Individual temperature control for each bedroom - Really high efficiency available for both heating and cooling - Avoid destruction of interior trim
Disads: - Potentially a lot of $$$ - Still a newer technology in the US (used all over Europe and Japan). If you plan to sell soon, recovering your investment at resale could be a challenge - Some people hate the look.
Other than minisplits:
Air leakage:
I'd suggest you have a blower door test performed. All the insulation in the world doesn't matter if you are changing over the air in the house too quickly. If you didn't air seal the attic before filling it with cellulose, you could have this problem. An infrared gun on a cold night can help show these leaks too. Insulation installers will say things like seals in air but cellulose, fiberglass insulation, and mineral wool insulation are actually very air permeable. If you find that is the problem, you could move insulation out of the way in the attic to use canned foam (get a commercial gun, much nicer job to do than with home depot cans). If you can't move the insulation, you could install a vapor permeable sheet membrane like Tyvek or a smart vapor retarder like IntelloPlus on top of the insulation to block air movement. Do not use a vapor impermeable barrier like black plastic or visqueen (clear plastic); you could trap moisture and cause a mold problem. Attic access hatches are also causes of large volume air leaks. There are special hatch covers you can buy or build to address this problem.
Duct work in unconditioned space:
Do you have any ducts in unconditioned (uninsulated) space like an open crawl space or an unconditioned attic? If so, you could be losing huge amounts of heat to the crawl space or attic. If your ducts are older, they likely aren't air tight either. You could use specialized foil tape or duct mastic to seal the joints and you could insulate this duct work, though it won't be fun work. If your ducts are really leaky, you could get big gains in system performance from this work.
Humidity control:
Have you measured your humidity when your system is running? If your humidity is high in the winter or summer, you will feel colder or hotter. Your humidity could be high in the house for many reasons (improper shower venting) but dirt crawl spaces are a big source in the summer (not in the winter so much). Seal off the dirt crawl space to eliminate humidity, mold spores, radon, etc. from getting in the house. A radon membrane company, in areas with radon, might be a cost effective contractor to use.
Best Answer
Yes, adding a transfer grille or jump duct will be the easiest and most effective solution. It can be done in a way to minimize transfer of sound between rooms (see links below). Adding a return to the master bedroom doesn't guarantee that the supply/return to the master bedroom will become balanced—the resulting pressure may still be positive or even negative with respect to the rest of the house.
http://www.buildingscience.com/documents/information-sheets/information-sheet-transfer-grilles-and-ducts/
https://basc.pnnl.gov/resource-guides/transfer-grilles