Heat loss and heat delivery are different problems
A room loses heat through its walls, ceiling, floor and windows, and through air leaking in and out. It gains heat from whatever the heating system delivers to it. A cold room can have a problem on either side. The U.S. Department of Energy's insulation guide for homeowners, Energy Renovations: Insulation, treats air sealing, insulation and ducts as separate parts of the same picture, and it's worth keeping them separate when you think about one room.
Air leaks and insulation gaps aren't the same thing
DOE's Consumer Guide to Air Sealing the Home explains that insulation slows the flow of heat but doesn't necessarily stop air from moving through cracks, holes and gaps. It compares insulation to a sweater that doesn't block the wind. Leaks around windows and doors are the obvious ones, but the guide notes there are often many smaller, less noticeable gaps, including between the attic and the rooms below. So adding insulation alone can leave a drafty room drafty.
Where the room sits matters. The insulation guide lists floors above an unconditioned basement, garage or vented crawlspace among common air-leak locations, suggests checking the insulation under floors over a garage, basement or crawlspace, and says cantilevered floors, such as bump-outs, bay windows or a room over an open porch, often lack proper air sealing and insulation in older homes. If your cold room is over a garage or porch, under an attic, or sticks out past the wall below, mention that to whoever assesses it. Opening up walls, ceilings or floors to check is a job for a qualified professional.
A cold window isn't always a leaky window
DOE's Measure Guideline: Energy-Efficient Window Performance and Selection describes two main ways windows make people uncomfortable in winter. Cold glass pulls radiant heat from your body, so you can feel chilly near a window even when the room air is at a comfortable temperature. And air next to cold glass cools, drops to the floor and sets up a draft. The guide says many people blame those drafts on leaky windows when they're actually caused by the cold window surface. Air leaks around a window are still possible, so ask an assessor to tell the difference before anyone recommends replacing windows. Our guide to why condensation forms on the inside of a window covers another sign of cold glass.
Ducts have to deliver heat and let air return
If you have forced-air heat, the insulation guide says leaky, poorly insulated ducts that run through unconditioned spaces such as an attic or crawlspace can lose a lot of energy, and that some rooms may be colder in winter because of heat lost along the ducts and air leaking at seams and joints, for example where branches meet a trunk line or where ducts meet registers. A room at the end of a long duct run through an unheated space is worth a closer look.
Air delivered to a room also needs a way back to the furnace. The Building America Solution Center's guide to ducted returns says inadequate return air pathways can cause pressure imbalances between rooms, leading to drafts and temperature differences between rooms or floors. It describes testing room pressure with all interior doors closed and the air handler running. So it's useful to note whether the room gets colder when its door is shut, but that's a clue, not a diagnosis. Let an HVAC professional measure airflow and pressure before anyone cuts doors or adds grilles.
What a professional energy assessment can check
DOE's Consumer Guide to Home Energy Assessments says the assessor should start with a walkthrough to see how energy is used, overall and in specific rooms. The two most common techniques are a blower door test, which depressurizes the house to measure air leakage and help find leaks, and an infrared scan, which shows temperature differences along walls, roofs, windows and doors. The guide recommends making sure the blower door is calibrated, since an uncalibrated one can spot leaks but can't measure how much air the house leaks. An assessor may also use a duct blower to measure leakage in the ductwork, inspect the heating and cooling system, test for natural gas leaks and check ventilation.
Air sealing has a safety side. DOE's air sealing guide says the first step is working out how much fresh air the home needs and making sure combustion appliances such as furnaces, stoves and fireplaces are properly vented, because without that, gases such as carbon monoxide can build up. It recommends a professional for sealing around flues and pipes connected to chimneys, furnaces and water heaters. Leave that work, and any equipment adjustments, to qualified professionals.
Bring notes, then ask for evidence
The assessment guide suggests listing indoor problems you've noticed, such as condensation and uncomfortable or drafty rooms, and having recent energy bills ready. For a cold room, it also helps to note when it feels coldest, where in the room it's worst, and whether the door is usually open or closed. Afterward, the assessor should give you a report of findings and ideas for improvements. Ask what evidence points to each cause, which repair addresses it, what's still uncertain, and how you'll know whether the fix worked for that room.
Philadelphia and Bucks County
To find a certified energy assessor, DOE's assessment guide suggests checking with your local electric or gas utility, your state or local energy or weatherization office, or ENERGY STAR's list of Home Performance with ENERGY STAR locations. If the same house also gets icicles or ice dams in winter, warm air reaching the attic may be part of the story; our guide to what causes ice dams and what fixes the cause explains the connection. Before you sign for insulation, duct or window work, our contractor hiring checklist for Philadelphia and Bucks County lists questions to ask.