You set the thermostat to 70.

The thermostat says 70.

Your feet say absolutely not.

Meanwhile, the furnace has been running long enough that you’re starting to wonder whether it has a side hustle with the utility company.

If your house feels cold even when the heat is running, turning the thermostat up another two degrees may help temporarily. It can also be the home-heating equivalent of solving a leaky bathtub by opening the faucet farther.

The real problem may be that the heat you’re paying for isn’t staying where you put it.

And while everybody immediately blames the windows, some of the biggest leaks in a house are hiding in places you rarely look.

ENERGY STAR specifically points to attics and basements as major hidden air-leak locations. Warm air escaping through the top of the house can also help pull cold outdoor air into lower portions of the house, creating what’s commonly called the stack or chimney effect.

Basically, your house can become a giant, extremely expensive chimney.

Let’s find the holes.

1. Your Attic Is Letting Heat Escape

If you’re trying to figure out where your heat is going, start looking up.

Warm air rises, and openings between your living space and attic give it plenty of escape routes.

Common trouble spots include attic hatches, plumbing penetrations, wiring holes, recessed lights, dropped soffits, duct chases and gaps where walls meet the attic floor.

ENERGY STAR recommends attacking the large air leaks first rather than obsessing over every microscopic crack.

That’s an important distinction.

If there’s a giant opening above a dropped soffit, spending Saturday afternoon carefully caulking a 1/16-inch crack around a window isn’t exactly maximizing your dad-hours.

Another clue is dirty attic insulation. ENERGY STAR notes that dirty insulation can indicate air has been moving through it.

What to check

Look around:

• Attic access doors and pull-down stairs
• Plumbing and electrical penetrations
• Recessed lights
• Bathroom fan penetrations
• Dropped soffits
• Chimney and flue penetrations
• Top plates and wall-to-ceiling transitions

And before you start foaming everything that looks suspicious, remember that heat-producing fixtures, flues and chimneys can require special clearances and fire-rated materials.

Expanding foam is useful.

Expanding foam is not holy water.

2. Your Rim Joists May Be Sneaking Cold Air Into the House

Go into an unfinished basement and look at the area where the top of the foundation meets the wooden framing of the house.

That’s rim-joist territory.

It also happens to be one of the places ENERGY STAR specifically identifies as a common source of basement air leakage.

Small gaps around the sill plate, rim joists and penetrations can allow outdoor air into the basement. Combine that with warm air escaping through the attic and you’ve created a nice little conveyor belt:

Warm air out the top.

Cold air in the bottom.

Furnace in the middle wondering what it did to deserve this.

ENERGY STAR recommends sealing gaps and cracks around rim joists, including the top and bottom of the cavity, and paying particular attention to penetrations for pipes, wires and ducts.

For smaller cracks, caulk may be appropriate. Larger gaps can require expanding foam or other suitable air-sealing materials.

If you’re already planning to finish a basement, this is the time to deal with it, not after you’ve covered everything with drywall and created a future treasure hunt.

3. An Uninsulated Basement Can Make the Floors Above It Miserable

Sometimes the problem isn’t a mysterious draft.

Sometimes there’s just a giant cold concrete box underneath your house.

Concrete isn’t insulation.

If your basement walls are uninsulated, heat can move through that foundation while the floor above the basement stays unpleasantly cold.

ENERGY STAR cites Building America guidance indicating that uninsulated basement walls can account for a substantial portion of a home’s heat loss. Air sealing and insulating basement walls can improve the thermal performance of the house while also making the basement more usable.

That matters even if you don’t particularly care whether the basement itself is cozy.

The basement ceiling is somebody else’s floor.

If the basement is freezing, your first floor gets invited to the party.

This is why basement insulation can be a comfort upgrade upstairs, not just part of a future basement-finishing project.

4. Your Ductwork May Be Heating Somewhere You Don’t Live

Your furnace can work perfectly and still fail to deliver all that warm air where you want it.

The ducts have to get it there.

According to ENERGY STAR, a typical home can lose roughly 20% to 30% of the air moving through its duct system because of leaks, holes and poorly connected ducts.

Twenty to thirty percent.

Imagine ordering five pizzas and the delivery driver eating one on the way over.

You’d have questions.

Yet we’ll happily let ductwork do essentially the same thing for years.

This is particularly important when ducts travel through unconditioned areas such as:

• Attics
• Crawlspaces
• Garages
• Unfinished basements

ENERGY STAR recommends sealing accessible duct seams and connections with mastic or metal-backed foil tape, not ordinary cloth “duct tape.”

Yes.

One of the few jobs for which duct tape is apparently not the preferred duct tape.

Marketing won that round.

5. Your Windows and Doors Really Might Be Leaking

Windows and doors get blamed for everything because they’re easy to feel.

And sometimes they absolutely deserve it.

Stand near a closed exterior door on a cold, windy day and you may be able to feel air entering around the perimeter.

Weatherstripping can help seal moving components such as doors and operable windows, while caulk is generally used for stationary gaps and cracks.

The good news is that these are often inexpensive fixes.

The bad news is that homeowners sometimes jump straight from “I feel a draft” to “I need $25,000 worth of new windows.”

Maybe.

But let’s spend $12 on weatherstripping before calling the window salesman.

A draft doesn’t automatically mean the entire window needs to be ripped out of the house.

6. Your Attic Insulation May Be Inadequate

Air sealing and insulation are related, but they’re not the same job.

Think of insulation as the winter coat and air sealing as zipping the coat.

You can keep piling insulation into an attic, but if heated air is freely moving through gaps underneath it, you haven’t solved the whole problem.

ENERGY STAR says that if attic insulation is at or below the level of the floor joists, the home probably needs more. It also emphasizes sealing attic air leaks because doing so improves the effectiveness of the insulation that’s already there.

This is why I’d investigate air leakage before blindly buying more insulation.

Otherwise you may spend a weekend adding fluffy material while the actual hole underneath it continues doing its thing.

7. Recessed Lights and Ceiling Penetrations Can Be Tiny Heat Escape Hatches

Every hole somebody cut through your ceiling deserves at least a little suspicion.

Recessed lights.

Electrical boxes.

Speaker wiring.

Plumbing.

Exhaust fans.

Duct chases.

It’s amazing how carefully we insulate an attic and then drill approximately 700 holes through the boundary between the house and attic.

One small opening isn’t necessarily dramatic.

Dozens of them add up.

ENERGY STAR specifically identifies recessed lighting, wiring holes, plumbing penetrations, open soffits and duct or furnace chaseways as common attic air-leak locations.

Just don’t start sealing around recessed lights without knowing what type you have. Some fixtures require clearance from insulation or special treatment.

Electricity is remarkably intolerant of enthusiasm without research.

8. Your Fireplace May Be Quietly Robbing You

A fireplace feels like it should make the house warmer.

When there’s an actual fire in it, sure.

When there isn’t, the chimney can become another path between conditioned indoor air and the outdoors.

Check that the damper closes properly when the fireplace isn’t being used, and inspect around the fireplace and chimney for obvious air-leak locations.

But this is also where DIY enthusiasm needs boundaries.

Combustion appliances, chimneys and flues aren’t places to improvise with whatever tube of sealant happens to be closest.

Use materials approved for the application and maintain required clearances.

The goal is a warmer house.

Not an exciting conversation with the fire department.

9. The Heating System Might Actually Be the Problem

After spending most of this article accusing your house of leaking, we should acknowledge the possibility that the furnace or heat pump itself isn’t performing properly.

A few warning signs:

• The system runs almost continuously
• Certain rooms never reach the thermostat setting
• Airflow from registers seems weak
• The temperature varies dramatically from room to room
• The equipment is older or hasn’t been serviced
• Filters are badly clogged
• Supply or return vents are blocked

But ENERGY STAR makes an important point: before replacing heating and cooling equipment, address major air leaks and duct problems because those may be the actual source of the comfort problem.

That’s worth remembering when someone tells you the solution is immediately spending $15,000 on new HVAC equipment.

Maybe it is.

Maybe your attic hatch is basically open.

Those are very different invoices.

How Do You Figure Out Where the Heat Is Actually Going?

Before buying insulation, windows, a furnace and enough spray foam to encase the house in a giant marshmallow, diagnose the problem.

Start with the free stuff.

Walk through the house on a cold or windy day.

Feel around exterior doors and windows.

Look for rooms that are consistently colder than others.

Check whether supply vents are open and unobstructed.

Inspect accessible ductwork.

Look around the basement rim joists.

Check the attic hatch.

Look at your attic insulation depth and condition.

If you want a more serious diagnosis, a home energy audit can be worthwhile. A professional energy auditor can use tools such as a blower door to depressurize the house and reveal air leakage that isn’t obvious during a walk-through. The Department of Energy specifically recommends energy audits as a way to identify the worst leakage points rather than guessing.

Thermal imaging can also help identify temperature differences, particularly when used under appropriate indoor/outdoor temperature conditions.

That’s considerably more useful than walking around the house pointing at things and saying, “Probably the windows.”

What Should You Fix First?

Don’t automatically start with the most expensive project.

I’d work roughly in this order:

Find the big air leaks.

Attic penetrations and basement/rim-joist leakage deserve particular attention because they’re major components of the stack effect.

Seal accessible leaks.

Weatherstripping, appropriate caulk and properly selected foam can solve some surprisingly annoying problems without requiring a home-equity loan.

Check the ducts.

Especially if they travel through an attic, crawlspace, garage or other unconditioned space.

Evaluate insulation.

Once you’ve reduced uncontrolled airflow, determine whether the attic, basement or other parts of the building envelope actually need more insulation.

Then evaluate the HVAC system.

If the house is reasonably sealed and insulated and still can’t maintain temperature, it’s time to look harder at the equipment, sizing, airflow and distribution.

That’s a much better strategy than replacing random expensive things until the house gets warmer or the checking account gets cold.

One Important Warning Before You Seal Everything

A tighter house is generally good for comfort and energy efficiency.

But there is such a thing as doing this badly.

ENERGY STAR warns that significant air sealing can affect combustion appliances and indoor air quality. Naturally vented gas or oil appliances can potentially backdraft if changes to the house affect how they receive combustion air or exhaust gases. A tighter home may also require proper mechanical ventilation.

If your project involves major air sealing and you have combustion equipment, fireplaces or other naturally vented appliances, professional combustion-safety testing is a very good idea.

Your house should be tight.

Your carbon monoxide detector should also be extremely bored.

Final Thoughts

If your house feels cold even though the thermostat says it shouldn’t, don’t immediately assume you need a bigger furnace.

Your heating system may be doing exactly what you asked.

Your house may simply be terrible at keeping the results.

Start at the top and bottom.

Check the attic for major air leaks.

Check the basement and rim joists.

Look at accessible ductwork.

Deal with obvious window and door drafts.

Then evaluate insulation and HVAC performance once you’ve stopped paying to heat parts of the property that don’t technically qualify as indoors.

And if the problem is just one family member who insists 72 degrees is “basically freezing”?

We already found a solution for that.

Give them one of our best heated blankets for 2026 and slowly back away from the thermostat.

The house gets fixed.

They get warm.

You get custody of the thermostat again.

Everybody wins.

Dad Approved.