Prep Your Home for Missouri's Hot Summers

If you’ve lived through one Missouri summer, you know the drill. The heat index cracks 110, your A/C runs 18 hours a day, afternoon thunderstorms roll in like clockwork, and the humidity turns your garage into a sauna. That’s not a freak occurrence — that’s July.

Your house takes the brunt of it. And every year, I get calls from homeowners who hit mid-summer with an HVAC failure, a flooded basement, or a deck that’s splintering under their feet. Most of those calls could’ve been prevented with a weekend of prep work in April or May.

Here’s the checklist I use for my own house and recommend to every customer.

HVAC: Your Most Important System from May to September

The U.S. Department of Energy estimates that heating and cooling account for about 43% of a typical household’s energy costs. In Missouri, I’d guess cooling skews even higher because of how hard our systems work during summer. Your A/C isn’t a luxury here — it’s infrastructure.

Get It Serviced Before You Need It

Schedule a professional HVAC tune-up in April. Not June. In June, every HVAC company in St. Charles County is booked solid and charging premium rates for emergency calls.

A proper tune-up includes checking refrigerant levels, cleaning the evaporator and condenser coils, inspecting the blower motor, testing electrical connections, and clearing the condensate drain. That drain, by the way, is a common failure point — if it clogs in July, your system shuts down or, worse, overflows and damages your ceiling or walls.

Change Filters Monthly — Actually Monthly

I know you’ve heard this before. I know you’re still running a three-month filter from January. Change it. During peak cooling season (May through September), change your HVAC filter every 30 days. A clogged filter restricts airflow, forces the system to work harder, raises your energy bill, and shortens the compressor’s lifespan.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends filter replacement intervals based on usage, and peak summer in Missouri qualifies as heavy usage by any standard.

Clear the Outdoor Unit

Your condenser unit — the big box outside — needs airflow. Walk out and look at it. Is it surrounded by landscaping? Buried in mulch? Covered in cottonwood seeds? (If you live anywhere near the Missouri River bottoms or mature cottonwood trees, you know the nightmare.)

Clear at least two feet of space around all sides of the unit. Rinse the fins gently with a garden hose — from the inside out if you can. Don’t use a pressure washer; those fins bend easily and bent fins block airflow.

Seal the Envelope: Weatherstripping and Caulk

It seems counterintuitive to think about air sealing when you’re prepping for heat, but air leaks work both ways. Every gap that lets cold air escape in winter lets hot, humid air infiltrate in summer. And infiltrating humidity makes your A/C work harder and can lead to condensation issues inside walls.

Check Weatherstripping on All Exterior Doors

Open each exterior door and look at the weatherstripping along the sides and top. Close the door and check for daylight around the edges. If you can see light, air is getting through.

Replacing weatherstripping is a straightforward DIY job. Peel-and-stick foam tape works for a quick fix, but V-strip (tension seal) weatherstripping lasts longer and seals better. The U.S. Department of Energy’s weatherization guidelines recommend V-strip for door frames specifically because of its durability.

Inspect and Replace Exterior Caulk

Walk the outside of your house and check the caulk around every window frame, door frame, and penetration (electrical boxes, faucets, vents). Missouri’s freeze-thaw cycles destroy caulk faster than most climates. If it’s cracked, shrunk, or missing, scrape it out and reapply.

Use a polyurethane or silicone-based exterior caulk rated for at least -20 to 150 degrees Fahrenheit. The cheap stuff won’t hold up through a Missouri summer-to-winter cycle.

If you’re not sure about the condition of your home’s sealing, we offer general maintenance assessments that cover all of this.

Gutters and Drainage: Your Storm Defense

St. Louis averages about 42 inches of rainfall per year, according to the National Weather Service office in St. Louis. A lot of that falls in concentrated bursts during summer thunderstorms. Your gutters and drainage are the system that keeps all that water moving away from your house.

Clean the Gutters

Yes, again. Even if you cleaned them in November. Spring storms, wind-blown debris, and those whirlybird seed pods from silver maples can clog gutters by April. One blocked downspout during a summer storm sends water cascading over the edge and pooling against your foundation.

Check Downspout Extensions

Every downspout should discharge water at least four feet from the foundation — six feet is better. Extensions get kicked, mowed over, or removed and never replaced. Walk the perimeter and make sure every one is in place and directing water away from the house.

Test the Sump Pump

If you have a basement, test your sump pump now. Pour five gallons of water into the pit and verify it kicks on, pumps the water out, and shuts off cleanly. If it struggles, runs but doesn’t move water, or doesn’t start at all, replace it before storm season.

Battery backup sump pumps are worth the investment in this area. A power outage during a heavy thunderstorm is the worst time to discover your primary pump can’t run.

Deck Maintenance: Prep It or Lose It

Missouri summers are hard on decks. UV radiation breaks down the surface finish. Rain saturates the wood. Humidity keeps it damp. And then the next sunny day bakes it again. That wet-dry cycle is what causes warping, splitting, and premature rot.

Inspect Before You Stain or Seal

Before you crack open a can of stain, check the structural integrity of your deck. Walk every board and feel for soft spots. Push on every railing post. Look at the ledger board where the deck connects to your house — water infiltration at the ledger is the number one cause of deck failures, according to the North American Deck and Railing Association.

Check the fasteners too. Popped nails and backed-out screws create trip hazards and let water into the wood. Replace any that have pulled out.

Stain or Seal Every Two to Three Years

Bare wood exposed to Missouri weather has a limited lifespan without protection. The Forest Products Laboratory (part of the USDA Forest Service) recommends reapplying exterior wood finishes every one to three years depending on exposure, with south-facing and west-facing surfaces needing more frequent attention.

If your deck hasn’t been stained or sealed in three or more years, this spring is the time. Power-wash it first (carefully — too much pressure damages wood fiber), let it dry for 48 hours, and apply a penetrating stain or sealant.

For a deeper dive on whether your deck needs repair, staining, or full replacement, check out our deck season guide.

Windows and Screens

Install or Repair Window Screens

If you plan to open windows during the milder parts of summer — early mornings, late evenings — you need screens that actually work. Torn screens let in mosquitoes, and the St. Louis metro area is well within the range for mosquito-borne diseases flagged by the Missouri Department of Health and Senior Services.

Replacing screen mesh in an existing frame is a $10 DIY project with a spline roller and new screening material. If the frames themselves are damaged, replacements are available at most hardware stores for standard window sizes.

Check Window Locks and Operation

Windows that don’t close and lock properly are a security issue and an energy issue. Test every window in the house. If a window is stuck painted shut, carefully score the paint line with a utility knife and work it free. Windows that won’t stay up need new balance mechanisms — a common issue in the single-hung windows typical of 1970s and 1980s construction across West County and South County.

Exterior Inspection: 30 Minutes That Save Thousands

Take a slow walk around your house with a notepad. Look at:

Siding and trim: Check for peeling paint, cracks, gaps, or signs of pest damage. Carpenter bees are active in Missouri from April through June and will bore into untreated wood siding, fascia, and deck railings.
Foundation: Look for new cracks or changes in existing ones. Photograph them for comparison later.
Grading: Soil should slope away from the foundation. If landscaping or erosion has created flat spots or negative drainage, add soil to rebuild the slope before summer rains.
Dryer vent: Check that the exterior flap opens freely and isn’t blocked by lint or debris. A blocked dryer vent is a fire hazard year-round, but a dryer running hot in an already-hot house is extra risk.

The Attic: Out of Sight, Not Out of Mind

Your attic temperature in a Missouri summer can exceed 150 degrees. That heat radiates through the ceiling into your living space and makes your A/C work overtime.

Check Attic Ventilation

Proper attic ventilation requires intake (usually soffit vents) and exhaust (ridge vents, gable vents, or power vents). If your soffit vents are blocked by insulation that’s been pushed against them, pull it back or install baffles. The International Residential Code calls for a minimum of 1 square foot of net free ventilation area for every 150 square feet of attic floor — or 1:300 if you have balanced intake and exhaust.

Inspect Insulation

While you’re up there, check the insulation depth. The Department of Energy recommends R-38 to R-60 for attics in Climate Zone 4 (which covers the St. Louis region). That translates to roughly 10 to 14 inches of fiberglass batts or 8 to 11 inches of blown cellulose. If you can see the ceiling joists, you don’t have enough insulation, and you’re paying for it every month from June through September.

Make the List, Check It Twice

Here’s a one-page version you can print:

You don’t have to do all of this in one weekend. Spread it over two or three weekends in April and May. The goal is to have everything buttoned up before the heat and storms hit in earnest.

And if you’d rather hand the list to someone else, that’s what we’re here for. Get in touch and we’ll knock it out so you can spend your summer on the deck instead of under the house.

How to Prep Your Home for Missouri's Brutal Summers