The Household Numbers: Right Settings, Not Factory Defaults

Quick reference

The settings card

Use this first. The detailed panels below explain the tradeoffs.

System	Right number	Verify with	Factory/default trap
Water heater delivery	120°F / 49°C at the tap, or 140°F / 60°C storage with a thermostatic mixing valve	Probe thermometer after a long draw	140°F reduces microbial risk but sharply increases scald risk.
Refrigerator	35-38°F / 1.7-3.3°C, always at or below 40°F / 4°C	Appliance thermometer, 24 hours	Unnumbered dials measure coldness, not temperature.
Freezer	0°F / -18°C	Freezer thermometer	Colder costs energy; warmer accelerates quality loss.
Dishwasher	120°F / 49°C hot-water inlet; scrape, do not pre-rinse	Sink thermometer near dishwasher	Pre-rinsing wastes water and can hurt detergent performance.
Indoor humidity	30-50% RH; keep below 60%; winter cold-climate target often 30-40%	$10-50 hygrometer	45% in deep winter can condense on cold windows/walls.
Thermostat setback	7-10°F for about 8 hours can save up to ~10%/yr	Thermostat schedule plus bill trend	Heat pumps may need gentler setbacks to avoid resistance heat.
HVAC filtration	MERV 13 if the system can handle it; otherwise the highest rated filter that maintains airflow	Manual, filter slot, static-pressure pro if unsure	Higher MERV is not always better in a weak residential blower.
CO2 ventilation proxy	Prefer <1,000 ppm during occupancy	NDIR CO2 monitor	CO2 is a ventilation proxy, not a complete IAQ test.
Radon	Fix at 4 pCi/L / 150 Bq/m3 or higher; consider 2-4 pCi/L	Short-term or long-term radon kit	You cannot smell or feel it.
Smoke alarms	Test monthly; replace alarm at 10 years	Date on back of alarm	Fresh batteries do not reset an expired sensor.
CO alarms	Install near sleeping areas; replace by maker date, commonly 5-10 years	Date label and test button	UL-style alarms are not low-level health monitors.
Tires	Vehicle placard cold PSI, not sidewall max	Quality tire gauge, monthly/cold	TPMS may wait until roughly 25% low.
Water pressure	40-60 psi normal; investigate >80 psi	Hose-bib pressure gauge	High pressure feels nice and wears fixtures.
Garage door	Monthly 2x4 reverse test; photo eyes 4-6 in above floor	2x4 and visual sensor check	A moving door is not proof the safety reverse works.
Car battery	~12.6 V rested is healthy; <12.4 V wants charging/testing	Multimeter after resting	A battery can start today and fail under cold load tomorrow.
Router	Central, elevated, visible; 5 GHz for speed, 2.4 GHz for reach	Wi-Fi analyzer or speed test	Buying a faster router cannot fix bad placement.
Backups	3 copies, 2 devices/media, 1 offsite; test restores	Restore a file quarterly	Sync is not backup if deletion syncs too.

Verify, do not trust dials

The $60-ish household instrument kit

Appliance thermometer

Use one in the fridge and one in the freezer for 24 hours before changing the dial again.

Probe thermometer

Measure hot tap water, dishwasher inlet temperature, and actual oven calibration checks.

Hygrometer

Place it where you live, not in a closet. Check winter windows for condensation.

Tire gauge

Check cold tires monthly and before long trips. TPMS is a late warning.

Pressure gauge

Thread a $10 hose-bib gauge onto an outdoor spigot to find pressure-regulator problems.

Radon kit

A short-term kit screens; a long-term test is better for the annual-average decision.

Water systems

Hot water, pressure, freezing, and shutoffs

120°F tapor 140°F storage + mixing valve

What temperature should my water heater be?

NumberFor most homes, deliver 120°F / 49°C at taps. If Legionella risk is high, store at 140°F / 60°C and install a thermostatic mixing valve delivering about 120°F.

DefaultMany tanks arrive near 140°F because hot storage reduces microbial risk and service complaints; it also makes scalds happen much faster.

EvidenceCPSC says third-degree burns can occur after about 5 minutes at 120°F, 30 seconds at 130°F, and 6 seconds at 140°F. CDC water-system control guidance uses hot storage above 140°F and circulation above 120°F for Legionella control.

Tradeoff120°F cuts scald and standby-loss risk; 140°F storage is a microbial-control choice for high-risk occupants, large plumbing runs, or recirculation systems.

VerifyRun hot water until stable, measure at the tap, adjust slowly, and recheck after 24 hours. For electric tanks, kill power before opening access panels.

CPSC scalds CDC Legionella DOE/Energy Saver

40-60 psi>80 psi is a fixture-wear flag

What water pressure should a house have?

NumberMost homes are comfortable around 40-60 psi; sustained pressure above 80 psi deserves a pressure regulator check.

DefaultMunicipal pressure is set for the neighborhood, not your valves, toilet fill seals, water heater, and ice-maker tubing.

EvidenceResidential plumbing codes commonly require pressure-reducing valves when supply pressure exceeds 80 psi; manufacturers often design fixtures for lower operating pressure.

TradeoffHigh pressure makes showers feel strong but increases leaks, water hammer, appliance valve wear, and wasted flow.

VerifyAttach a hose-bib gauge, test with no water running, then again during a fixture draw. If it creeps overnight, suspect thermal expansion or a regulator issue.

Set grainsfrom a hardness test, not a guess

What should my water softener hardness be set to?

NumberSet the softener to measured hardness in grains per gallon, adding iron compensation if your manual specifies it.

DefaultInstaller guesses and factory defaults waste salt or leave scale because hardness varies by city, well, and season.

EvidenceHardness is a measured water-quality input; the right setting is not universal. See the filtration sheet for water-testing depth.

TradeoffToo low leaves scale; too high regenerates too often and adds sodium/potassium load.

VerifyUse a drop-count hardness kit upstream and downstream of the softener after regeneration.

Air & Water Filtration

~20°F outsiderisk threshold, not magic

When should I drip faucets to prevent freezing?

NumberWhen outdoor temperatures approach the teens/low 20s °F, prioritize exterior-wall pipes, unheated crawlspaces, and windy sides of the house.

DefaultThe folklore number ignores insulation, wind, pipe location, and how long the cold lasts.

EvidenceFreeze risk rises when vulnerable pipes stay below freezing long enough for ice expansion; local utilities often use about 20°F as a public warning threshold.

TradeoffDripping wastes water; a burst pipe costs far more. Open cabinet doors first when supply lines are on exterior walls.

VerifyKnow the main shutoff and label it. The shutoff location is the one non-number that belongs on this page.

2 tests/yrbefore wet seasons

How often should I test a sump pump?

NumberTest before spring storms and before fall/winter precipitation; monthly if your basement depends on it.

DefaultSump pumps fail quietly because the only normal signal is absence of a flood.

EvidenceMechanical float switches, check valves, and discharge lines are wear points; preventive testing is more reliable than calendar optimism.

TradeoffBattery backups need their own battery replacement schedule; a dry pump can still fail under storm load.

VerifyPour water into the pit until the float rises. Confirm pump start, shutoff, and outdoor discharge.

<30 secto find and close

How fast should I be able to shut off house water?

NumberEvery adult in the home should be able to find and close the main water shutoff in under 30 seconds.

DefaultBuilders hide shutoffs in basements, crawlspaces, garages, utility closets, or meter boxes with no label.

EvidenceFor burst hoses, failed toilet valves, and split ice-maker lines, response time controls damage.

TradeoffA stuck old gate valve may snap; exercise gently and replace with a quarter-turn ball valve during planned plumbing work.

VerifyTag the valve, photograph it, and store the photo in your home folder.

Kitchen cold & heat

Food safety numbers and appliance lies

35-38°FFDA ceiling: 40°F / 4°C

What temperature should my refrigerator be?

NumberTarget 35-38°F so door openings do not push food above the FDA 40°F ceiling.

DefaultDial numbers like 1-7 are not degrees; they are compressor-control hints shaped by energy-label and noise tradeoffs.

EvidenceFDA says refrigerators should be at 40°F or below and recommends appliance thermometers because controls rarely show true temperature.

TradeoffToo warm risks spoilage; too cold freezes lettuce, eggs, and back-wall items.

VerifyPut a thermometer near the middle shelf, wait 24 hours, then adjust one notch at a time.

FDA fridge

0°F-18°C

What temperature should my freezer be?

NumberSet the freezer to 0°F / -18°C.

DefaultFreezers are often set colder than needed to mask warm-door recovery or warmer than needed to save energy.

EvidenceFDA uses 0°F as the freezer safety target; colder mainly protects quality, not safety, after food is already frozen.

TradeoffColder increases energy and frost; warmer shortens quality life and softens ice cream.

VerifyUse a freezer thermometer and check after a full compressor cycle, not immediately after loading groceries.

FDA storage

Warmest zonedoor shelves

Should milk go in the refrigerator door?

NumberKeep high-risk perishables in the colder body of the fridge, not the door; use the door for condiments and resilient drinks.

DefaultDoor bins are designed for convenient storage and showroom capacity, not the coldest temperatures.

EvidenceThe door experiences the largest warm-air swings whenever opened; the FDA ceiling still applies to the food, not the dial.

TradeoffMoving milk inward costs space but buys temperature stability.

VerifyPut one thermometer in the door and one mid-shelf for 24 hours; the difference usually settles the argument.

120°F inletscrape, do not pre-rinse

What temperature should dishwasher water be?

NumberGive the dishwasher about 120°F / 49°C inlet water and run full loads; scrape plates instead of pre-rinsing.

DefaultPeople pre-rinse because old dishwashers were weak and because clean-looking dishes feel virtuous.

EvidenceENERGY STAR consumer guidance says full loads matter and scraping instead of rinsing saves water and energy.

TradeoffVery cold inlet water makes the machine heat longer; very hot storage increases scald risk elsewhere.

VerifyRun the nearby sink hot, measure temperature, then start the cycle. Clean the filter if dishes emerge gritty.

ENERGY STAR

±25°Fdrift is common enough to test

How do I know if my oven temperature is accurate?

NumberCheck at 350°F with an oven thermometer; many ovens cycle around the setpoint and can be off by 25°F or more.

DefaultThe panel shows the requested temperature, not continuous cavity temperature.

EvidenceOvens use cycling thermostats and hidden calibration offsets; food doneness should be verified by internal temperature.

TradeoffChasing instant readings causes overcorrection. Average several cycles.

VerifyPut a thermometer in the center, preheat fully, log 3-4 cycle peaks/lows, then use the calibration-offset menu if your manual allows.

145/160/165°F food thermometer anchors

What meat temperatures should I remember?

NumberUSDA anchors: whole cuts of beef/pork/lamb 145°F plus 3-minute rest, ground meats 160°F, poultry 165°F.

DefaultColor and juice clarity are unreliable safety indicators.

EvidenceUSDA FSIS publishes the safe minimum internal temperature chart.

TradeoffThis page is not a cooking guide; use the temperature anchors and move detailed technique to a kitchen sheet.

VerifyMeasure the thickest part, away from bone, fat, or gristle.

USDA chart Cooking Guide

Air & climate

Humidity, filtration, ventilation, and thermostat numbers

<30% dry30-50% target>60% mold risk

30-50% RHbelow 60%; winter often 30-40%

What indoor humidity should I keep?

NumberEPA says keep indoor humidity below 60%, ideally 30-50%. In cold climates, start around 30-40% in winter and reduce if condensation appears.

DefaultHumidifier dials often chase comfort without seeing cold-window condensation or hidden wall temperatures.

EvidenceEPA mold guidance ties high humidity to mold and recommends a moisture/humidity meter.

TradeoffLow RH dries skin and wood; high RH feeds mold, dust mites, and condensation damage.

VerifyMeasure in bedrooms/living areas, not next to the humidifier. Check north-facing windows during cold snaps.

EPA mold

7-10°Ffor 8 hours

Does turning the thermostat down really save energy?

NumberDOE says a 7-10°F setback for 8 hours a day can save as much as about 10% per year on heating and cooling.

DefaultThe myth is that reheating costs more than the setback saves. For most conventional systems, lower temperature difference wins.

EvidenceDOE Energy Saver uses the 7-10°F / 8-hour rule of thumb.

TradeoffHeat pumps may trigger resistance/aux heat after aggressive setbacks; use smaller setbacks or smart recovery if that happens.

VerifyWatch runtime and aux-heat indicators for a week after changing schedules.

DOE guide

65-68°Fbedroom starting point

What bedroom temperature is best for sleep?

NumberUse 65-68°F / 18-20°C as a starting range, then tune for bedding, age, and partner comfort.

DefaultWhole-home thermostat comfort often leaves bedrooms warmer than sleep preference after doors close.

EvidenceSleep-temperature evidence supports avoiding hot bedrooms; the site sleep sheet covers the details.

TradeoffToo cold fragments sleep for some people. Bedding insulation matters as much as air temperature.

VerifyMeasure at mattress height for a week, not at the hallway thermostat.

Sleep Optimization

MERV 13if your system can handle it

What HVAC filter MERV should I use?

NumberEPA says MERV 13 or higher can trap smaller particles; use MERV 13 or the highest rating your fan and filter slot can accommodate.

DefaultMany systems ship with or are maintained around MERV 8 because it is cheap and low restriction.

EvidenceEPA explicitly warns to choose what the system can accommodate; higher restriction can reduce airflow.

TradeoffMERV 16 in a typical residential return can choke airflow, ice coils, or overheat furnaces.

VerifyCheck monthly and change when visibly loaded or pressure/airflow drops. Calendar-only intervals are marketing.

EPA MERV Filtration depth

<1,000 ppmventilation proxy

What indoor CO2 level is too high?

NumberUse about 1,000 ppm as a practical ventilation flag in occupied rooms, not as a toxicity threshold.

DefaultHomes rarely show ventilation status unless you measure it.

EvidenceNIOSH health-hazard evaluations use elevated indoor CO2 around this range as a sign that ventilation may be inadequate.

TradeoffCO2 does not measure PM2.5, VOCs, humidity, or combustion gases.

VerifyUse an NDIR CO2 monitor away from your breath plume; open a window or run ventilation and watch decay.

NIOSH HHE

4 pCi/L150 Bq/m3 action level

What radon level requires action?

NumberEPA recommends fixing homes at 4 pCi/L or higher and considering action between 2 and 4 pCi/L.

DefaultRadon is ignored because it has no smell, no immediate symptom, and no appliance dial.

EvidenceEPA's action level is the US reference point for home radon decisions.

TradeoffShort-term tests are convenient but weather and house operation affect readings; long-term tests better estimate annual exposure.

VerifyTest the lowest lived-in level. Do not place kits in kitchens, bathrooms, or drafts.

EPA radon

Safety numbers

Alarms, fire, doors, leaks, and fall-risk settings

10 yearsreplace smoke alarm unit

How often should smoke alarms be replaced?

NumberTest monthly and replace the alarm unit at 10 years, even if batteries still work.

DefaultPeople replace batteries and assume the sensor is immortal.

EvidenceUS fire-safety guidance consistently uses 10 years for smoke-alarm replacement.

TradeoffHardwired alarms still have sensors and backup batteries; hardwired does not mean permanent.

VerifyTwist the alarm down and read the manufacture/replace-by date on the back.

5-10 yearsfollow replace-by date

How often should carbon monoxide alarms be replaced?

NumberReplace by the manufacturer's date, commonly 5-10 years; install near sleeping areas and on levels with fuel-burning appliances.

DefaultA silent alarm does not prove zero CO; consumer alarms are designed for acute alarm thresholds, not low-level chronic monitoring.

EvidenceOSHA's workplace CO limit is 50 ppm as an 8-hour average; home alarms are a last-line warning, not an appliance-tuning tool.

TradeoffLow-level monitors can help vulnerable households, but the fix for CO is combustion service and ventilation, not alarm shopping.

VerifyCheck date label, test button, and battery. Service fuel-burning appliances annually.

OSHA CO

ABC + greengauge in operable zone

What fire extinguisher should a house have?

NumberUse accessible ABC extinguishers with the pressure gauge in the operable/green zone; inspect visually monthly.

DefaultExtinguishers are bought once, placed behind clutter, and forgotten until the gauge has leaked down.

EvidenceFire-safety inspection practice emphasizes correct type, access, and pressure condition.

TradeoffExtinguishers are for small, contained fires with a clear exit behind you. Evacuate if in doubt.

VerifyCheck gauge, pin, hose, corrosion, and location. Teach PASS only after everyone knows when not to fight a fire.

1x/yearmore if drying slows

How often should I clean the dryer vent?

NumberClean lint screen every load and inspect/clean the vent at least annually; do it sooner if loads take longer or the dryer runs hot.

DefaultThe lint screen catches only part of the lint; the hidden duct is the failure path.

EvidenceUSFA fire-prevention material identifies dryer lint and appliance maintenance as home-fire concerns.

TradeoffFlexible foil ducts crush and trap lint; short, smooth metal ducting is safer and dries faster.

VerifyCheck exterior flap airflow during a cycle and remove lint from the duct run.

USFA fire

2x4 testevery 30 days

How do I test a garage-door auto reverse?

NumberCPSC says inspect every 30 days: place a 2x4 in the door path; the door must reverse when it hits. Photo eyes should be about 4-6 inches above the floor.

DefaultOpeners can lift and close while the safety reverse is misadjusted or the photo eyes are defeated.

EvidenceCPSC requires reversing systems on post-1991 openers and gives the 2x4 test.

TradeoffIf it fails, disengage the opener and repair or replace it; do not tune force upward to mask a binding door.

VerifyAlso check door balance manually with the opener released.

CPSC garage

$10-20 sensorsat high-loss points

Where should water leak sensors go?

NumberPut sensors at the water heater, washing machine, dishwasher, under sinks, refrigerator ice-maker line, sump pit, and lowest finished basement point.

DefaultSupply hoses and valves fail behind appliances where nobody looks.

EvidenceWater damage is controlled by detection time; a cheap alarm near the failure point changes response time from hours to minutes.

TradeoffBattery alarms are local; smart sensors add notification but depend on Wi-Fi and app maintenance.

VerifyTouch probes with a wet finger twice a year and replace batteries on a schedule.

Garage & outdoors

Tires, batteries, hoses, grills, and outdoor edge cases

Door placardcold PSI

Should I use tire sidewall pressure or door-jamb pressure?

NumberUse the vehicle placard cold inflation pressure on the driver's door jamb or manual. The sidewall number is a maximum, not the setting.

DefaultThe sidewall is visible and authoritative-looking, so people use the wrong number.

EvidenceNHTSA TireWise points drivers to proper tire pressure and FMVSS 138 requires TPMS warning at 25% or more below placard pressure.

TradeoffUnderinflation overheats tires and wastes fuel; overinflation can reduce grip and wear the center.

VerifyCheck monthly when tires are cold. Expect about 1 psi change per 10°F seasonal temperature swing.

NHTSA TireWise FMVSS 138

12.6 Vrested lead-acid reference

What car battery voltage is healthy?

NumberAbout 12.6 V after resting is fully charged for a typical 12 V lead-acid battery; below about 12.4 V suggests partial charge or testing need.

DefaultStarting once is not a battery test; cold weather exposes weak reserve capacity.

EvidenceOpen-circuit voltage is a rough state-of-charge proxy; load testing is the real diagnosis.

TradeoffSurface charge can mislead right after driving. Let it rest or turn headlights on briefly before measuring.

VerifyUse a multimeter at the posts, then follow up with a load test if it is low or older than 4-5 years.

Auto Repair Decoder

<50°F ambientgarage fridge warning

Why does a garage refrigerator fail in winter?

NumberMany single-thermostat refrigerators behave badly below roughly 50°F ambient unless rated for garage use.

DefaultThe fridge senses cold room air, runs less, and the freezer can warm while the fresh-food compartment looks fine.

EvidenceAppliance operating-temperature ranges are model-specific; garage-ready units use different controls/heaters.

TradeoffA garage kit may help some models; for food safety, thermometer data beats assumptions.

VerifyPut thermometers in both compartments during the first cold snap.

Before freezedisconnect hoses

When should outdoor hoses be disconnected?

NumberDisconnect hoses before the first hard freeze and shut off/drain interior hose-bib valves where present.

DefaultFrost-free spigots still split if a hose traps water in the barrel.

EvidenceFreeze damage comes from trapped expanding water, not from the handle position alone.

TradeoffCovers help exposed fixtures, but they do not fix a hose left attached.

VerifyAfter disconnecting, tilt hose ends down and confirm the bib drains.

10 ftclearance is the simple rule

How far should a grill be from the house?

NumberUse 10 ft from siding, railings, eaves, and combustible clutter as the conservative residential habit unless your manual is stricter.

DefaultDeck convenience pulls grills under eaves and against vinyl siding.

EvidenceFire-safety guidance emphasizes keeping grills outdoors and away from structures and combustibles.

TradeoffWind and traffic paths matter; do not move a hot grill to solve rain.

VerifyMeasure once and mark the safe patio spot.

Monthlyoil level check

How often should I check engine oil level?

NumberCheck monthly and before long trips, even if the oil-change interval is much longer.

DefaultMaintenance mindshare focuses on oil age, but many engines die from low level between changes.

EvidenceOwner's manuals specify the exact oil grade and check method; the universal habit is verifying level on schedule.

TradeoffOverfilling can be harmful. Add in small increments.

VerifyPark level, wait per manual, wipe dipstick, reinsert, read, and log consumption.

Car maintenance

Digital & electrical

Router placement, backup cadence, surge protection, and breaker reality

Central + highplacement beats settings

Where should a Wi-Fi router go?

NumberPlace it central, elevated, and in open air. Use 5 GHz/6 GHz for speed nearby and 2.4 GHz for range/IoT.

DefaultISPs install routers where the cable enters, often a corner, basement, closet, or metal cabinet.

EvidenceRadio link budget is dominated by distance, walls, metal, and interference before advanced settings matter.

TradeoffMore transmit power can increase interference; mesh backhaul placement matters more than the app's speed claim.

VerifyRun speed/latency tests at problem seats before and after moving the router.

Load <50%if runtime matters

How much UPS runtime do I really have?

NumberKeep critical loads under about half of UPS rated capacity if you want useful runtime; replace batteries when self-test or age says so.

DefaultVA ratings look bigger than watts and runtime curves collapse at high load.

EvidenceUPS runtime is a battery curve, not a single advertised number.

TradeoffUPS is for graceful shutdown and networking continuity, not running heaters, laser printers, or refrigerators.

VerifyPull AC during a maintenance window and time the real load.

Replace after hitjoules are consumable

Do surge protectors wear out?

NumberReplace plug-in surge strips after a major surge, failed indicator light, physical damage, or roughly several years of uncertain service.

DefaultPower strips look permanent; the MOV protection inside is sacrificial.

EvidenceSurge energy ratings are finite. Whole-house surge protection plus point-of-use strips is better than old strips alone.

TradeoffA cheap strip is not a substitute for grounded wiring.

VerifyCheck protection/ground lights and replace mystery strips from prior homes.

80%continuous-load rule of thumb

Can I run a circuit at breaker rating?

NumberDo not plan continuous loads above 80% of circuit rating: about 12 A on a 15 A circuit or 16 A on a 20 A circuit.

DefaultThe breaker number is a protection limit, not a target operating load.

EvidenceElectrical codes size continuous loads with margin; exact applications require an electrician.

TradeoffSpace heaters, EV charging, and crypto/mining loads expose weak outlets and shared circuits.

VerifyMap outlets to breakers and use a plug-in power meter for appliances. Call an electrician for heat, buzzing, discoloration, or nuisance trips.

Top at eyemonitor baseline

How high should my monitor be?

NumberSet the top of the main screen around eye level, about an arm's length away, with elbows near 90 degrees.

DefaultLaptop screens are too low when used for hours.

EvidenceErgonomic guidance converges on neutral neck, supported arms, and avoiding glare.

TradeoffProgressive lenses may need lower screens; comfort beats rigid geometry.

VerifyWork for 30 minutes and check whether your chin is jutting or shoulders are raised.

3-2-1plus restore test

What is the minimum backup rule?

NumberKeep 3 copies, on 2 different devices/media, with 1 offsite/cloud copy. Test restoring a real file quarterly.

DefaultCloud sync feels like backup until deletion, ransomware, or account lockout syncs too.

EvidenceRedundancy only counts when failure modes differ and restore is proven.

TradeoffVersioned backup costs more than sync but protects against mistakes.

VerifyRestore a tax PDF or family photo to a different folder and open it.

Personal Cybersecurity

Common mistakes

The defaults that cost money, safety, or comfort

Trusting unnumbered dials

A fridge dial at "4" or water-heater mark at "A" is not a measurement. Instrument first, adjust second, recheck after the system stabilizes.

Using tire sidewall PSI

The sidewall is the tire's maximum cold inflation pressure under rated load. Your car's placard is the handling, braking, and load setting.

Warming the fridge to save pennies

Food loss and risk beat tiny compressor savings. Stay below 40°F and tune around 35-38°F.

Chasing 45% RH in a cold winter

Comfort humidity that condenses on windows can become wall moisture. In cold climates, the right number falls when outdoor temperature falls.

Replacing batteries, not alarms

Smoke and CO sensors age. Date labels matter more than a successful chirp test.

Installing the highest MERV filter sold

Filtration without airflow is bad HVAC. Use the highest rating your blower and filter rack can support.

Aggressive heat-pump setbacks

A big overnight drop can summon resistance heat in some systems. Watch aux-heat behavior and use smaller setbacks if needed.

Pre-rinsing every dish

Scrape solids. Let detergent and sensors do their job unless your machine or load type specifically requires intervention.

Doing the walk-through once

Settings drift, filters load, alarms expire, seasons change. Re-run this card every spring and fall.

Source map

Primary sources used for volatile numbers

Number family	Source	What it verifies
Water heater and scald	CPSC, CDC, DOE/Energy Saver	120°F scald recommendation, burn times, Legionella temperature control, energy-saving framing.
Food cold chain and cooking	FDA, USDA FSIS	40°F refrigerator ceiling, 0°F freezer target, safe internal cooking temperatures.
Humidity, filtration, radon	EPA	30-50% ideal humidity, below-60% mold guidance, MERV 13 caveat, 4 pCi/L radon action level.
Thermostat setback	DOE Energy Saver	7-10°F setback for 8 hours and up-to-10% annual heating/cooling savings.
Tires and TPMS	NHTSA TireWise and FMVSS 138	Use placard cold PSI; TPMS warning threshold around 25% below placard pressure.
Garage doors	CPSC	30-day inspection, 2x4 reverse test, photo-eye height guidance.
CO exposure	OSHA	50 ppm 8-hour occupational limit as context for why home alarms are not low-level monitors.

Seasonal tasks and service cadence around the settings on this page.