By Tony — the guy who’s been called out at 5 a.m. more times than he can count because “the heater won’t light in the cold.”

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🛠️ Introduction: The Cold-Weather Lie Most Homeowners Believe

Every winter, people blame the heater:

• “My propane heater won’t fire when it’s really cold.”

• “Ignition is slow below 20°F.”

• “The flame sputters on cold mornings.”

• “It runs fine all summer — what’s different now?”

What’s different?

Your system design doesn’t work in freezing conditions.

Propane heaters — Reznor, Modine, Hot Dawg, Sterling, Rinnai — ALL can start reliably in sub-zero weather IF the system supplying them is designed correctly.

Cold doesn’t break heaters.

Cold exposes design mistakes.

This article explains exactly why propane heaters fail during cold starts and how Tony designs systems that light perfectly even at −10°F.

Reznor UDX 60,000 BTU Propane Unit Heater

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🧊 1. Propane Pressure Drops Hard in the Cold — And Most People Don’t Design for It

Propane pressure is a function of temperature.
That means:

• As temperature drops, tank pressure drops.

• As pressure drops, gas flow drops.

• As flow drops, the heater can’t ignite cleanly.

Here’s the real chart homeowners never see (approx values):

If you design a propane system based on summer pressure, it WILL fail in winter.

Tony Rule:

design gas supply based on the coldest possible temperature your region hits — not the warmest.

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🪫 2. Small Tanks Freeze Faster — And Starve Heaters

Most cold-start failures happen on:

• 20 lb tanks

• 30 lb tanks

• 40 lb tanks

• Undersized outdoor cylinders

Why?

Because propane evaporates slower when cold, and smaller tanks can’t keep up with the heater’s BTU load.

Example:

A typical 60,000 BTU heater needs at least:

• a 100 lb cylinder
  OR

• two 40 lb cylinders manifolded
  OR

• a buried/above-ground household propane tank

A single 20 or 30 lb cylinder WILL frost over at < 25°F.

Frost = no vapor pressure = no ignition.

Tony Rule:

Never run a garage heater off a grill tank in winter.
Ever.

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🧯 3. Regulators Fail in the Cold More Often Than Heaters Do

Regulators hate cold for two reasons:

1. They ice internally

2. Their diaphragm stiffens

Both of these cause:

• delayed gas delivery

• reduced flow

• lower pressure

• inconsistent ignition

• flame dropout

And if snow or freezing rain hits the regulator vent?
That’s a total shutdown.

The heater is fine — the regulator is frozen.

Tony Fix:

✔️ use cold-rated regulators
✔️ install regulator hood
✔️ mount above snow line
✔️ keep vent pointed down
✔️ ensure vent screen is clean
✔️ use two-stage regulation for long runs

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🌬️ 4. The “No Combustion Air” Problem — Weather Stripping Makes It Worse

Modern garages are airtight:

• insulated doors

• sealed bottom gaskets

• spray-foam walls

• vinyl windows

• airtight overhead doors

Good for energy.
Bad for propane heaters.

When the burner attempts to ignite, it needs oxygen.

Cold starts fail when:

• the room is airtight

• the heater starves for combustion air

• cold dense air pushes exhaust back into intake

• vent termination is snow-blocked

Tony Rule:

A tight garage = sealed combustion or a dedicated combustion air intake.

Otherwise your heater suffocates in the cold.

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🧊➡️🔥 5. Cold Metal Delays Draft — So Ignition Fails

On natural-draft or power-vent heaters, the chimney must establish draft.
In freezing weather:

• vent pipe is ice-cold

• warm exhaust hits cold metal

• condensation freezes internally

• draft is delayed

Result?

• ignitor fires

• gas valve opens

• flame partially lights

• rollout or pressure sensors trip

Homeowners think “bad ignitor” — but it’s a draft problem.

Tony Fix:

✔️ increase upward vent pitch
✔️ add cold-weather termination hood
✔️ keep intake/exhaust separated (Tony’s 2-Vent Rule)
✔️ extend vent beyond snow eddies

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💨 6. Backdrafting Destroys Cold Ignition

Cold, dense outside air is heavier than warm air.
If the vent termination faces the wrong direction, cold air pours back in.

This causes:

• no ignition

• flame lift

• spurting/sputtering

• rumbling ignition

• flame rollout

• condensation inside burner area

Backdrafting is ALWAYS a design flaw.

Tony Rule:

Never terminate intake/exhaust on the windward side of a garage.

Rotate 90° or extend the vent as needed.

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🔄 7. Why Cold Starts Go Bad Fast (Tony’s Breakdown)

On a warm day, systems get away with bad design.

On cold days, margin disappears.

Here’s the chain reaction:

1. Tank pressure drops

2. Regulator output drops

3. Gas flow slows

4. Ignition gets weak

5. Draft is delayed

6. Combustion mixes poorly

7. Backdrafting increases

8. Condensation forms

9. Burners foul

10. Heater enters retry/lockout

Every single piece is connected — and every step is a design flaw.

Not a heater flaw.

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🧰 8. Tony’s Cold-Start Checklist (Fix Before Winter)

Here’s exactly how Tony makes heaters fire reliably at −10°F:

✔️ 1. Oversize the tank

100 lb minimum
250–500 gallon household preferred

✔️ 2. Use two-stage regulation

Tank → first-stage → building → second-stage → heater

✔️ 3. Use cold-rated regulators

NFPA-approved, low-temperature certified

✔️ 4. Keep regulator above snow line

Minimum 12–24 inches

✔️ 5. Install sealed combustion (direct-vent) when possible

Cold garages require it

✔️ 6. Add 2-inch clearance under snow guard above vent

Prevents snow drift blockage

✔️ 7. Follow Tony’s 2-Vent Rule

Intake and exhaust must be separated
Backdrafting kills cold starts

✔️ 8. Pitch exhaust upward

1/4 inch per foot minimum

✔️ 9. Avoid flex vent pipe

It traps condensation instantly

✔️ 10. Keep heater angled correctly (15–20° down)

Improves air mixing and combustion reliability

✔️ 11. Verify gas pressure using a manometer

Static and dynamic readings

✔️ 12. Install a garage mixing fan

Prevents stratification and helps draft stabilise

✔️ 13. Don’t run heater off a grill cylinder

It will fail below freezing every time

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🔥 9. The 3 Cold-Start Myths Tony Hears Every Winter

❌ Myth 1: “I need a bigger heater.”

No — you need a bigger tank, better venting, or correct regulator.

❌ Myth 2: “My ignitor is bad.”

Ignitors rarely fail.
Ignition fails because gas flow or draft is wrong.

❌ Myth 3: “Propane doesn’t work in extreme cold.”

Propane works down to −40°F if designed right.

These myths cost homeowners thousands in unnecessary repairs.

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📘 10. Verified External Sources 

These sources confirm everything Tony teaches about propane and cold-weather operation:

1. ASHRAE Air Distribution Fundamentals
   

2. Modine Hot Dawg Installation Manual (Mounting & Throw Charts)
   https://modinehvac.com/

3. Reznor UDX Engineering Specifications
   https://www.reznorhvac.com

4. Energy.gov – Heat Distribution & Stratification Control
   

5. Building Science Corporation – Air Mixing & Comfort Control
   https://buildingscience.com

6. HVAC Ventilation & Throw Distance Principles (Titus HVAC)
   https://www.titus-hvac.com/

These are gold-standard references used in HVAC engineering.

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🚀 Conclusion: Cold Starts Are NEVER Heater Problems — They Are System Design Problems

If your heater:

• sputters in the cold

• fails to ignite

• struggles to stay lit

• lights only after several tries

• locks out on cold mornings

Your heater is NOT the enemy.

Your system design is.

Fix the design and the heater becomes unstoppable in ANY weather:

✔️ reliable ignition
✔️ stable flame
✔️ lower propane usage
✔️ longer equipment life
✔️ zero cold-start failures

Cold doesn’t beat heaters.
Bad design does.

And now you know how Tony designs systems that fire perfectly — even in brutal winter conditions.

Buy this on Amazon at: https://amzn.to/4oCrGcV

In the next topic we will know more about: The Propane Pressure Puzzle — Why Your Heater Isn’t the Problem, Your System Design Is