That burnt smell usually only happens the first time you turn the thermostat to heat for a electric heat pump or air conditioner at the beginning of the cold season. It’s due to built-up dust inside the air handler. Dust on the evaporator coils makes a minor burnt smell on that first heat start-up of the year. But when the electric heat strip is activated it’s more noticeable, because the surface of the heat strip gets much hotter than evaporator coils and it actually burns off the dust.

    The smell should be mild and fade away within an hour. But if it is persistant and strong, then it is caused by one of two reasons:

1) The air filter for the system is missing or damaged and has allowed excessive dust to build up inside the air handler, or 2) You have a heat pump system, which uses the circulating refrigerant to move heat to inside the home from outside. On very cold days in Florida, when the outside temperature drops below freezing, there is not enough heat outside to absorb and send into your home. So the system automatically switches to an electric resistance heat strip inside the air handler, essentially a larger version of the heating coils in a portable electric space heater. If you live in the part of Florida that rarely gets sub-freezing days, it may have been quite a while since the heat strip fired up, and there could be a dust coating built up over time—even with good air filtration. 

    So you should only be concerned about the burnt smell if it is unusually strong, long-lasting or recurring, or it’s an electrical-type of smell. Also, see our articles What does "AUX HEAT" and "EM HEAT" on my thermostat mean? and What is an electric heat lock out on a heat pump? and Why does the "AUX HEAT" (auxiliary heat) light keep coming on at my thermostat, even when it's not that cold outside? and When should I switch the thermostat to EMERGENCY HEAT for my heat pump air conditioner?

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  To learn more about heating and air conditioning systems, see these other blog posts:

• Frequently Asked Questions (FAQ) about Air Conditioning Troubleshooting

• Why is my air conditioner not cooling enough? 

• Why does my air conditioner keep shutting itself off?

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.