When you buy a fireplace, one of the last things you may expect is to have cold spots around the unit. Though really strong stoves can put off enough heat to cover more than 2,500 sq. ft., they aren't contributing anything when they are not burning and it's important to prevent the opposite problem of cold air intrusion when this is the case. In this article, we will discuss the reasons why you may get cold areas around your stove or fireplace and what you can do to resolve that.
Most factory-built fireplaces have a heat exchanger that surrounds the metal combustion chamber. When a fireplace is burning, heat flows through the metal combustion chamber into the heat exchanger. That heats the air in the heat exchanger and then that air rises and comes out of the top of the fireplace as convective heat.
The problem comes when, open dampers, poor insulation, and or negative pressure in vent pipes cause the reversal of that process. When a heat exchanger is exposed to very cold air, that air then cools the overall temp of the exchanger and the air drops to the bottom of the firebox and escapes the bottom of the unit. And you end up with cool air around the base of your fireplace. With wood-burning units, when they are not in use, you need to keep the damper closed to ensure cold air doesn't flow into the firebox. If you have a gas log system over a wood burning fireplace, your damper will need to stay partially open, so keep that in mind.
Poor insulation affects gas and wood fireplaces alike. Unfortunately, all types of chimneys have issues with negative pressure since chimney chases are not airtight. In that case, you would need to replace whatever is allowing that to happen. If you have a direct vent gas fireplace, check to see if the glass is getting cold while it is not running. Normally, the pilot light should stay lit to prevent this. If the glass is cool & cold air is coming from the bottom of the fireplace, then you may have a poor insulation or negative pressure issue.
If you have a wood fireplace & are keeping the damper closed, its probably poor insulation or negative pressure allowing the cold air to come in. Hiring a chimney sweep is a good place to start for a wood burning fireplace. They will do a thorough inspection & be able to tell you what is going on. To resolve an issue with negative pressure, you will need to look for places air is being sucked out of your home. Electric fans and attics are common culprits for this kind of thing. Poor attic insulation causes a ton of problems and that can't be solved by stopping up the bottom of a fireplace to prevent airflow.
One interesting way to try to find negative pressure in your house is to weigh a helium balloon and see where it gravitates to. It will take some time for it to move towards the source, so you need to let it float while you are asleep or not in the home to make sure your presence doesn't disturb the flow of air. When you find the source of negative air pressure, address that problem and your cold fireplace issue will be resolved.
After reading this article, you should have a better understanding of the ins and outs of fireplace heating and why you may find cold air around your unit. Should you have more questions, please give our NFI-certified techs a call at 800.203.1642. You can also review our library of articles here.