Wood burning fire pit on a wood deck protected by DeckProtect

Testing DeckProtect under a hot fire pit.

When is it safe to use a wood burning fire pit on a wood deck or on composite deck? We built a test deck so we could demonstrate what happens to wood and composite decking under different fire pits and under different conditions.

See how much damage a fire pit can do to a composite deck.

Ring of char left by wood burning fire pit on a composite deck
The Deck
Last year we were sent an image of a composite deck that had been scorched and melted by a fire pit. We asked what kind of fire pit had done this and we received the photo on the right. Would DeckProtect provide adequate protection? We knew it would but we decided to buy this fire pit and prove it. To be fair, the company that sells the fire pit tells customers not to use it on a deck unless you have an adequate heat shield under it. On their web site they recommend DeckProtect™.
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The Culprit
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This wood burning fire pit traps the heat underneath.

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Shown at left is the test fire pit on our test deck. Notice that instead of sitting on 3 or 4 legs, the fire bowl sits on a conical base. A base of this type has the effect of trapping the heat, which builds up and will therefore be a greater threat to the surface below. This fire pit is made in China from thin steel. There are a number of fire pits made in the U.S. from heavy forged steel that is much thicker. The trapped heat effect would be similar with the heavier fire pits.

The test deck is a 30" high framework that supports a 5 ft. x 5 ft. deck. The decking boards are not screwed down so they can be replaced when damaged.

To prove the effectiveness of DeckProtect we wanted to make sure that the fires we burned over DeckProtect were on hotter days and burned hotter longer than the fires we show damaging the decking boards.
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We cut an opening in the base of the fire pit to make a sort of oven door. This made a number of things possible, including answering the question of whether you can cook breakfast under a fire pit as well as over it. Notice the handle to the oven door. It is black plastic, which didn't last long, so subsequent photo sessions reveal a steel door handle.
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An egg cooked easily. Next we tried toasting a slice of bread and cooking a slice of turkey bacon. This process will take some practice since we left the pan in a little too long as you can see in this photo.
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Wood Decking was badly damaged.

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Above: After the first use of the fire pit shown above, the decking boards had blackened in the center, and there was a defined ring of damage that exactly corresponded to the base. This burn went strong for two hours, during which the "oven door" was removed several times (for our cooking experiments) allowing heat to escape.
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Above: After the second use of the same fire going strong for two hours, and the fire pit in the same position, the burn marks and blackening are more pronounced. During this test fire, we did not remove the "oven door" so there was no time for the heat to escape. It is not clear how much of a factor this was compared to the cumulative effect of using the fire pit a second time over the same boards.
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Click on this image to expand.
Above: a close-up photo from a different direction showing in detail the extent of the damage to the wood after the second use of the above fire pit without the protection of DeckProtect. It is important to point out that this particular type of fire pit with an enclosed base is bound to cause more damage than a fire pit with legs and some air flow beneath the bowl.
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Now with DeckProtect™ under the fire pit.

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Testing DeckProtect on Pressure Treated wood decking.
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Pressure Treated wood after the test.
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Testing DeckProtect on composite and PVC decking boards.
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Composite and PVC deck boards after the test.
The fires that burned the wood decking in the photos above burned strong for a little more than two hours in late afternoon and into early evening on a day with ambient temperature in the low seventies. If the fire to test DeckProtect were shorter, weaker and on a cooler day, we would not have the proof we need. Therefore we did the test in the middle of the afternoon on a day with ambient temperature around 80° Fahrenheit and fed the fire continuously to achieve a brisk burn lasting more than 3 hours.
We followed the same principle for testing DeckProtect with two man-made decking boards under the center of the fire pit. The light brown board on the left is Timbertech capped composite. The light gray board on the right is Fiberon PVC (no wood content).

With both tests there was no damage whatever to the Pressure Treated wood, the composite decking or the PVC decking. Because of the way the test deck is constructed, we were able to check the surface temperature of the decking during the burn. And there the temperature on the surface of the decking boards directly under the center of the DeckProtect ranged from 105° F. to 135° F. The surface temperature of the board 3" away from the DeckProtect were heated by radiant heat from under the fire bowl to temperatures as high as 175° F.
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Another Test
We wanted to demonstrate what a fire pit could do to samples of composite and PVC decking.
Read More
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