Test the seal on the loading door with a strip of paper. Open the door on a cold heater, place the paper across the gasketed area of the door, then close and latch the door. Try to remove the paper by pulling. The paper should not pull out easily. If there is an area where the paper slips out easily the door seal needs attention. The first thing to try is to adjust the door latch. Some heaters have a mechanism to adjust the door as the gaskets compact through use, and some do not. (That is something to look for when purchasing a new wood heater.) If you can’t adjust the door, or if after adjustment the paper pulls out easily in one or more places, you will probably have to replace the door gasket(s).
All air-controlled appliances have a method of reducing random leaks into the firebox so that air only enters the heater through the air control. While a very few older heaters have carefully fitted ground cast iron surfaces that seal reasonably well without gaskets, virtually all modern wood heaters use gasket material around the loading doors to seal them. Some ash pan doors also have gaskets. Gasket material has evolved through the years from asbestos rope to fiberglass ropes in various sizes and density. The usual gaskets are 12 – 25mm thick. If in doubt about what size and density to use, remove the door and bring it into our factory to test a variety of ropes in the groove. You can purchase gasket cement in a small tube or tub. If you can’t find gasket cement don’t despair. You can use common silicone sealant in a caulking tube. High temperature silicone is not necessary because the temperature rating of household grade seems to work well enough.
To install the gasket, remove the door and place it on cardboard or cloth to prevent scratching of the finish. Pull out the existing gasket; on some heaters you’ll have to disassemble the door to get the gasket out. Clean the gasket groove with an old screwdriver to remove any lumps of old cement. Clean the groove thoroughly with course steel wool so that it provides a good clean surface for the cement to stick to. Using the cement or silicone, apply a narrow (usually 6 – 12mm wide, depending on gasket size) bead along the entire groove. Lay the gasket in the groove without stretching or bunching it, starting half way along the hinge side. Cut the gasket slightly long so that the ends slightly bunch into each other forming a good seal. Press the gasket into the cement. Mount the door and test the seal. Slamming the door lightly, you should hear the muffled sound of the gasket, not metal, hitting the heater body. Test the seal with with a piece of paper.