Ash pits safety, clean out doors, ash dump doors
Question: There was a black metal plate in the rear of my fireplace and it fell into a cavity below the freplace foor/hearth. What is the purpose of this cavity? What will happen if live embers fall into the cavity? There is no opening in the basement to access the cavity. How can I access it and remove the ashes I see down there?
Response: The metal plate you describe sounds like an ash dump door. Some are simple metal plates, but most have a hinge mechanism to open and close a metal flap of sorts surrounded by a frame. There are a few different sizes and the older ones may not be the same size as the newer ones, If you can’t retrieve yours, you may need to enlarge or reduce the hole size in the fireplace floor to make a new one fit. A 1/4″ steel plate a couple inches larger than the hole can also be used to simply cover the hole. Metal tabs or screws should be welded or bolted onto the underside to keep the plate from inadvertently shifting away from the hole. Many people just set a very large plate over the hole and are careful not to move the plate. The larger the the plate the less likely it will shift far enough to allow embers to fall through the hole.
The cavity, or ash pit, is used as an ash collection area. Ashes can be swept into it with minimal dust entry into the room. Usually there is a ash pit clean out door located below the fireplace, near the basement floor. Houses without basements, having chimneys on an exterior wall, often have a clean out door just above ground level on the exterior wall of the chimney.
Removing ashes from the clean out should be done periodically, though many people neglect doing so for several years. The concept is that ash removal and consequent dust creation is preferable in a basement (particularly an unfinished basement) or outside. Since ash pits are usually a very large, ash removal can be done less often than ash removal directly from a fireplace.
Important: Ashes and coals and embers should not be allowed to enter the ash pit until they are completely out and no sparks or any other form of combustion is taking place. As a greatly experienced wood burner who has seen ashes (that appeared dead) burn vacuums, brushes, carpets, wood floors, 5 gallon buckets and human flesh-mine. I strongly recommend waiting at least 72 hours after your fire goes out before assuming there are no live ashes. Even then, you must either sweep the ashes into your ash pit or place them in a double bottomed metal ash bucket, not a single bottom coal hod or 5 gallon bucket - and then securely place a lid on the bucket and place the bucket outside several feet away from your home and out of direct wind where the lid might blow off or the bucket might fall or blow over. No garages or car ports or gas mowers etc nearby, either! Seriously, improperly storing ashes starts many a house fire.
Do not use your ash pit until you do clean it out and asses it’s suitability for use. Though you may never know exactly how it is constructed, you can make certain determinations to assist you in deciding whether or not to use it. Place a powerful light inside the ash pit and use a hand held mirror to see if there are any combustibles present anywhere inside the ash pit. Carefully inspect all six inner walls, top, bottom, left, right, front and rear. If combustibles are present, they must be removed. If wood framing is found, a chimney expert should be consulted to determine how to remove it and whether or not masonry or steel supports will be needed as a re-support. Sometimes wood is used as a form to aid in the placement of brick or concrete and once the wood form is removed occasionally no re-supporting is required.
Since you presently have no clean out door, you have to choose whether or not to to put one in. Many people choose not to use their ash pit, particularly if the basement is finished, as the benefits of not making dust in a finished area are nonexistent. If the basement wall directly under the fireplace is unfinished, with no combustibles on it or in it, it will be fairly simple to install a new clean out door. ”Lock Top Corporation” has a great cast aluminum, rust proof, insulated door with a high temperature gasket. It’s the best I’ve seen. 8″x8″ doors are common, though an 8″x12″ door makes ash removal much easier. (By the way, if you ever use a vacuum for ash removal, wait 4 or 5 days after you think your fire is out.) Feeling for heat is very unreliable. The suction and resulting wind will turn a single spark into a burning vacuum in a second or two.)
Installing a clean out door is best done with a grinder or circular saw utilizing a diamond or carbide masonry blade. Diamond blades are much faster and given the huge amount of masonry dust created, speed is of the essence. If the chimney base is brick, a heavy duty chipping hammer can be used; less dust, but a less accurately cut hole. Hollow block are very delicate and if you use a chipping hammer you may need to lay a few brick to fill in areas where more masonry than intended is removed. (Chipping and demolition hammers are rent-able at $35 to $45 dollars a day)
Before cutting a hole into the ash pit, tape and drape plastic from floor to ceiling all the way creating a 5 or 6 foot perimeter dust barrier around of the base of the chimney in the basement. Make this tent like enclosure as air tight as humanly possible. If the ceiling and walls are finished, tape plastic over them-inside the plastic tent you have created. Either tape the plastic to the floor or place lumber or other flat weights all the way around the base of the ”tent.” Next, if available, place a shop vac with a good filter inside the tented area and use it to catch most of the dust as it exits the cutting tool you use. Wear gloves, goggles, a silica dust approved mask and ear plugs. You may want to wear a disposable dust suit and hood as well.
Look down the ash dump hole in the bottom of the fireplace and see how the shape of the ash pit corresponds to the hole. It may be centered or more to one side than the other. Make note of this. In the basement you should be able to visually determine where the chimney base is located. If not, use a tape measure and measure the fireplace chimney’s distance to exterior walls on the floor level where the fireplace is located and then use these measurements to calculate where the chimney is in the basement. It will generally be the same distance from the basement walls as it was from the level above. Compensate for any framing, trim or other items that may effect your measurements. Now you should be able to determine the approximate center of the ash pit. Clean out doors are usually located a few inches above the floor and close to the center, left to right, of the ash pit. If the chimney base’s walls are covered with combustibles, you will need to remove the combustibles from the area where the door is to be placed. Then the clean out door can be placed directly on the masonry. An access panel or door can then be placed on the finished surface.
Beware that ash pits walls that are covered with combustibles such as drywall and framing are susceptible to causing house fires. All ashes in the fireplace and the ash pit should be considered flammable because they contain some unburned material. Be sure all of you ashes are out and then wait an extra few days to make sure before placing them into the ash pit with extra precaution if the pit wall(s) have been covered with a combustible material. Cleaning out your ash pit frequently, reduces risks by reducing the amount of potential fuel inside the pit.
Once you’ve located the pit, make a small hole, through the chimney wall and into the ash pit, near the floor and near center of the pit from side to side. The masonry will usually be 8″ thick. The door does not necessarily need to be located in the center of the pit, though the closer to center, the easier the ash removal process.Use this small hole to judge where you have entered the pit. Make any adjustments to the entry location and proceed to enlarge the hole accordingly. The door should come with instructions, but basically you need to make the hole as square or rectangular as possible and the size recommended by the door manufacturer. The lock top has set screws that press outward, toward the sides of the hole you have made, to hold the door in place while the adhesive recommended (silicone caulk) dries. Cast iron, crude and not very airtight doors should never be used behind finished wall access panels as they leak and are not insulated. If the basement is not going to be finished a cast iron door may be used, but keep combustibles a 3′ away from the door. Better yet, just get a Lock Top clean out door. They are insulated and fairly air tight.
Grinders and carbide blades cut pretty accurate holes, but a little chipping with a hammer and chisel will be necessary to cut the corners and to achieve the full depth, since saws and grinders only reach a couple of inches. However, only the first inch or so needs to have a clean edge for the Lock Top set screws to grab onto. If you use a cast iron clean door which will generally not have set screws or if you use the Lock Top clean out door and the set screws don’t hold well, set the door in place with a liberal amount of pure silicone caulk between perimeter of the door frame and the perimeter of your clean out hole. Push the door firmly, squeezing the caulk between both surfaces and then place a heavy object against he door to hold it in place until the caulk is firmly set.(12 to 16 hours or so) Any gaps or irregularities around or inside the door can be filled in with mortar mix or similar cement. If the cement sags or falls down, dampen the wall, make the cement drier and try again. If it still falls, try building up the cement in layers. Very heavily bodied and sticky cements are available at specialty stores as well. Insulating cement, Chamber tech 2000, stove cement, fireplace cement and pure Portland cement all have some of these qualities.
Good luck and thanks for the inquiry. I never thought to address this topic and it is a very important one.
Dave Myers
