Modern Rumford MR 48 fireplaces Construction Guidelines For MR-48-1 Kit System
Cellar Building, Suite 300 1124 NW Couch Street Portland, OR 97209 Ph. 503-227-0547 Fax 503-227-0548 info@mobergfireplaces.com MODERN RUMFORD FIREPLACE CONSTRUCTION GUIDELINES FOR MR-48-1 KIT SYSTEMS 7/06/05 FOUNDATION It is essential that the support for the Modern Rumford be designed to carry the weight of this masonry fireplace. The support will typically consist of one of the following: a concrete block foundation over which has been cast a six-inch thick reinforced concrete slab, a thickened slab-on-grade concrete floor, or an engineered floor structure designed to carry this type of load. Make sure that the sub-hearth area is a completely non-combustible base, unless the structure is also engineered and approved for combustible underlayments. See attached installation drawings Typical Code Minimum Construction at the end of the Typical Construction Details section for general assembled dimensions with code-minimum thicknesses. Actual thicknesses will vary depending on individual design characteristics. Assembled dimensions with nominal 6 wide CMU construction are shown in drawings Typical Complete Kit Construction, found at the end of the Typical Assembly Drawings section. Consult with your engineer or architect to project actual weights to be considered for structural support design. FIREPLACE ASSEMBLY In first attached section, Typical Assembly Drawings, see color exploded isometric drawing KS-5 for typical layout of Modern Rumford System s components. Within that drawing, layout of Clean-Burning Kits Level One is similar for the MR 48-1 system. In addition, Assembly Figures 1 to 16 show a step-by-step process for the entire fireplace assembly. FIREBOX FRAME AND MASONRY CASING Place the base pan in position (Figure 1) to determine the exact placement of the fireplace. Draw an outline of the base pan on the supporting surface and do your masonry casing layout. Modern Rumford fireplaces can be constructed in a masonry casing with virtually any geometric footprint as long as code minimum wall thicknesses are maintained. Refer to Figures 3-7 for typical block layout in a corner installation. If reinforcing is coming up from below, make sure to align the vertical bars with the block cores. If you are installing Foamglas cellular glass insulation underlayment (to prevent heat migration downward and possible cracking of slab or heat transferring into engineered/approved combustible underlayment), cut the Foamglas to
fit under basepan and install into position on the prepared surface. Make sure that the surface is flat and level so that the unit will end up level and plumb. Bolt the rear wall frame to base pan (Figure 2) and install over Foamglas or into position on foundation slab. Set and level base pan on a layer of mortar (or thin-set if leveling over insulation) to assure future alignment of door-mounting frame and chimney breast above. Note the circular openings in the back and side walls of the frame for gas connections. Those connections should be installed before firebrick is set. If you are planning for a gas connection, consult Moberg Fireplaces and obtain a copy of instructions of Gas Connections for Modern Rumford Fireplaces. Cover the pan to keep miscellaneous debris from accumulating in it and potentially damaging insulation over air ducts. Once the frame is in place, lay out the first course of block or other all-masonry casing (Figure 3). Unpack the 2 rigid K-Fac mineral fiber board insulation, that comes standard with each kit, and cut in place to fit (Figure 4) vertically along side and rear walls of rear wall frame. Place first course in the slots around the back and sides of the basepan. Continue placing boards up against the backside of the frame until the firebox is insulated to the top (Figure 5). Do not use K-Fac as an underlayment for the basepan or other masonry. Continue construction of masonry casing until either 8 high block is built up seven courses or other masonry is built up to an equivalent point. Make sure that where the lintel bracket will sit is 56-5/8 high (measured from the bottom surface of the basepan) on each side wall, or flush with the top of the rear wall frame (Figure 6). If the walls are to be reinforced and/or poured with concrete, they should be poured during this phase (Figure 7). CHIMNEY BREAST ASSEMBLY It is now time to prepare the chimney breast. (Alternatively, the assembly can be installed after the firebrick firebox is built. See Figure 12.) The left or right pieces with the door frame-mounting plates pre-installed are the first chimney breast pieces that you are going to mount. Slide one 3-3/4 breast block onto the steel lintel tube, making sure that the mounting plate is to the outside of the 48 firebox opening. Continue placing the remaining four 12 wide refractory breast blocks, and then the last plate and 3-3/4 block. Make sure that the door frame-mounting plates are fully hammered on and are positioned correctly (left on the outside left, right on the outside right as you face the firebox opening). Blocks may be sealed with high-temperature or refractory sealant, but joints must be minimized (maximum 1/64 ) to insure a correct placement along the lintel. Use the door-mounting frame to check correct placement. The holes in the top of the doormounting frame should align with the stud bolts of the plates (and occur directly above companion holes on front face of base pan when installed). If the fireplace will have doors (vs. screens), set the door and recheck for plumb (front to back as well as left to right) and square. Remove frame and mount later. On the outside of the 3 3/4 refractory breast blocks, mount the support brackets that will rest on the adjacent masonry casing sidewalls. Attach the eyebolts into the support brackets and insert the 3/4 lifting pipe into the eyebolts. This creates a temporary handle with which to lift the entire chimney breast assembly into position. This will be a heavy assemblage, so make sure enough people are available to raise and lift it into place carefully, particularly if the mortar under the masonry you will rest the brackets on is not fully set. Or, you can raise and set the assemblage with a motorized or mechanical lift. Now bolt the door-mounting frame to the basepan at the bottom and to the breast block/door frame mountingplates at the top. Check the door-mounting frame for plumb, level and square. Adjust the chimney breast placement if the frame is way out of alignment, and/or shim the frame with washers at mounting points if minor adjustment is all that is necessary. Once the breast is in place, and you have checked the (plumb and level) door-mounting frame for alignment, remove the pipe and eyebolts. FIREBOX CONSTRUCTION Now it is time to go back and build your firebrick firebox. Note: you do not have to do it in this order; you can build the firebrick firebox before you mount the chimney breast, but you must leave room for the chimney breast to fit in and confirm the fit before you build the firebox. Lay 1-1/2 Foamglas in the open cavities of the basepan to bring the base for the firebox hearth up to the level of the top of the inner air channels (or lay firebrick splits if insulated protection is not required for the sub-hearth base). Then, lay firebrick splits (Figure 8) for the firebox floor (inner hearth) and under the
area that will form the back and sidewalls. Now, you can lay the full-size bricks that form the back and side walls (Figure 9). Modern Rumford fireboxes can be built either with firebrick laid flat, normally at 4 to 4-1/2 thick, or on edge. If laid on edge, make sure that walls are at least 2 thick and that when combined with the casing masonry, they satisfy the minimum requirements of the local code, as well as the architectural requirements of the project. Follow the angles set up by the back frame, cutting the firebrick to overlap and/or fill the corners. Because the back wall is on an 8-1/2º slope, firebrick must be tipped forward from the very first course. Since the rear wall will be laid on an angle and the sidewalls laid level, they won t bond through. Typically, the rear wall should run behind the sidewalls. However, when sawn-face firebricks are used (soapstone for example), they can have the 8-1/2º slope built into the face and can be laid level and also can be bonded through. Build the firebox up to the top of the rear wall frame on the back wall and on the side walls (Figure 10). You will need to cut the brick around the breast blocks (Figure 11), or if you decide to install the firebox before the chimney breast, wait and do the last few courses with breast blocks in place. Make sure at the top of the back wall you have at least 5 between the back wall and the top of the breast blocks for the throat of this fireplace (Figure 12). SMOKE CHAMBER AND DAMPER CONSTRUCTION Lift the large metal smoke chamber liner into position and align the 1 flange just behind the breast block ledge. This is also a heavy component, so make sure enough people are available to lift into place, or a mechanical lift is available. The front face of the smoke chamber should line up with the interior edge of the breast block (Figure 13), and the front flange should rest on the breast block assembly. The rear flange should rest on the masonry casing/rear wall of the fireplace. Cut the K-Fac insulation to fit the outer side and back surfaces only of the smoke chamber and adhere it to the metal surface with high-temperature silicone or refractory cement. The front face should already have a thin ceramic fiber blanket pre-installed. Then, build a solid masonry casing around the metal smoke chamber, also setting on the casing around the firebox, until you reach within 3/8 of the top of the smoke chamber. This casing should be constructed similar to the casing built below, using CMU, brick masonry or concrete masonry, as allowed by code, and in the thickness necessary for both code and minimum structural requirements. For example, if an all-masonry chimney will be placed above the smoke chamber, the casing must be corbelled, reinforced with angle iron, or otherwise built to transfer the weight to the firebox casing below. Consult your architect or engineer for the design of structural masonry casings. The smoke chamber casing must also rise adjacent to the insulation and corbel or taper so that it will physically support the flat frame plate of the damper assembly, at least at the front and back edges of the plate. At this point you are level with the top of the smoke chamber. If reinforcing is required, you should then do your final concrete pour to reinforce your block work and prepare for supporting the chimney. Make sure that neither masonry casing nor concrete pour rise above the level of the metal smoke chamber, and create a flat and level surface for supporting the heavy frame of the damper assembly. Also, ensure that all insulation is encased in masonry and/or covered with mortar or concrete (at least 3/8 thick), or will be covered by damper frame plate. Then install the chimney damper and frame plate assembly (Figure 14). This assembly must be lowered into the smoke chamber so that the guide pin (at the rear of the circular ring which supports the damper blade) slides down the slot at the rear of the smoke chamber. Make sure the assembly goes down until the flat frame of the damper assembly rests both on the metal smoke chamber itself, and on the masonry casing. Four holes in the frame can be used to lag-bolt the assembly into the masonry, if desired, for securing the assembly in position. Make sure that the stainless damper cable is hanging down into the smoke chamber, and is accessible for connecting to stop bracket and handle later on (see damper handle and grating). CHIMNEY AND OUTSIDE AIR The MR-48 systems require 14 round (I.D.) UL-listed, insulated metal flues, or masonry flue liners that are typically slightly larger. If you are going to construct the chimney in masonry, you should then set your first 16 x 16 square (O.D.) flue liner (minimum 14 x 14 I.D.) or 15 round (I.D.) flue liner and continue with your masonry chimney. Or, if you are going to install a UL-listed insulated metal chimney, then you should set and secure your factory-built anchor plate which makes the transition from the smoke chamber to the metal chimney system. Follow the chimney manufacturer s instructions for mounting the plate and ensure that no portion of the anchor plate or chimney system interferes with damper blade before proceeding further. Then proceed with the assembly of your chimney. We recommend a minimum of 15 feet of actual flue for good operations.
At the rear of the fireplace, there is a 3 x 9 inlet that connects to the air channels inside the base pan. From this opening, connect a minimum 6 round or 4 square transfer duct to an exterior screened intake located at or below firebox level. You can utilize the optional outside air adapter available from Moberg Fireplaces, which allows for optional connections in four directions, or you can customize a non-combustible connection, using metal or masonry transfer ducting which meets the minimum requirements of the local code. Make sure the intake screening does not restrict the opening to less than 16 in. 2 net free area. If the total length of the intake connection will exceed 15 feet and/or require more than two 90º offsets, it may be necessary to increase the size of the transfer ducting, to assure proper minimum air flow. Consult your architect or engineer for the design of circuitous intake ducts and/or contact Moberg Fireplaces for more information. To prevent the unwanted infiltration of cold outside air, you can install a damper in-line of the transfer duct and/or purchase the optional air outlet cover from Moberg Fireplaces. Not all installations will require outside air connections for meeting minimum code requirements, but the connection of the outside air duct is important for assuring the clean-burning and smoke-free operation of Modern Rumfords in most applications. However, the location of the intake at the exterior of the fireplace must not be placed where it could ingest flammable gases or liquids, or conversely where propane from a loglighter or gas log set could expel gas into a flammable environment, or in exterior locations that are subjected to negative pressures during adverse wind conditions. MAKE-UP AIR PROVISIONING In planning for the installation of a Modern Rumford, as with all open fireplaces, it is necessary to provide make-up air for combustion and proper operation. This is an addition to combustion air, as it represents unrestricted air that must cross the opening and be exhausted up the flue. Although make-up air is effectively a necessary heat loss in all open fireplaces, the MR 48 operates without spillage utilizing less room air than most open fireplaces. For wood burning applications, we recommend providing make-up air through the building s mechanical air handling system adequate to allow up to 500 cfm for fireplace opening, with the following exceptions: For fireplace installations using 6 round outside combustion air system built into the hearth, makeup air can be reduced by 20%, to 400 cfm. For fireplace installation with gas log sets having outputs less than 100,000 BTU/hr, makeup air can be reduced by 50%, to 250 cfm. However, mechanical system capacity must be sized for larger volumes, if future wood burning operations are possible. In the room containing the fireplace, make-up air must either be 1) continuously supplied by an air-handling system, specifically for the fireplace, or 2) be available through activation of a switch or other control mechanism before the fireplace is operated. If make-up air is also a proposed substitute for code-required combustion air ducting, the use of this air supply must be coordinated with all fireplace operations, and be acceptable to the jurisdiction having authority as providing an equivalent standard. We recommend that the mechanical contractor furnish all hardware and size the installation components properly prior to fabrication and installation of the mechanical air handling system in the room containing the fireplace. Due to the possibility of a power failure during fireplace operations, it is necessary to ensure the optional availability of make-up air in the room containing the fireplace, from openable windows and/or doors of equivalent cross-sectional area as the fireplace opening. FINISHED FACING Now the fireplace is ready for its finished facing. Detail as in architects or designers plans and per minimum code requirements. See attached section Typical Installation Details for samples of finished solutions. The Modern Rumford does not provide any limitations to finish design beyond the minimum dimensional specifications shown here, or the specific internal geometries defined by the kit construction. If doors or screens are going to be mounted to the doormounting frame, be sure that finished facing/surround does not impinge on the minimum 48 wide and 40 high opening created by the door-mounting frame.
DAMPER HANDLE Clean-Burning Level One Modern Rumford Kits utilize the unique Moberg Fireplace Single-Stage Dampering Mechanisms. (Standard manual cable-activated or optional motorized actuators are available). Before they can be properly operated, the standard stainless damper cable and handle assembly and the stop bracket must be installed and fitted. Unless they are factory pre-installed, follow these instructions for assembly: Attach stop bracket to threaded studs found on right hand base of smoke chamber with key-hole end down, and bolt into place with stop bracket keyhole flange toward the inside of the smoke chamber. (See Single-Stage Damper Operations illustration at the end of assembly figures). Pull hanging cable down from the damper blade through the throat of firebox and then pull the separate cable end of the handle assembly up through keyhole in the stop bracket. Pull down on the damper cable until damper blade hits the stopping flange and is in closed position. Attach the handle assembly cable to the damper cable by threading the damper cable into the lock-joint connector, then pull up on the handle assembly cable until the lock-joint connector is in position just below the keyhole flange. Tighten the lock-joint connector so assembly can be tested for open and closed position. Adjust, if necessary, for easy release. The damper is manipulated by pulling the cable and stop connector out of the keyhole slot and letting the counterweight action of the damper release the cable up (open) or by pulling down to align the cable and stop connector in the closed position. See Modern Rumford Level One Fireplace Operating Instructions for further details. NOTICE The Modern Rumford Fireplace Kit is a guidance system for constructing a clean-burning, code-compliant all-masonry fireplace. As a masonry fireplace, it must adhere to local fireplace code. THIS KIT DOES NOT IN ANY WAY REPLACE THE MINIMUM CODE REQUIREMENTS FOR MASONRY FIREPLACES. It is the intention of the manufacturer that the Modern Rumford Level 1 Kit be installed and assembled according to the following Construction Guidelines, as well. All aspects, including finishing treatments and clearances to combustibles, chimneys, etc., must also conform to local codes for standard masonry fireplaces. If you have any questions or doubts about what is allowable in your area, consult your local building code requirements for masonry fireplaces before proceeding with the installation of your Modern Rumford Kit.
Modern Rumford MR 48 fireplaces TYPICAL ASSEMBLY DRAWINGS
Modern Rumford MR 48 fireplaces PHOTOS OF TYPICAL ASSEMBLY
Concrete supports at floor level plus courses for raised hearth. Mortar bed to set basepan (shown at rear). Basepan set and leveled.
Attaching backwall form frame Backwall attached and ready for firebrick.
Air intake adapter shown at rear. Gas line attached.
4 block at rear for shallow installation. Board insulation applied to rear and sidewall.
Block surround to 3 rd course. Block to course 7 (56 5/8 )
Insulation and block to top of firebox (course 7). Shoulder bracket, lifting eye, breast block, lintel bar and refractory mortar. Breast block and lintel bar ready to be lifted into place.
Breast block assembly being set into place. Attaching Door frame.
Breast block assembly in place with lifting rod still in place. Door open frame attached. Smoke shelf.
Smoke chamber in place. Masonry surround for the smokechamber.
Setting damper on smoke fireplace capping slab. Finished blockwork ready for firebrick, veneer and chimney.
Modern Rumford MR 48 fireplaces Typical Construction Details