First, understand that EIFS is combustible and can catch on fire if it gets hot enough. Wood studs, wood sheathing and many common types of siding are also combustible. Obviously, this heat needs to be kept away from the EIFS. With EIFS that uses EPS as the foam insulation, the melting point of the EPS is low enough that even though it may not burn, it might melt and flow, ruining the EIFS. The point is to make sure that the type of fireplace and flue is suitable for use in proximity to EIFS. The problem usually isn't the firebox or the chimney flue, as these are rated so that they can be used within a wood framed enclosure with minimal clearances between the flue/firebox, and the wood framing/sheathing. However, at the top of the chimney, a different issue surfaces.
Looks good, tastes badOften, the top of an EIFS-clad chimney is capped with EIFS, with a low slope. Even though this may look nice, it's a bad idea. For one thing, the EIFS will not last very long in such an exposed, low slope position-water gets to the EIFS lamina, substantially reducing its life. Also, sparks coming out the chimney might land on the EIFS, potentially causing a fire. At very least, soot would accumulate on the low slope surface. When it rains, the soot is transported of the low slope surface and onto the vertical surfaces of the EIFS-clad chimney enclosure, making ugly stains. The right way to do the top of the chimney is with a large sheet metal flashing that covers the entire low slope surface and that turns and overlaps onto the vertical side of the chimney. This issue of soot, or other combustion byproducts, is especially a problem with airtight wood stoves, which tend to create more of a greasy, creosote-like residue that is really difficult to remove from EIFS.
Speaking of chimney tops, sometimes there are lightning rods on the tops of chimneys. Oftentimes, there are lightning rods on the tops of EIFS walls, too. There's a temptation to bury the lightning conductors (those heavy wires) in the EIFS foam layer by notching out the foam. Surely, this would look better but if there is a strike, these wires can get hot as hell, and could melt the foam or set it on fire. Instead, mount the wires on the outside of the EIFS, preferably using insulated standoffs.
Some chimneys go right through the middle of a roof large area, such as when the fireplace is located in the center of the building at the roof peak, as on a traditional Cape Cod-style house. In this case, the chimney is surrounded on all sides by roofing that slopes away from the chimney; water does not tend to flow toward the chimney. More commonly, the chimney is on the side of the house. This means that the EIFS on the chimney may come down and terminate at the edge of the roof. This condition requires a couple of special details.
A kickout flashing is needed on the down-slope sides of the chimney where the roof slopes down past the EIFS and where the EIFS continues below the roof edge. This is needed to keep water from getting back behind the EIFS. Prefabricated molded plastic kickout flashings are available that are properly shaped and which save the hassle of fabricating one from sheet metal.
Also, if the roofing slopes down and meets the side of the chimney of the "up slope," a cricket flashing is needed at this point to divert the water around the sides of the chimney, rather than having it back up against the chimney. This large flashing is a bit pricey to fabricate and install but keeps water from getting up under the bottom edge of the EIFS.
I've seen cases where the designer wanted to continue the substantial EIFS-chimney look into the interior of the house by using the EIFS indoors. The codes do no permit using EIFS indoors but you can get the same look by applying EIFS finish coatings onto drywall.
Foam stoneOn chimneys that are clad with EIFS, it is not uncommon to use foam shapes to mimic the look of stone. This can make the chimney look "substantial" and "nice" and "expensive." If this is your aim, the foam shapes should be made of the same EIFS product that the rest of the EIFS uses. Mixing different types of foam shapes, especially those that use basecoat materials and foam insulation types that are different than the main EIFS walls, tends to result in cracking and adhesion problems; don't try to put a Chevy engine in a new Ford and expect to get warranty coverage from either dealer.
Your chimney might happen to be one of those old fashioned, uninsulated, metal stove-pipe-type contraptions. If such a chimney pipe goes directly out through the roof, then that type of pipe is not an EIFS issue. But if it goes out through a sidewall and then turns and heads up vertically, make sure the pipe is far enough away from the EIFS so the heat does not bother the EIFS.
Often, the fireplace is located on the ground floor on a sidewall. This means that sometimes the chimney enclosure may be in a part of a wall that extends out past the main wall. Like other nearby EIFS areas, make sure the bottom edge of the EIFS is far enough above grade that it isn't affected by ice and termites. The codes often specify minimum clearances, usually at least 4 inches but sometimes 6 or 8 inches. If the EIFS on the chimney comes down and butts into a hard surface, such as a concrete walkway, water can get under the edge during winter. If ice gets below the EIFS and freezes, the water expands, and the ice pushes up against the EIFS and can sometimes shear off the bottom edge of the EIFS.
Sometimes, EIFS is integrated with other materials on chimneys. For instance, to get a Tudor look, wood can be added to "frame" the EIFS. When doing this, make sure to carefully seal the interface between the wood and the EIFS. These materials expand and contract at different rates and can be a source of water entry. The same applies to real stone, which is sometimes used as an accent. Architecturally, real stone and EIFS make a dynamic contrast, and can look really attractive, especially using some of the thin veneer stones like those found in Texas and in Pennsylvania (field stone). Do not try to glue stone to EIFS. Stone is too rigid and heavy and will fall off. Instead, you'll need to attach the stone directly to a structural material back in the substrate, such as by using metal anchors or lath, with some type of weather-resistant barrier to keep the water out.
Lastly, EIFS can be applied to existing chimneys. As long as the surface is flat, sound and uncoated, EIFS can be attached directly to brick, stone, stucco and unit masonry using an adhesive. If the existing surface is not flat, try shooting metal lath into the substrate and apply the EIFS foam to the lath using an adhesive. One can also flatten-out an irregular substrate using lath and stucco and a scratch-plus brown coat.
Using EIFS on chimneys has lots of advantages. Aside from integrating the look of the main walls with that of the chimney, it also saves weight, and hence the foundation costs to support heavy chimney and firebox materials like brick and masonry.