Construction Design-Mechanical Room

This post first appeared on the Green Building Advisor website.

I’m one of those nerds that politely tour a new home looking at all the fine trim work and fancy finishes, but secretly can’t wait to get the mechanical room.  (Sometimes I even have to ask to see it.)  If that room is well laid out and neat, I feel I’m in a quality home.  It’s been a few years since I’ve worked full-time as an electrician, but I still remember the frustrations of being on a new build or working in an older home where there just wasn’t enough space in the mechanical room for all the equipment.  The trades working together (more often fighting) for that last piece of wall space to fasten their equipment is something I experienced many times.

My market is full of older homes that have simple mechanical rooms, sometimes the mechanical room was the entire basement.  Heating (and sometimes cooling) forced air system, a water heater and an electrical panel was often the only equipment present.  They didn’t need many square feet to fit the equipment.  A new, modern home may have different requirements.  Multiple electrical panels are common.  Air source heat pump and large or multi tank electric storage water heaters take up more floor space than the old 40-gallon natural drafting gas units.  Many homes in my climate have multiple heating systems, it’s not uncommon for a new home in my market to have both a forced air and an in-floor hot water heating system.  More space is required for an ERV/HRV unit.  Water conditioning equipment and well pump pressure tanks can also be present.  On top of that, upper end homes can have data and communication gear and racks taking up even more room.  New basements are often finished living space, carving out the space for the mechanical room can be tough.  I often see slab on grade homes with mechanical rooms accessed off an attached garage.

Dual electric water heaters supply extra hot water capacity when installed on an electric load management program.

Electrical Equipment

Because I worked for several years as an electrician, lets first talk about electrical equipment.  Article 110-26 in the National Electric Code (NEC) and E3405.1 in the International Residential Code (IRC) both cover working space requirements for electrical equipment.  The code states:

Access and working space shall be provided and maintained about all electrical equipment to permit ready and safe operation and maintenance of such equipment.

Makes sense, don’t position an electric water heater so the thermostat and element access panels face a wall or other obstruction.  At some point someone will need to service that equipment, the code wants that person to remain safe while performing the task.

Electrical service panels or breaker boxes have large working space clearance requirements.  36 inches out from the face of the panel.  The width is the width of the equipment or 30 inches, whichever is larger.  The clear space continues to a height of 6 foot-6 inches or the height of the equipment, whichever is taller.  At a minimum, the space in front of an electrical panel will be 30 inches wide, 36 inches deep by 6 foot-6 inches tall.  If there are multiple electrical panels grouped together, the width of the clear space will increase to the width of the equipment.  I’ve been in homes with four service panels grouped together on the same wall, the clear space width was 64 inches by 36 inches deep by 6 foot-6 inches tall.  Nothing other than electrical equipment can be in this space, no framing, no ducts, no waste or vent plumbing piping, and no water lines.  These requirements are for systems with 150 volts or less to ground.  It’s uncommon that an electrical system for a residential home is over that voltage.

In addition to service panels, there may be other electrical equipment that needs space for installation, servicing and eventually, replacement.  Equipment for solar arrays, battery storage systems and other associated equipment may all be present.

This photo shows several code violations, the electrical panel does not have the required clear working space, the clothes washer impedes access and presents a shock hazard.  Someone working on the panel will be in contact with the grounded dryer.  There is a water line directly above the panel within the 6’-6” height.  In addition, the water heater was installed with the access to the thermostats and elements turned towards the cast iron waste piping.  A poorly thought-out space.

Mechanical Equipment

In addition to the electrical working space requirements, the mechanical equipment, or appliances also have space needs.  The required space around mechanical equipment is found in the IRC M1305.1 code section.  The code state:

Appliances shall be located to allow for access for inspection, service, repair and replacement without removing permanent construction, other appliances, or any other piping or ducts not connected to the appliance being inspected, serviced, repaired or replaced.  A level working space not less than 30 inches deep and 30 inches wide shall be provided in front of the control side to service an appliance.

Before we go any further, let’s look at the definition of an “appliance” according to the IRC.

Appliance.  A device or apparatus that is manufactured and designed to utilize energy and for which this code provides specific requirements.

So, according to the code, an appliance is a water heater, force air furnace, boiler, HRV/ERV, water softner, etc…all these pieces of equipment require a minimum of a 30-inch by 30-inch clear space to maintain, service or replace the equipment.  These spaces are allowed to overlap.

The code goes on to say that the room where the equipment is located needs an unobstructed passageway of at least 24 inches or large enough to remove the largest appliance located in the room.  In my opinion, 24 inches is not a large enough passageway.

Mechanical room location within the home

Many of the house plans I review have some area inside the home or garage where these mechanical systems are planned to be located.  Depending on the systems planned to be installed, it’s often beneficial for the mechanical room to be located on an exterior wall.  It’s best, and sometimes code required that the service conductors feeding the electrical panel, which are often not overcurrent protected, do not travel for a distance into the home through framing.  Short line sets for air conditioning and heat pump systems are easier to work with than ones that need to travel across a building. It can also be easier to sleave for a water or sewer line through a basement wall rather than excavate under a footing and concrete slab for any distance.  Communication systems (phone, cable and internet) from providers can change over time, fishing new wires or fiber optic cables across a finished building can be difficult.  For these reasons, I try to locate mechanical rooms on at least one exterior wall.

Multi-purpose mechanical rooms

Often mechanical rooms end up being used for multiple purposes.  I’ve been in many where the laundry appliances or an extra refrigerator or freezer are located in the same room as the heating and cooling, water heater and electrical equipment.  I’ve also seen the space used for storage.  When designing these rooms, it might be a good idea to have a conversation with the homeowner about what they may want to do with the room.  Too many things stored in the room may restrict periodic maintenance of the equipment, such as changing filters on force air and ventilation equipment.

An example of a mechanical room having multiple purposes.  This homeowner dressed up the forced air furnace with a decal to “improve” the room’s looks.

Other Design Considerations

Certain appliances and equipment may have specific volume requirements.  For instance, fossil fuel combustion equipment that uses indoor air for combustion may require a room with a larger volume or a combustion air vent or undampened duct directly to the outside.  Most new construction I see uses sealed combustion appliances that take their combustion air from outside, but I do occasionally see the lower efficiency fossil and solid fuel appliances.  (By the way, the blower door testing standard used for the IRC will not allow these combustion air ducts be sealed during a code compliant blower door test, that 6-inch hole to the outside will affect the blower door score.)

Another appliance I see occasionally that require additional volume space is an electric storage furnace.  These off-peak all electric storage heating systems can greatly affect the temperature in the space.  I’ve been in a few mechanical rooms where the ambient temperature of the space in the middle of winter is more than 80°F.  (This is the ideal location for an air source heat pump water heater.)  These all-electric furnaces are quite large and heavy.  It’s important to know the manufacturer requirements of the equipment being installed before designing the space.

Steffes Electric Thermal Storage Furnace (ETS)

One last consideration, a code dealing with mechanical rooms off attached garages, M1307.3 in the IRC states:

For the purpose of this code, rooms or spaces that are not part of the living space of a dwelling unit and that communicate with a private garage through openings shall be considered to be part of the garage.

This is important because appliances that have an ignition source located inside a garage, the ignition point must be elevated to a minimum of 18 inches above the floor.  Gas water heaters and forced air furnaces may need to be raised to meet this code requirement.  In my area, it’s common for the mechanical room off a garage to only be accessed from inside the garage.  This is one of those codes that should be discussed with your local AHJ.

The climate and area you live often has the “normal” location for the mechanical equipment, hot climates often find HVAC systems in the attic (hopefully a conditioned attic.)  Crawlspaces may also be used, again, hopefully it’s a sealed and conditioned crawlspace.  In my very cold climate, basements and dedicated rooms are the norm.  I get it, floor space is valuable, but the mechanical room is often the most expensive room in the home.  Having enough space to safely and neatly perform the work of installing these systems can make a mechanical room just as impressive as a high-end kitchen or bath, though my opinion might be a little biased.

4 Replies to “Construction Design-Mechanical Room”

  1. Presently designing a small home with attached garage. It is my wish that the Mechanical room be located in the garage. I was told by a plumber that the room could not have a door opening into the garage and would have to have outside access and no access to the garage itself. Is this true and code enforced? I am in Northern Maine, planning oil fired radiant heat in a slab, on demand hot water as well as water softener etc… A heat pump will be added for summer cooling and emergency heat in the winter w/generator

    1. Hi Nancy,
      Unless there is some local code that says otherwise, I do not believe your plumber is correct. I would ask the plumber for the code reference or have a chat with a local building inspector just to make sure. Mechanical rooms off garages with access from inside the garage are fairly common here in Northern Minnesota. These mechanical rooms in my area are very well sealed from the garage space, this typically includes a well sealing exterior door into the space. The rooms are usually also outside the home’s envelope as well, they are also air sealed and often insulated between the home and the room. Basically, an air-tight and insulated room inside the house.

      Here is the building code that deals with general mechanical system requirements. Mechanical equipment is allowed in attics and crawl spaces, I would think having a room off the garage would benefit the plumber.

      Hope this helps,

  2. I’m having a tiny house built on a foundation with all-electrical equipment. I can’t find anything on what a mechanical room would look like or how much space I will need to set aside. I often see water heaters hung on walls but I don’t want my mechanicals to be visible.

    1. Hi Amy,
      Sizing will depend on what equipment is in the room. Forced air heating and cooling systems may take up some floor space, but then again, they can be hung horizontally from the ceiling. Electric water heaters can be designed as storage systems, but most all electric homes being built now are choosing heat pump water heaters. They typically measure a couple feet in diameter but can be a little taller than standard electric water heaters. Balanced mechanical ventilation systems, which are required in all new homes in Minnesota, are another ceiling or wall mounted piece of equipment. Rural areas may require a pressure tank for a well and water treatment systems to improve water quality.

      Tiny houses usually don’t have as much equipment as a full-size home, but you still have heating and maybe cooling, water heating and ventilation equipment that will be needed. Water heating may be satisfied by utilizing small, on demand electric water heaters placed under sinks, a shower or bathtub may have a little larger hot water need but could still be located under a bathroom sink. I’ve seen HRV/ERV’s designed for constant balanced mechanical ventilation designed into bath fans, I believe Panasonic offers a model. A tiny home could be heated using a cold climate mini-split heat pump (wall or ceiling mounted) for most of the year with an electric baseboard or cove heater used as backup during really cold weather. A well pressure tank can be buried at the well, then you just need to deal with water quality equipment, which will vary depending on needs. You might be able to get away from needing a mechanical room altogether if you choose the right equipment and design small spaces to accommodate needs accordingly.

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