The Hidden Kitchen Understanding the Structure of a Modern Kitchen

Putting together a kitchen is not a trivial process. Besides the obvious considerations: new cabinets, appliances, a new floor, and paint or wallpaper, there are many structural considerations.

The kitchen structure is hidden — behind cabinets, under floors, above ceilings — and not very pretty, but extremely important. Without adequate electricity, lighting, plumbing, heating, and venting — all the new cabinets and appliances won't result in a workable or safe kitchen.

So, let's take a look at kitchen structure.

Electrical Requirements

Almost all kitchens more than 10 years old are under-powered.

Electricians and builders of old simply could not predict the number of large and small appliances found in most kitchens today. Depending on the age of your house, you can expect only one or two receptacle circuits, with illumination pulled from a general lighting circuit powering all ceiling lights.

Electrical Requirements for a Home Kitchen
  Cir­cuit Pa­nel Slots 1 Notes
Lighting, Ambient 110v, 15 amp 1 General room lighting, usually with ceiling lamps.
Lighting, Task 110v, 15 amp 1 Work area lighting, generally undercabinet fluorescent or LED lighting.
Over Counter Outlets 110v, 20 amp 2 Even in small kitchens, two separate circuits to counter outlets is a good idea. In large kitchens, it may be required by your local electrical code.
Electric Range or Cooktop 220v 2 Gas range: 110v, 15 amp.
Wall Oven 220v 2 Gas wall oven: 110v, 15 amp.
Microwave Oven 110v, 20 amp 1 If combined with the range vent, both can use the same circuit.
Refriger­ator 110v, 20 amp 1  
Freezer 110v, 20 amp 1 Stand-alone freezer separate from the refrigerator
Trash Compacter 110v, 20 amp 1 Some localities allow the compactor to share a circuit with the disposer.
Dishwasher & Disposer 110v, 20 amp 1 Some localities require a separate circuit for each appliance.
Instant Hot Water Dispenser 110v, 2o amp 1 Some instant hot water dispensers require 220v power.
Total  14 2  
1. Slots required in your service panel. A 220-230v circuit requires two service panel breaker slots. A 110-120v circuit requires one.
2. The total number of circuits required for the typical modern kitchen nearly equals the number needed for the whole house just 50 years ago.

Most older kit­chens also do not have ground-fault-protected circuits that are absolutely required by safety codes today. Ground-fault circuit interrupters (GFCI) outlets help to avoid accidental electrocution by shutting off the electrical current if you accidentally touch a live wire. According to the National Electrical Code, all outlets within 6 feet of a water source and all receptacles serving kitchen countertops and islands must have GFCI protection. The best practice, however, is to GFCI-protect all kitchen outlets.

In a complete kitchen overhaul, upgrading the wiring is fairly easy, if there is enough room for new breakers in the service panel. Often the panel is too small. Lacking enough room for expansion, a panel and service upgrade is a must. The job will run $600 to $1,200 in most markets and is always money well spent.

As for powering a new kitchen, large appliances that produce either heat or cold need dedicated circuits. This includes the refrigerator, microwave, and dishwasher, although in most areas it is permissible to combine a dishwasher and food disposer on one circuit.

Avoid plugging a computer into a circuit that is serving a spike producing microwave oven — unless you just like the interesting on-screen effects. Electric ranges, cook-tops, and ovens each require a 220-volt circuit.

If your kitchen is large enough, try to power the above-counter receptacles with two 20-amp circuits. These usually serve small appliances like blenders, coffee makers, and microwaves that will appreciate the extra power — and show their appreciation by not overloading and tripping the circuit breaker.

The best practice (not always followed), is to power every other outlet above a countertop from a different circuit. This ensures that at least some outlets have power if one circuit fails, something that only seems to happen when you are in the middle of fixing Thanksgiving dinner.

Most electrical codes require an above-counter duplex outlet a minimum of every four feet — closer is better — and it usually costs very little more to install four-plex rather than duplex outlets, doubling your plug-in capacity.

As a general rule, when in doubt, and when possible, provide more, not less electricity. If the last 50 years are any guide, the kitchen of the future will require even more power than today's kitchens.

If you have an appliance garage, include an outlet or two inside the garage. The allows you to leave the appliances plugged in so you need only pull them out to use them.

Outlets inside cabinets can power a television and stereo equipment. Consider your lighting needs too. That dark cavern under the sink can be well lit by a 40-watt bulb in a simple pull-chain fixture under the sink.

Kitchen Lighting

Most kitchens are poorly lighted. The light from a single fixture centered overhead is usually blocked by your own body as you work at the counter. Wall cabinets also block overhead light, leaving the primary food-prep spaces darker than the rest of the room.

It's not just the age of the kitchen that matters — it's also the age of the cook. Experts say that people over the age of 50 require at least twice as much light to read than when they were 20. The solution? More versatile, task-oriented light in more places.

Under-cabinet lights can make a big difference. Today these are LED fixtures that cost very little to install and operate. LEDs use much less electricity for the same amount of illumination produced by old-style incandescent and fluorescent fixtures, and, as a bonus, last several times longer than their older cousins. Not every wall cabinet will need a light, but those nearest your primary work­spaces should have them.

Recessed ceiling fixtures are also popular for general room lighting. They can be spread out to direct light to every corner of the room. If you live in a single-story house, opt for the slightly more expensive zero-clearance models. These can stand direct contact with attic insulation. Fixtures that are not zero-clearance need ventilation to keep the lamps and wiring cool, and if surrounded by insulation may bet hot enough short the fixture or, worse, start a fire.

Cove lighting is another popular option for general illumination. Inexpensive (usually fluorescent) fixtures are installed on top of cabinets aimed at the ceiling. The light reflected off of the ceiling illuminates the room with an even, soft glow. To aid the process, we usually install a reflective foil surface on the top of the cabinets.

Line voltage (110v) fixtures are declining in popularity. The small but mighty low-voltage LED alternatives are gaining ground pretty quickly. Their advantages are compact design, energy efficiency, and a certain minimalist understatement.

Some fixtures are so compact that they fit invisibly beneath wall cabinets and even inside dinnerware and curio cabinets. Many have built-in voltage-reducing transformers, while in other cases, several fixtures are ganged together. A 100-watt transformer, for example, could serve five 20-watt lamps. Some of the small fixtures come in strip light form, with lamps in fixed positions.

When planning your lighting, keep in mind that the old standard Type-A incandescent light bulb is now banned. The alternatives are compact fluorescent and LED bulbs designed to fit in a Type A (or Edison) socket.

Kitchen Lighting: Read more about efficient kitchen lighting design in Designing Efficient and Effective Kitchen Lighting.

Kitchen Plumbing

IF your kitchen remodel does not require moving your sink, you may get away with just minor plumbing changes that do not involve piping in the walls, floor, or ceiling. Extensive kitchen remodels, however, usually require some change to plumbing and ventilation piping. Unless your changes will be minor, this work requires the assistance of a professional.

The piping in your kitchen may also in bad shape. If your kitchen is over 50 years old, it's a good bet that the original piping was made of galvanized steel, an excellent product with a long lifespan. But it is now nearing the end of its useful life and time to replace it with plastic, which, as far as we know, lasts forever.

There is also close to a 100% chance that the original plumbing does not meet current plumbing code requirements. Any time you touch kitchen plumbing, you are going to have to bring it up to the current code. In most localities, this is true even if you otherwise would not need to disturb a pipe. But, irrespective of code requirements, it's always better to update plumbing while the room is empty and the walls open rather than waiting for the very expensive repair that is sure to come a few years down the road if deteriorating plumbing is left in place.

One of the common plumbing problems we find is a badly sloped drain line. The ideal slope for any horizontal drain line is 1/4" per linear foot. This much drop allows the waste-bearing water to move slowly enough to carry solids along with the flow but swiftly enough to scour the sidewalls of the drain pipes. We find slopes as little as 1/16" per foot, which almost guarantees clogging and periodic emergency calls to the plumber.

Over-sloping is also a problem and a common mistake made by DIY plumbers (is some slope is good, more slope is better, right?). Slopes much greater than the ideal 1/4" are as likely to clog as under-sloped pipes because the liquids move too fast and leave the solids behind. Proper sloping is critical with a disposer dumping solid waste into the drain system.

Inadequate drain venting is another frequent problem. Drain pipes must be vented to the atmosphere outside of the house to work properly (not to be confused with room venting, discussed below).

It's easy to illustrate the problem caused by inadequate venting using the "Pepsi Challenge".

Pop the top on a can of Pepsi and turn it upside down to drain. It will drain with a glug-glug-glug sound. As the liquid drains a vacuum is formed at the top of the can (or bottom of the can since it is now upside-down). Nature abhors a vacuum and tries to fill it with something. The only thing available is air, so air is sucked up into the can through the only opening available — the same hole through which the soda is draining. The brief pause between one glug and the next is the air entering the can. Now take your handy awl from your toolbox and punch a small hole in the top (actually the bottom) of the can. The soda immediately pours out in a rush. Air now has an easier way of getting into the can through the small hole you just made, so it no longer has to fight with the liquid to use the drain hole.

Venting in your plumbing system works exactly the same way. It allows air to enter the system to fill any vacuums created by draining liquids. And, perhaps most importantly, it allows any methane that builds up in your drains to escape safely to the outside. Methane is just natural gas without a bad smell. In fact, it is odorless, and since it is very flammable and can easily explode, it is also very dangerous.

This is why modern plumbing codes no longer permit venting directly through a wall (the gas may be sucked into an upstairs window) or into the attic. If enough accumulates in the attic, it may explode. Vents must terminate outside and above the roofline.

Many older kitchen sinks were vented through a drain from an upstairs bathroom. This is not a good method. As in our Pepsi example, if water is draining from upstairs, the air and water are fighting for space in the drainpipe, so venting is inadequate. Most plumbing codes no longer allow these "wet vents" except in exceptional circumstances, so we have to add a vent for the kitchen sink that does not share a pipe with water.

If you install an island cabinet with a sink, the drain line serving that sink often cannot be vented conventionally. In this case, an automatic-vent device or a barometric (loop) vent is required. A licensed plumber will know which is best for your situation. In Nebraska, and many other localities, automatic vent devices are not allowed because they tend to fail after a few years.

Room Ventilation

Changes in the house heating and air conditioning systems are usually not required to remodel a kitchen in an existing space. But if a bump-out or addition is built, then additional heating and cooling may be required.

Sometimes, the only solution is to upgrade the whole house system, which can get a little pricey. But this is rare. What we usually do is add a supplemental system on its own thermostat to heat and cool the additional space. The new kitchen "zone" can be controlled separately from the rest of the house, which is nice when the oven is pouring out heat on a summer day.

What will almost always be required, however, is a new exhaust vent over the cooking surfaces. Few older exhaust systems meet current building code requirements, and building code requirements are themselves probably inadequate to ensure that modern kitchens are well vented.

Exterior Venting

Install a range hood that vents to the outside. Cooking on a range or cooktop releases ultra-fine particles of grease, water, smoke, and food into the air that land everywhere, which explains the grime that accumulates on cabinets, floors, and fabrics.

The notion that a ventless (recirculating) range hood can actually trap the estimated 200 lbs. per year of particulates produced by cooking in the average kitchen is just plain nonsense. Nor do they exhaust the humidity produced by cooking or the chemicals that may result from the incomplete combustion of natural gas, producing nitrogen dioxide which has been shown to cause respiratory problems, including asthma, especially in children. Most building codes now require venting to the outside, either through a wall or the roof. Through the wall venting has a number of restrictions, so check your local building code.

Venting Capacity

A kitchen vent hood should be able to completely exchange the air in your kitchen at least 15 times each hour or once every 4 minutes. The capacity of the kitchen vent fan required is based on the size of the kitchen, the maximum amount of heat produced by the range or cooktop, and the length and configuration of the ductwork. It's a fairly complicated calculation that an HVAC contractor will complete before recommending a minimum capacity.

The length and configuration of the ducting used to exhaust the contaminated air to the outside determines how much venting capacity is required. A long pipe requires more force to move the air through the pipe and additional force is needed for each bend in the pipe. For example, when using smooth, round 8" diameter metal pipe, one cubic foot per minute (CFM) of fan capacity is added for each foot of pipe, plus 25 CFM for each elbow, and 40 CFM for a roof cap.

Research by the University of Minnesota's Sustainable Housing Initiative has shown that most existing range hoods are too small, too high, and not oriented properly to do their job.

The most effective hoods are at least as wide as the cooktop, preferably wider, extend at least 20" beyond the front edge of the range, and are rectangular rather than angled or curved in front. Most wall-mounted hoods extend no further than to the center of the front burners, considerably less than the projection recommended by the study.

Consumer Reports recommends that an island microwave be at least 6" larger in each direction than the cooktop or range it vents. Few hoods designed for residential kitchens meet these minimums.

Downdraft vents are even more problematic. They work by pulling the air sideways across the cooking surface and drawing smoke, steam, and grease down through a filter and into a duct that carries it beneath the floor to an exterior vent. To be effective they must struggle against the natural tendency of warm cooking gases and particles to rise. Most project about 10" above the cooking surface and without a hood to capture steam and gases and direct them to the fan, they rely on a large fan capacity to work well.

Hoods that are integrated with microwaves mounted over the range are a particular problem. These typically extend over Just the back half of the range and miss most of the contaminants generated by front burners. Consumer Reports found that none of the microwave vents tested for its most recent report were top-rated for effective ventilation. One solution is to enlarge the capture zone by installing an extension that attaches to the front of the microwave.

The Home Ventilating Institute (HVI) recommends a ventilation rate of 100 CFM per linear foot of range placed against a wall and 150 CFM when placed above an island.2 These levels will ensure that enough air is being pulled from the system to help maintain healthy indoor air quality. A typical 30" range (2.5 feet) should vent at a rate of 250 CFM.

Generally, local building codes require at least 150 CFM, and most areas require makeup air if the capacity exceeds 350 CFM. This may include a servo-operated intake vent located (usually) in the basement that automatically opens when the fan is turned on to admit enough fresh air to make up for the air being exhausted to the outside.

Advanced Ventilation

Consider two useful ventilation features: a heat recovery system and automatic vent operation:

Kitchen Design Guidelines

Structural considerations are a major part of any designer's kitchen planning. Many are contained in the Kitchen Design Guidelines published by the National Kitchen & Bath Association. Starting in 1944 the University of Illinois conducted several kitchen design studies and developed fundamental design principles that are still very much in use today. A kitchen that follows all of these rules is almost guaranteed to be both functional and safe. See how many rules your existing kitchen violates for a better understanding of why it may seem awkward and dysfunctional… (Continues)

Rev. 10/20/20