Energy efficiency is beneficial for any building, reducing monthly operating costs and contributing to environmental sustainability. However, in the case of pre-war apartments there are many practical benefits as well: these apartments have very old installations, and performance issues are less likely if load is minimized.

As implied by their name, pre-war apartments are those built before World War II, when engineering practices were very different from those of the present day. A key difference is that materials were much more expensive one century ago, while labor cost were very low. Therefore, it made sense to make constructions very sturdy and long-lasting, and remodelations were a less common concept. This trend has now reversed: materials are much cheaper, but labor costs have increased drastically, especially in a place like New York City. Thus, modern buildings are designed for fast construction, and are therefore easier to renovate.

Electrical rough-in in a modern apartment is very easy, since there are often many hollow spaces inside walls, ceilings and floors. On the other hand, pre-war apartments are not conceived to be taken apart easily, with monolithic floors and walls that are very difficult to break open for conduit installation. This is not only time-consuming and expensive, but can also ruin the look of a pre-war apartment unless the owner has a high enough budget to restore the original appearance.

Modern Appliances with Old Electrical Installations

The electrical wiring in a pre-war apartment is generally unable to handle the load produced by modern appliances, especially air conditioning units. However, even though society used fewer electrical devices 80 years ago, they were also much less efficient devices. As a result, using more electrical equipment in a pre-war apartment is possible if the equipment is selected as efficient as possible.

Another recommendation is to use 220-volt appliances whenever possible, instead of 110V. Remember that electrical wiring is not sized based on power, but current - if voltage is doubled current is halved, even when the power consumed by the appliance stays the same.

It is true that energy-efficient devices involve a higher price, but using appliances with standard efficiency will likely require an electrical wiring upgrade, and in many cases this is a more expensive option. Going for energy efficiency is better, reducing power bills in the long run without the risk of ruining the fine details of a pre-war apartment.

Assume a pre-war apartment requires air conditioning with a capacity of 12,000 BTU/hour (1 ton of refrigeration). If a conventional window-type unit or a packaged terminal air conditioner (PTAC) is used, the unit is likely to consume around 1,000 W. If the apartment is using ten 60-W incandescent bulbs, the total air-conditioning and heating load is 1,600 W. However, consider an alternative approach based on energy efficiency:

  • The 60-watt incandescent bulbs are replaced with 10-watt LED bulbs, reducing their total load from 600 W to 100 W.
  • A ductless mini-split system is used for air conditioning, with a Seasonal Energy Efficiency Ratio (SEER) of 28. If its capacity is 12,000 BTU/hour, its average power consumption will be 429 W.

In this case, the new total load of lighting and air conditioning would be 529 W, which is lower than the previous lighting load alone - 600 W. In this case, the pre-war apartment circuitry would have no problem accommodating air conditioning, since the load is actually lower.

Of course, building envelope performance is also important. Owners of pre-war apartments should check the building envelope for air leaks, which can cause extra heat gain during the summer and additional load on air conditioning systems.

Equipment Selection Tips for Pre-War Apartments

Many pre-war apartments have incandescent lighting, and their natural warm glow is part of the ambiance. LED lighting is often criticized for its “artificial” lighting effect, but this is not a common characteristic of all LED bulbs. The following guidelines are recommended to preserve the incandescent effect after a lighting upgrade:

  • LED bulbs should have a warm white color. In terms of technical specifications, this means they must have a correlated color temperature (CCT) below 3000 K.
  • Their color rendering index (CRI) should be as high as possible to mimic the natural lighting effect of incandescent bulbs. The highest CRI value is 100, and only incandescent and halogen lights can achieve it. However, the top LED bulbs offer CRI values above 90. Most commercial LED bulbs have a CRI above 80, while low-quality products may have values in the 60s or 70s, and are not recommended.

In general, home appliances with the ENERGY STAR label are recommended. They have undergone extensive testing by the US Department of Energy and the US Department of Environmental Protection, so energy efficiency is guaranteed.

With respect to space heating, space cooling and domestic hot water, the following table can help you select the equipment with the lowest energy footprint:


Efficiency Metric


Space Heating: Heat pumps

HSPF - Heating Seasonal Performance Factor

BTUs of space heating per watt-hour consumed, averaged for the entire heating season.

Space Cooling: Mini-split AC units and heat pumps

SEER - Seasonal Energy Efficiency Ratio

BTUs of space cooling per watt-hour consumed, averaged for the entire cooling season.

Domestic Hot Water (DHW): Heat pumps

EF - Energy Factor

Ratio of water heating output to electric input. Applies for any measurement unit as long as both output and input use it.

In the case of heating appliances, consider that most systems in New York City use natural gas, heating oil or district steam. However, heat pumps are also a cost-effective option for property owners who want to minimize the use of fossil fuels. Electric resistance heaters are generally not recommended due to their high energy consumption, and also because they can overheat old electrical wiring in pre-war apartments. For a given heating output, a heat pump generally consumes 2 to 4 times less electricity than a resistance heater.

Whole Building Benefits of Energy Efficiency

Another advantage of energy efficiency pre-war apartments is that savings add up for whole buildings. If many pre-war apartments in a condominium deploy energy efficiency, it is less likely that the property management company will have to upgrade the transformer, electrical service entrance and common wiring. These expenses are often allocated among occupants, so avoiding them provides a common benefit.

Final Recommendations

Like with any building upgrade, professional engineering advice is highly recommended before taking decisions. Property management companies can identify the most promising measures with an energy audit, and may be eligible for cash incentives from Con Edison. In general, the best results can be achieved with LED lighting, high-efficiency heating and cooling, and ENERGY STAR home appliances.

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