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Posted on July 9, 2020

[dropcap]O[/dropcap]ne of the questions we get as HVAC professionals is about installing central air conditioning in older houses. Many houses on the East Coast, and in Erie where our headquarters is located, were built 100+ years ago. It is entirely possible to successfully retrofit these historic structures without losing the integrity of the house, but there are a few things to keep in mind.

Some older houses are easier to retrofit than others. If the house already has a forced-air heating system, the new AC unit can simply utilize the existing ductwork. These retrofits tend to be quick and inexpensive. For example, to add air-conditioning to a forced-air heating system for a 2000 square foot home, it can cost as little as $3,400 and can be completed by two technicians in one to two days with little or no change to the ducting.

If the house requires new ducts, these costs will increase (and probably double) because contractors will need to retrofit the ductwork behind walls and in other areas where they can find space.

Whether you need new ducts or can use existing ductwork, there are certain considerations you need to make when installing central AC.

1. How Much Cooling Do You Need?

The first thing you need to determine is cooling capacity and efficiency. This can be determined by a contractor based on a load analysis using the Air Conditioning Contractors of America Manual J.  In addition, the contractor will consider certain specifics relating to the construction of your particular home such as surface areas of exterior walls, insulation levels, window glazing and air filtration. Cooling capacity is measured in BTU’s and the amount needed is determined by the above factors.

Getting just the right size is important for your AC to function properly. If the unit is too large, it will cool your space very quickly, minimizing air circulation and reduction of humidity. Humidity reduction is one of the advantages of air conditioning and is important because reduced humidity can actually increase your comfort level at higher temperatures, meaning a 75 degree home at low humidity will feel cooler than a 75 degree home at higher humidity and therefore put less demand on the AC unit. A unit that is too small, on the other hand, might always be running and will therefore create a higher energy bill.

2. Unit Efficiency

Unit efficiency is measured in SEER or Seasonal Energy Efficiency Ratio.  SEER measures how much money the unit will save vs. the number of years it will take to break even. Air conditioners with a SEER more than 12 will have a decent cost savings scenario but buildings with loose windows, doors, and gaps around the base boards and moldings can have air leakage and spillover, including moisture if you’re in a humid environment. Sometimes air conditioners with even higher SEER could make sense but this would depend on the length of the cooling season and how often the unit would be used. The energy savings and payback will be different if you’re only using AC two months out of the year (such as in Erie, PA) vs. seven.

Once you have an idea of how much cooling your home requires, you can decide what type of AC unit you need.

(Condenser for Central AC Split System)

3. What Type of AC Unit Do You Want?

There are two main types of AC units and then variations from there.  There are Package Systems. These systems combine the condensers along with the fan-and-coil system into one unit. This is similar to a large window air conditioner and not very common.

The other alternative is a “split system.” In these types of systems, the condenser is outside the house and the fan-and-coil system is inside. These two parts are connected by pipes carrying refrigerant.

4. Ducts! What If You Don’t Have Them?

As mentioned above, many old houses do not have ducting. When this is the case you can either…

Install new duct work: The ability to install duct work is determined by the individual characteristics of your house. The majority of older houses have plaster walls and detailed finishes which requires extensive clean-up afterwards. In this situation, ducts are often added in closets or ceilings, but sometimes, given the way the home is constructed, this is not an option, which leads us to the next possibility…

(Wall Unit for Ductless Mini-Split System)

Ductless Mini-split System: Mini-splits are heating and cooling systems that allow you to control the temperatures in individual rooms or spaces.

Mini-split systems have two main components — an outdoor compressor/condenser and an indoor air-handling unit(s) (evaporator). They are easy to install and usually require only a three-inch hole through a wall for the conduit; which houses the power and communication cables, copper tubing, and a condensation drain line, linking the outdoor and the indoor units.

Mini-split heat pumps are not only great solutions for whole home or new constructions but make good retrofit add-ons to houses with “non-ducted” heating systems, such as hydronic (hot water heat), radiant panels, and space heaters (wood, kerosene, propane). They can also be a good choice for room additions where extending or installing distribution ductwork is not feasible, and energy efficient new homes that require only a small space conditioning system.

Whatever options you decide to do, the HVAC team at Wm. T. Spaeder is here to guide you in choosing the best system for your house as well as installing it quickly and professionally. If you have any questions, give us a call at 814.456.7014 or email We look forward to hearing from you!


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