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What size air conditioner is right for my mobile home?
Saturday, July 28, 2018
Most mobile homes have a “package” HVAC system for heating and cooling. The entire system (condenser, air handler, evaporator coils) is contained in one large box installed up against or near the skirting of the home. Package units are rated in tons of cooling capacity by air conditioning contractors, and a ton is equal to 12,000 BTU (British Thermal Units).
If you look on the manufacturer’s data plate inside the home, it will specify the recommended maximum BTU’s of capacity recommended for installation. Don’t know what a data plate is or where to find it? Click on this link to read our blog about mobile home data plates, then come back and continue: ”How do I find out how old a mobile home is and who manufactured it?"
On the right side of the data plate, under “Comfort Cooling,” you will find the manufacturer’s maximum recommended BTU number. To convert the BTU’s listing on the data plate into tons, divide by 12,000. So, for example, a recommendation not to exceed 38,743 BTU (as shown above) would mean not to install larger than a 3 ton, or maybe 3-1/2 ton system.
Larger is not necessarily better when selecting an air conditioning system for your mobile home. The air conditioner serves two functions simultaneously: cooling and dehumidification. But when the a/c system is more powerful than the manufacturer recommends, the home is cooled down too quickly, and not enough air volume flows over the system’s cooling coils to remove sufficient moisture from the air to bring the indoor humidity down to a comfortable level. Homeowners with oversize a/c systems often try to solve their high indoor humidity problem by lowering the thermostat setting further, but a very cold thermostat setting can cause condensation to form at the registers (louvered vents that supply air to the rooms), compounding the problem further. The warning label, shown below, is one manufacturer’s attempt to help their home owners avoid installing an oversize system.
Since every degree that you lower the thermostat setting increases your cooling bill from 3 to percent, a system that has a high efficiency rating, but an inadequate dehumidification rating, may cause you to have a higher cooling bill.
Here’s three questions that the Florida Department of Community Affairs recommends that you ask your air conditioning contractor:
- Can you do a load calculation in order to size new equipment properly to my structure?
- Does the equipment you are proposing meet Florida’s current efficiency requirements?
- Since moisture control is so important for Florida’s climate, can the proposed equipment maintain an indoor relative humidity of 55 percent or below?
If the data plate is missing or painted over, there is another option. You can download the Manufactured Home Cooling Equipment Sizing Guidelines, which includes a calculator chart produced by the Manufactured Housing Research Alliance in conjunction with the U.S. Department of Energy’s Energy Star program. Click below to download:
First, measure the exterior of the manufactured home to calculate the square footage, then find the “sizing group number” for the location of the home in the set of attached maps and, finally, look up the recommended tonnage on the chart for the combination of the two variables. There are two recommended tonnages for each combination: the first one is the size for Energy Star rated manufactured homes (with upgraded insulation), and the second is for homes manufactured to HUD standards beginning in October 1994.
Mobile homes manufactured before October, 1994, met a lower insulation standard and are not included in the chart. For older homes, we recommend consulting a licensed HVAC contractor.
Also, see our blog “What is the best air conditioner for a mobile home?” for advice on selecting the right type of air conditioner.
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