Frequently asked Questions
1) My house has a 3 ton unit now. Can I upgrade to a larger unit outside to get more cooling without changing the indoor heater?
A: Not that easily. The indoor and outdoor units have to match within limits in air volume, and coil surface area. That is to say, you may be able to put a 3.5 ton system on a 3 ton blower and coil, but you still will not get the capacity or efficiency of the new 3.5 ton unit. Also, you need your AC system matched closely to your real load to get effective humidity removal. An oversized system will run too little in Spring and Fall to get your humidity in control, so you will find yourself setting the AC really low to feel comfortable. If your existing system isn’t keeping up, it’s more likely that it is tired and producing 60% of it’s original cooling, not that it was too small to start with. I rarely recommend customers to increase the size of their original systems The only way to tell for sure is with a design load calculation.
2) My house is 2500 sq ft. How many tons of AC do I need? .
A: No real good answer to tons/sq ft. Home design, interior loads, location, insulation, windows, air tightness and much more goes into the actual heat gain/loss of a structure. The only good way to analyze a structure is by doing a heat load on the building. Better yet is a room by room analysis , so the final air flow to each room can be determined into the design.
On the other hand, with 90% of homes built the design and balancing of the system is left to the field installer who is left to install on site the what he has on the truck. Of course, many have learned enough to have “gut” feelings, and can do a fair job without proper calculations.
All that said, some general rules of thumb: Older homes (60’s to 70’s) with poor or minimal insulation, figure 450-500 sq. ft/ ton. Better built (80’s to 90’s) with more insulation, more airtight….figure 500-600 sq ft ton. Newer homes, 2000+ should be built more airtight, with low e windows, can achieve up to 700 sq ft/ ton. Remember, these values are estimates for the South Texas area, not nationwide. See our info pages on “Saving Energy”.
3) Is one brand really that much better than another?
A: Yes, but not that much. I will avoid naming any brand names, but will say that most brands use very similar components from the same suppliers. There is a difference in thickness of metals, paint quality, number of fasteners used to assemble, and even in the quality of electrical components. Also, warranties vary, as well as customer service. Trane/American Standard builds many of it’s own compressors, while most all the other brands purchase from other companies. More than the unit itself, the quality of the installation is a factor, and lower priced contractors tend to provide poorer service and cut installation steps along with selling lower priced units.
4) Do I have to replace my indoor evaporator coil if I replace the outdoor unit?
A: Generally speaking, yes. Most older coils are designed to operate on the lower pressure R-22 refrigerant, which is now no longer available in new equipment and are not rated for the new R410A.. R22 also uses mineral oil, instead of newer synthetic oils , so the coil would have to be flushed well to avoid contamination. To get the rated efficiency from a new unit, it should be matched to the indoor coil it is tested with by AHRI.
5) Can I mix brands of units….say Trane outdoors, and Rheem furnace?
A; Sure. As long as the factory rated capacities are reasonably close, they will work fine together
6) Does efficiency make that much difference? What is the difference between 10 seer and 13 seer?
A) It makes a big difference. The number is relative to the seer rating. Thus a 13seer unit is 30% more efficient than 10 seer. A 20 seer uses half the power of a 10 seer! Seer stands for Seasonal Energy Equivalent Ratio. In takes into account the average daily outdoor temperature, which affects the efficiency, instead of just calculated based on a certain fixed outdoor design temperature. The minimum standard for newly installed equipment is now 13 seer, which just a few years ago was considered high efficiency.
7) What is best for heat, Gas, electric heat or heat pump?
A) Easy. Simple answer is cost to operate. If gas is available, it is least expensive to operate. Heat Pump is best if not gas is available. Straight electric heat (red hot heat elements) are so expensive to operate it’s scary. Luckily, our heating season is short, so electric heat is not out of the question. Cost to install? Least to most: Electric heat, Gas, Heat Pump. The cost difference should not be more than a few hundred dollars one way or the other, so the choice should be gas if available, then heat pump. If you want real energy savings, see our section on Geothermal AC and Heat which beats them all in efficiency.
8) Which is better R22 refrigerant or the new R410A for my home air conditioning?
A) As of Jan 1 2010, no more R22 equipment is being manufactured. R22 refrigerant, which has been around in common use for 70 years, is being phased out as a result of the Montreal protocol, a series of discussions and agreements in the early 1990’s between many nations with the idea of reducing greenhouse gases that may be damaging the Earth’s upper ozone layer. As a result, R22 based equipment is phased out of production in 2009, and the gas itself is phased out 2015. After then, reserves will be in place for years.
R410A has been designed and is generally accepted as the replacement gas that is not destructive to the atmosphere. It operates at higher pressures than R22, had some oil delivery issues, and initially was not as efficient as R22, but engineering has overcome these problems as expected. R410A was initially much more expensive than R22, but since the early days it’s price has fallen, and R22 has risen, to about triple the cost of R410a as of Jan 2013.
Since R22 units are no longer in production, a failed outdoor unit will mean it will also be necessary to replace the indoor coil, with a matching R410a rated unit., or if you have electric heat, the entire indoor air handler.
9) Should I just get the most efficient system I can afford? How fast will it pay back?
A) Like with everything else, efficiency has it’s points of diminishing returns. That is, it may be difficult to determine the time/expense savings of a super efficiency system vs. standard 13 seer. Suffice to say, that a 16 seer system should save about 20% of power related to your AC bill. Typically this means 15% per month off your bill during high cooling months. Of course, if your old system is a tired 9-10 seer system, (typical from 10-12 years ago) your savings with a 16 seer would be closer to 50%. On average, expect 4-7 years to payback in power savings, to recover the additional expense of a 16 seer system. For super efficiency, a 30% rebate, and super comfort levels, try geothermal.
Conventional AC and Heat
Answers by Mark Smith : 30 yrs HVAC Service and Installation
License holder for Allied Air Texas TACL B15309C
Allied Air Texas
Serving the greater Houston, Texas area, including Tomball, Spring ,Cypress, Waller, Magnolia, Montgomery, Conroe, The Woodlands, Willis, Kingwood, Crosby, Huntsville, Galveston, Pearland, Brazoria, Sugarland, Richmond, Katy,