Freqently 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 such thing as 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.

3)          Do I have to change my inside coil to get 13,14 seer? 

A: No. But SEER Ratings are testing in certain coil/furnace/condenser combinations. So if your new outdoor unit is not tested with an older coil (which it will not be) the seer rating is unknown. Not to worry, a new unit with an old coil will probably not lose more than 3-5% with an unmatched coil, if anything. In any case, when you later replace the inside system the seer will meet or exceed the design of the outdoor unit.

4)         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 builds it’s own compressors, while 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.

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.

7) What is best for heat, Gas electric 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, has 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 an equal value as of 2009.

As a result, the cost and performance of a R410A system vs. R22 is generally about equal. The deciding factor in installation may be if you are replacing all your system or just a part. That is to say, you cannot replace a R22 condenser  with a 410A unit unless you replace the coil or air handler also.

As a result, the change to R410a often is a good time to replace your entire system, with new, high efficiency cooling and heat, instead of trying to make a partial system change out.

 

Conventional AC and Heat

Answers by Mark Smith  : 22 yrs HVAC Service and Installation

License holder for Allied Air Texas TACL B15309C

Got an AC or Heat question? Email me for an answer within 24 hrs.

 

 

mark@alliedairtexas.com

Allied Air Texas

281-355-0430

TACL B15309C

mail@alliedairtexas.com