Originally Posted By: Robert L Dean This post was automatically imported from our archived forum.
Most air conditioning manufacturers make it possible to identify what the tonnage is with the model number of the unit alone.Some use the indoor and some use the outdoor unit.The way to tell is simple.The tonnage goes in increments of 6. For instance ESQ-018.The 018 is a 1 1/2 ton. This is the lowest tonnage. Next is ESQ-024. The 024 is a 2 ton. Next is ESQ-030.
The 030 is 2 1/2 ton.Next is ESQ-036. the 036 is a 3 ton.Next is ESQ-042.The 042 is a 3 1/2 ton. Next is 048 for a 4 ton. Then there is no such thing as a 4 1/2 ton. And finally 060 for a 5 ton. A 5 ton is the largest of the residential units.
This is the most common for residential air conditioning. Some manufacturers do not use this system.Like Rheem for instance.You must have the literature for these. The ESQ I used above is not an actual model number, but just an example.
Originally Posted By: Robert L Dean This post was automatically imported from our archived forum.
bdowd wrote:
Do you have a way to figure out what the correct tonnage should be based on square footage? If so what is the formula?
Thank You Bruce A. Dowd A & A Home Inspections
There are several formulas relating to Thermodynamics,and refrigeration. One in particular is related to CFM's multiplied by tonnage. I think that is more information than the average home inspector really needs.I was simply trying to give an easy to use visual method of finding an Systems tonnage. Sincerely
Originally Posted By: mrose This post was automatically imported from our archived forum.
Greetings,
If your interest in AC tonnage is derive from the client's question of whether the system is" big enough" to cool the house be careful on how you answer.
In Georgia the design temperature for sizing equipment is based on approximately 92 degree F. outside dry bulb ambient temperature. A rule of thumb, or any other digit you may choose, suggests that a correctly sized system with reduce the inside temperature 14 - 16 degrees lower than the outside temperature.
Here's the catch. Does the occupant want the inside temperature 68 degrees or 78 degrees to achieve adequate comfort. Some want it cold enough to hang meat.
In reality the heating contractor performs an engineering load calculation from a " manual J" set of tables. In short many design factors of the structure effect the heat transfer. ( glass area, insulation, directional considerations and many others)
Keep in mind that a key element of achievingi nside comfort design is proper airflow. If you can't get the air in and out of a room the size of equipment become a moot point.
Thanks for listening to me dump my bucket.
A wise man once said"old AC servicemen never die; they just loose their charge".
Best regards,
-- Mike Rose
Cornerstone Home Inspection Co. LLC
Lawrenceville, GA
Originally Posted By: rsummers This post was automatically imported from our archived forum.
mrose wrote:
Greetings,
If your interest in AC tonnage is derive from the client's question of whether the system is" big enough" to cool the house be careful on how you answer.
In Georgia the design temperature for sizing equipment is based on approximately 92 degree F. outside dry bulb ambient temperature. A rule of thumb, or any other digit you may choose, suggests that a correctly sized system with reduce the inside temperature 14 - 16 degrees lower than the outside temperature.
Here's the catch. Does the occupant want the inside temperature 68 degrees or 78 degrees to achieve adequate comfort. Some want it cold enough to hang meat.
In reality the heating contractor performs an engineering load calculation from a " manual J" set of tables. In short many design factors of the structure effect the heat transfer. ( glass area, insulation, directional considerations and many others)
Keep in mind that a key element of achievingi nside comfort design is proper airflow. If you can't get the air in and out of a room the size of equipment become a moot point.
Thanks for listening to me dump my bucket.
A wise man once said"old AC servicemen never die; they just loose their charge".
Originally Posted By: roconnor This post was automatically imported from our archived forum.
The 500 sf to 600 sf per ton rule of thumb also seems to work as a rough check here on east coast. 550 sf/ton for average conditions, and then adjust up or down as needed for actual conditions (insulation, glass area, ceiling height, etc.).
A brother and several other HVAC contractors I know all do detailed load calcs for sizing the systems, and then as a reality check use the rules of thumb. So I think its a pretty good guide for a HI .
I understand that AC [compressors] should be properly sized, or actually slightly undersized ... but not oversized. This is one case where more is not better. Really oversized systems don't work that great since the compressor cycles on and off too much, which not only causes more wear but also doesn't cool as effectively since the systems doesnt get a chance to remove a lot of moisture from the air (a big part of cooling).
Another rule of thumb I have heard as a reality check on the compressor nameplate rating is 7 Amps (FLA) per Ton (12,000 BTU) of cooling.
-- Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee
I am absolutely amazed sometimes by how much thought goes into doing things wrong
Originally Posted By: johlstrom This post was automatically imported from our archived forum.
The way to increase efficiency is to increase the coil size. This gives you more surface area to transfer heat. However, I have seen where the condenser coil has been replaced to a 12 SEER and the evaporator is left alone. If the evaporator is only a 10 SEER, you will only get the efficiency of a 10 SEER unit. Home owners do this because they cant afford the indoor coil to be replaced at the same time as the outdoor coil. Something you might want to watch out for when telling the buyer that the unit is a higher efficiency
Originally Posted By: johlstrom This post was automatically imported from our archived forum.
I agree with Rolland, the seer rating increase is only about 10%, if that. I used to install A/C units and most homeowners wont increase the SEER rating if they are leaving the house in 5 years or less. It just doesn’t pay for itself over that short of a time. (Of course, most companies wont tell the homeowner that info) As far as getting the bigger A-coil to increase efficiency, you would need both indoor and outdoor units replaced to increase it.
Originally Posted By: Blaine Wiley This post was automatically imported from our archived forum.
Hows things in Centreville, James. I used to inspect right next door to you in Sterling.
Here's some anecdotal evidence. My next door neighbor and I replaced our heat pumps around the same time in 2001. He went with the Trane 14 SEER model (3? tons) and I went with the same size 10 SEER model. He had the beautiful two speed motor, and all of the bells and whistles. Mine was just the standard model. Our houses were within 100 square feet in size, at that time I had two small kids, he had a teenager. We both kept our heat setting at 67 and our AC setting at 73.
His electric bill was never more than $20 less than mine. He paid about $4600 for his system, and I paid $3300 for mine. That's a whole lotta months of operation to break even. 
Originally Posted By: johlstrom This post was automatically imported from our archived forum.
Things are getting cold up here Blaine. I just left Key West a few weeks ago. What a great time! That is exactly what I am talking about. The increased SEER will pay for itself over time, A LOT OF TIME!
