Alright here's the question:
I've got a
2800 sq ft house 3 bdr
built in 2005
below ground basement
open floor plan/high ceilings
One stage furnace
I have heard that I could get a 4 ton 13 seer unit with a 5 ton coil
(trane) or go with a 5 ton 13 seer(rheem) with a 5 ton coil.
Will I get better efficiency with the 4 ton/5 ton coil trane?
Way confused! Thanks
If you have a 4 ton unit, then you only get 4 tons of cooling.
If you have a 5 ton unit, then you get 5 tons of cooling (more
Both units are rated 13 SEER, so the efficiency should be the same as
far as energy efficiency is concerned.
Why put a greater capacity coil on a smaller unit? Who recommended
As far as design is concerned - how much A/C is actually needed for
I assume that this is the only unit.
What unit and capacity are you replacing, since it was built last year.
First you need a heat gain calculation to tell you how many tons (BTUs)
of cooling you need. It sounds like your contractor(s) is/are guessing.
Once you know the BTU load then the contractor will assist you in
selecting the right size condensor and coil. It is not uncommon to
slightly oversize the coil to get somewhat better efficiency (SEER).
However, you want to be sure that the sensible and latent heat
requirements of the load are met.
Why in the world do you think they put these labels on them, 3 ton 4
ton, 5 ton etc?????
It is so the proper sized equipment outside gets matched up with the
proper size equipment outside.
With a 2005 built house, why in the world are you considering a HVAC
change after only one year????
5 ton compressor/condenser should always be matched with 5 ton
coil/evaporator. Any money you save on purchase costs is likely to be
eaten up by operating costs, and in fact, it may cost you more to
operate as the 4 ton compressor will work harder/longer to cool the
house in summertime.
The only way to know for certain, however, is to have a reputable HVAC
contractor come out, inspect the system and make recommendations.
Virtually all manufacturers have certified upsized coils for use with
Evaaporator coil size is a major factor in determining the balance
between sensible and latent heat removal. Larger evaporator coils
normally remove less humidity, because they operate at a higher coil
temperature/pressure ratio --smaller evaporator coils tend to
remove more humidity --because they normally operate at a lower
operating temperature. The SEER is usually slightly higher with larger
See ARI Primenet for specific ratings.
So in Denver with relatively lower humidity than Gulf Coast locations, a
larger coil MAY be a recommended practice.
Here in Houston, or New Orleans, or Pensacola, or Mobile... humidity
extraction is a big concern as the number of 90+/90+ days is very high.
In these locations a 5 ton coil should be matched with a 5 ton compressor.
Denver, CO summer design conditions: 91 dry bulb 59 wet bulb!
Approximately 12 to 13% Relative Humidity.
You shouldn't have a latent load which frees up the sensible capacity
handle the sensible temperature load.
In a ultra dry climate, go for an oversized evaporator coil, TXV, and
450-cfm of airflow per ton of cooling.
I hope your supply and return air is at or near the ceiling for the
cooling mode and near the floor for heating.
This will optimize the temperature differentials of the air and the heat
which transfers more heat from a specific amount of a cubic foot of
airflow. (More efficient operation)
Have a competent/trustworthy heat gain calc done, then do more to reduce
the heat-gain and size the equipment accordingly.
I would think you could get the sensible heatload and condenser sizing
down to at least 3.5-ton with a matched 4-ton evaporator coil.
Save needless expenses.
Air Conditioning\'s Affordable Path to the "Human Comfort Zone Goal"
Thanks for the info....just from the above responses, you can see how
much of a "Science" HVAC systems are if done right!!! I now understand
that an installer needs to do the calculations and take the right time
doing it. Thanks again!
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