After years of working to become debt free (other than the mortgage) and saving we bought a new HVAC unit for the house for cash. I was surprised that the unit will fit through the attic access with no holes needing to be cut. We are also getting all new R8 insulated ducts and insulating the house to R44. Hopefully gone are the days of ridiculous PGE bills as well.
That is my profession!
R8 ducting only comes in the form of flexible, it’s not the best way to duct a home, but it’s far easier and cheaper since it’s not rigid.
Long term, rigid is better, but properly installed flexible ducting is good up to 25y depending on the UV penetration of the home. Also it’s impossible to clean without tearing and rendering useless, but with changing filters on schedule and cleaning of the fan and heat exchanger or addition of hepa filter OR addition of electric filtration, the ducting should stay 85-90% dirt free.
Most furnaces can fit through a roof access in one piece, sometimes it needs separation especially if it’s a single unit sized for a hole larger than 2500sqft, either case the A coil section is separate and will be installed horizontally with a drip pan under the unit suspended and or seismic strapped due to EQs.
If the unit was sized correctly, which most HVAC residential companies don’t do correctly the unit will be about 80% efficient, they have other efficiencies that are not related to the SEER rating of the condensing unit (higher seer the better)
Cooling tonnage should be sized as a rule of thumb at 400sqft per ton, so if your home is 1800sqft you should be on a 5T condenser.
Then you can calculate your electric bill easily by BTU…
5T condenser is 60,000 BTU approx
60000/Seer rating = Wh
So you can see a lower Seer rated condenser equaling higher Wh and higher lower.
You then can look at your Wh cost on your electric bill and extrapolate your daily cost and multiply that by how many days in the month to give a rough estimate of your electric bill.
60000/18= 3333 Wh convert to kWh (/1000) is 3.3 kWh
That’s what it would be to run an hour in the summer heat.
Summer has roughly 14 heat hours, BUT!
Your AC should never be running nonstop for an hour and where I mentioned sizing comes in (most under size)
If undersized my goodness, it will cycle more often, with it only being off 15% of the time.
Let’s say your rotating energy costs are the same in Northern California with PGE as it is with SDGE and depending if they also have the tiered on peaks and off peaks and super off fuckery peaks lol. That averages about $0.40
3.3 kWh X $0.40 is $1.34h times 14 heat hours average in summer (it’s actually longer) is $18.48 a day, times 28 day cycles is is $517 a month
Higher Seer here dramatically drops said cost.
60000/24 is 2500/1000= 2.5(.40) is $1
Or $14 a day or $392
392 vs 517 or 25% less
That is giving an all day running situation so don’t freak out.
If you work outside of your home, and the house is empty, you can basically take away 10 of that 14 hours
So figure the 3.3 or $5.28 a day (4 hours) and 28 days is $147 a month
The change is how the tiered system of power is, but the math is correct based on the condenser, which doesn’t take into account the energy used by the blower of the furnace across the A coil to cool the home…
Same math can be used on the BTU rating of the furnace which for cooling is additive to the $147 a month.
Wall of text out!
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