eepete
Platinum Member
@hr3: Great and concise fuel estimating data! tnx!
Regarding my generator size, I got it at the old house which was all electric and had two 3-ton and one 1.5 ton heat pumps. It was cheaper to buy more generator and transfer switch than it was to replace appliances. The generator cost estimate I gave was at todays cost. Back in '97 when I did this, it was $10K for a 25 KW generator (4 cylinder) and $12.5K for a 45 KW generator (6 cylinder). The resistive electric heat on the heat pumps blew everything out of the water, hence the new panel before the xfer switch. To reduce the load by 20 KW would mean all new stove, oven and hot water heater which is greater than $2.5K.
Note that this is also why I hate pricing by the kilowatt of capacity. The analogy in tractor land is comparing prices of a 48 HP tractor to a 26 HP tractor. The 48 should Not be 85% more, it would more likely be about 40-50% more. And other factors (such as transmission, frame size, tires, cab and options) are more of a factor that HP.
The 2-3X cost of generator and transfer switch is a first order estimating tool because these are two things that are easy to price. If that price passes muster, then a more detailed estimate based on pad cost, tank cost, wiring cost, labor, etc. can be done. On the packaged systems (like many of the Generacs) you can't break out the cost, but that's OK because with the generator/xfer switch priced as a package, you're down to siting cost (pad, fuel) and retrofit electrical work estimate.
New comment based on OP information: If the user is required to stagger usage, check to see if the heavy use appliances power up in the off state. If you have a power failure while some of these things are running, when the generator kicks in 10 seconds later it may see too much load. Newer appliances like stoves and ovens have electronic controls that power up off, even if it was a couple second outage. HVAC equipment want to keep on going. So in addition to getting a current draw on your appliances, make a note of how they handle a power fail and if they come back on in the same state (mechanical timers) or come back on off (electronic control). I would say that many times a year one is baking a pie, cooking a meal, drying clothes, and the HVAC is going.
Pete
Regarding my generator size, I got it at the old house which was all electric and had two 3-ton and one 1.5 ton heat pumps. It was cheaper to buy more generator and transfer switch than it was to replace appliances. The generator cost estimate I gave was at todays cost. Back in '97 when I did this, it was $10K for a 25 KW generator (4 cylinder) and $12.5K for a 45 KW generator (6 cylinder). The resistive electric heat on the heat pumps blew everything out of the water, hence the new panel before the xfer switch. To reduce the load by 20 KW would mean all new stove, oven and hot water heater which is greater than $2.5K.
Note that this is also why I hate pricing by the kilowatt of capacity. The analogy in tractor land is comparing prices of a 48 HP tractor to a 26 HP tractor. The 48 should Not be 85% more, it would more likely be about 40-50% more. And other factors (such as transmission, frame size, tires, cab and options) are more of a factor that HP.
The 2-3X cost of generator and transfer switch is a first order estimating tool because these are two things that are easy to price. If that price passes muster, then a more detailed estimate based on pad cost, tank cost, wiring cost, labor, etc. can be done. On the packaged systems (like many of the Generacs) you can't break out the cost, but that's OK because with the generator/xfer switch priced as a package, you're down to siting cost (pad, fuel) and retrofit electrical work estimate.
New comment based on OP information: If the user is required to stagger usage, check to see if the heavy use appliances power up in the off state. If you have a power failure while some of these things are running, when the generator kicks in 10 seconds later it may see too much load. Newer appliances like stoves and ovens have electronic controls that power up off, even if it was a couple second outage. HVAC equipment want to keep on going. So in addition to getting a current draw on your appliances, make a note of how they handle a power fail and if they come back on in the same state (mechanical timers) or come back on off (electronic control). I would say that many times a year one is baking a pie, cooking a meal, drying clothes, and the HVAC is going.
Pete
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