So, if my highest draw during the last winter was 2.0KW in January and my total draw between October and March 31 was 9.5KW, how big a generator do I need?

House is 2700 sq feet, we have two 40gal Water heaters, one furnace A/C, a stove/cooktop, 3 fridges and two freezers, and a hot tub.

I'm waiting for a quote from a nationally advertised vendor, but I'm pretty sure he's going to try and sell me a 18-22KW unit which seems a little over the top, especially as our last house was 3800 square feet with all the same stuff, plus 3 IKW baseboard heaters and another furnace/AC unit but minus the hot tub; and that place only needed a 16KW unit.

Generators are like ammo- in very short supply. Demand has outpaced production.
You will be able to get a quote, they may only have 20 kw in stock.

quote:

Originally posted by SIGfourme:
Generators are like ammo- in very short supply. Demand has outpaced production.
You will be able to get a quote, they may only have 20 kw in stock.

Yeah, I know, but that wasn't my question.

When the time came for me to purchase a Generator, I was looking for something large enough to run my Well and a few other essentials only. I was not looking for one large enough to run everything I desire at once. That would be a luxury I didn't need.

I ended up buying two Generators. A Honda EM5000sx and Honda 2200-Watt 120V Inverter.



https://www.acmetools.com/shop...s/honda-em5000sxk3an

https://www.acmetools.com/shop/tools/honda-eu2200ig

I feel I have the best combination for my needs.

Are you looking for emergency power or daily use power?

If the former, you need a circuit for just the essentials (fridges, water, heat, etc and only have those items on that circuit.

If a daily use generator, you'll need a larger generator. Could run through the math for you but, there are unknowns which an on-site inspection may need (condition of wires, current circuits (no pun intended) for use, etc.

I'm looking for a unit to run my whole house for a limited period during an outage, maybe up to a week. I know I'll need a auto transfer switch, like I had at my last house. I forgot to add, the new place has a well pump, which the old one didn't. The gen will run from a 1000 gal LP tanks.

How many of those do you plan on running at the same time because that's what'll determine the size of the generator you need. It will have nothing to do with how many kWh you use each month.

Both water heaters, your hot tub, and the oven get you up to 18kW.

Plug in your numbers.....

https://www.norwall.com/power-...rt/power-calculator/

quote:

Originally posted by Jupiter:
When the time came for me to purchase a Generator, I was looking for something large enough to run my Well and a few other essentials only. I was not looking for one large enough to run everything I desire at once. That would be a luxury I didn't need.

That was my thinking and that's what I did. Our backup generator supplies:

• Well
  
• Sump pump
  
• Furnace (not A/C, though)
  
• Refrigerator
  
• Freezer
  
• Alarm system
  
• Video surveillance system
  
• LAN server and associated network gear, incl. CM and WiFi
  
• Entertainment system
  

Generator consumes 1/3 gal/hr. at half load.

Ran into a bit of a problem when we upgraded the well because I'd sized the generator for the old 2 in. well. The new well, with it's 18 GPM, 1 HP, 240VAC motor was a serious start-up drag. That got fixed when we upgraded the well to a VFD motor. Because of the soft start you can't even tell when the pump fires up.

quote:

Originally posted by Pyker:
I'm looking for a unit to run my whole house for a limited period during an outage, maybe up to a week. I know I'll need a auto transfer switch, like I had at my last house. I forgot to add, the new place has a well pump, which the old one didn't. The gen will run from a 1000 gal LP tanks.

Have been looking at whole house standby gens for the last few weeks. 22kw seems to be about right for a house having a heat pump and no gas appliances. However, when you consider running on propane, it becomes outrageously expensive to produce electricity 24/7. At about $4 a gallon, your 1000 gal. tank (really only 800 gals) will cost you $3200 to fill it and you'll use most of it on a two week outage. If I had access to natural gas, a whole house gen would be a good choice. As for now, a 10kw electric start gasoline/propane and a manual transfer switch will work for me.

quote:

Originally posted by Pyker:
the new place has a well pump

You'll want to know more about the well pump motor - those can draw a boatload of amps and need to be factored into the mix when figuring your peak demand.

If it's old, you may find you want to replace it with something with a smoother startup.

16kw Generac in my 1700 sq ft home, natural gas

This message has been edited. Last edited by: wxl,

quote:

Originally posted by Pyker:
we have two 40gal Water heaters, one furnace A/C, a stove/cooktop, 3 fridges and two freezers, and a hot tub.

Not near enough info for anyone to make a guesstimate.

Water heaters: atmospheric vented gas, power vented gas, electric or possibly tankless?
Furnace: specifications needed.
A/C: specifications needed.
Stove/cooktop: again specs, gas/electric?
Hot tub: can have a wide range of power requirements depending on specifics.
Well pump: specs needed.

How about the washer, dryer (electric/gas), microwave, other high electrical drawing cooking appliances.

quote:

Originally posted by Pyker:
I'm waiting for a quote from a nationally advertised vendor.

Normally, the quickest way to get the highest cost for mediocre workmanship.

Find the best local electrician and have a chat to see what they recommend. Find one which will properly size the unit, install said unit and perform the require upkeep and maintenance.

I have a 9500w generator (manual) that I use an interlock to backfeed my panel for whole-house power.

I understand I am limited in what I can use:
- I can run the toaster oven and one large stove element, I cannot run my oven.
- I can run the furnace, well pump, refrigerator and freezers, but not the electric Hot Water Tank.
- I can run the Hot water tank, well pump, bathroom fans, but not with the freezers, or any kitchen appliances.
- My generator is not a fan of my microwave, so that stays off.

My generator runs most "normal" usage at under a 25% load, the Hot Water and Well pump usage is probably the most taxing at around 50-75% load.

If I were going to a whole-house automatic stand-by generator, I would go 17.5kw minimum for my needs, So that I wouldn't have to worry about load limits.

My usage isn't yours however, just sharing my experience.

quote:

Originally posted by SIGfourme:
Plug in your numbers.....

https://www.norwall.com/power-...rt/power-calculator/

or Generac does the same

https://www.generac.com/for-ho...build-your-generator


Basically you should look at what draws the most power, electric dryers, electric cook top and oven, pool pump, water heaters, they all run 220, eliminate much of those and you reduce the electric needs.

We have LP water heater so all it needs is a little 110 tickle to turn it on, same for the cooktop. When the dryer goes out I'll convert it to LP.

My experience was it wasnt as much the cost of the generator, but also switch and fuel tank - but the labor. Shit, these electricians must make more than surgeons!

If you intend to run your whole list at the same time a 22kw generator will be too small. We have an LP furnace, an LP water heater, an LP stove, a well pump, no hot tub (6000 watts)and would never run AC during a power outage and we get by with a 12kw generator. If you are trying to save bucks you are going to have to give up some comforts you enjoy when the regular power is operating. You don't specify what your furnace is.

The other thing you have to consider is fuel usage.

I couldn't recall the numbers, so I did a search. Found this: The Relative Efficiency of Gasoline, Natural Gas, and Propane Fuels For Back-Up Generators

The generator he's citing for an example can't be much bigger than our 4kw/5kw generator, being as he's citing 0.42 gal/hr for gasoline, and ours is 0.33 gal/hr at half load. A 22kw or larger generator would consume significantly more fuel, obviously.

I'm going to make a statement about something I am not familiar enough with, but I know enough about to make myself look the fool.

Although KW rating is nice, I would look more at your amp draw and the available AMPs from the genset. I quick look at a Kohler 24kw generator shows it is only rated for 100a on NG and 87a on LP.

I learned the AMP lesson the hard way. I have a Kohler 14kw genset that is rated for 58a on LP. But at 6200 feet, if I try to pull more than 32a, it overspeeds and faults out. 58a should have been plenty as a backup for my solar after 3 cloudy days. Luckily even 30a works for my system and I can get a full recharge in 3.7hrs from this genset. The company that designed my system and specced the components with a lot of excess robustness because I asked them to!

As a side note, my genset never delivers power directly to the AC panel unless I fire it up and lock out AC inverted power from the batteries to do some other maintenance. My charge controllers/DC management is set so that it never asks for more than 30a.

So If you have a 200a panel but your genset can only deliver 100a, what is the equation? I think this is more the answer you need to figure out.

quote:

Originally posted by ensigmatic:
The other thing you have to consider is fuel usage.

I couldn't recall the numbers, so I did a search. Found this: The Relative Efficiency of Gasoline, Natural Gas, and Propane Fuels For Back-Up Generators

The generator he's citing for an example can't be much bigger than our 4kw/5kw generator, being as he's citing 0.42 gal/hr for gasoline, and ours is 0.33 gal/hr at half load. A 22kw or larger generator would consume significantly more fuel, obviously.

Fuel Consumption was a big consideration for me. Running a large generator for long periods of time can get expensive.
Our smaller honda-eu2200ig can run for hours on a gallon of gas. We only run the larger EM5000 when needed.
I love having the portable unit for other tasks.