Help me pick a generator size

Joined
Sep 30, 2013
Messages
16,185
Location
Indiana
Happy Friday BITOG.

For power outages, I'd like to run the water pump, a few lights, the furnace (if needed), a fridge and freezer. The idea of being able to run everything at once sounds nice, but it isn't necessary either. My concern is excessive fuel consumption by getting a larger model that can run everything. I'm thinking something around 7kw. Unsure of fuel type, but will likely just get a model from HF for now.

What's everyone's thoughts?
 
I went with a 6500 watt generator for my needs which are similar to your needs. Worked fine when I used it for power outages. I just flip the breakers on in sequence for the appliances and the generator handles it all fine.
 
Yes, something around 7,500 watts output. Not starting watts. I have a 5,500 and wish I had a size larger.
 
Last edited:
You'll have to have some headroom to account for startup surge when the pump, compressors, or fan kick in. Is your pump 240V? I've comfortably run lighting, furnace, and the refrigerator from a Predator 4000. A well pump and a separate freezer might be pushing it, assuming a well pump is around 1HP.

Don't forget to run it periodically with a load, and keep stabilizer in the tank. Lack of use and stale gas is no good for them.
 
my mom & dad survived a week long outage post a big ice storm back in '04 with a 5kw. running similar load to what you're proposing. adding in the sump pump that cycles regularly (
few years later he had an automatic whole house unit put in. generac 18kw (it would be 20kw on propane, only 18kw on natural gas )had it wired up to run everything except the central air...

since it's gone in, the longest outage has been about an hour. usually the power is out JUST long enough for the genny to fire up..
 
Last edited:
Be careful what you run on a typical non invertor portable generator.. Electronics in a modern furnace are not something I'd hook up to an old fashioned generator. Lots of people in Clintonville, OH lost their power for a week, bought or had a cheap generator to run the fridge which the fridge broke down due to dirty power.there an article on it somewhere.
 
Yep , add up all the loads you expect to use then add in a start up factor for motor load ( especially a central A/C system ) . Do not short change yourself .

Keep in mind adequate fuel storage for an extended outage . Also , I suggest you run it under load once or twice a month .

A back up generator system is not a simple , easy or cheap system .

Best of luck to you .
 
Originally Posted by WyrTwister
Yep , add up all the loads you expect to use then add in a start up factor for motor load ( especially a central A/C system ) . Do not short change yourself .

Keep in mind adequate fuel storage for an extended outage . Also , I suggest you run it under load once or twice a month .

A back up generator system is not a simple , easy or cheap system .

Best of luck to you .


This!!! I got quite the lesson when I put in a 16k Generac propane.
 
The problem to me when you go into the ~7KW+ range with a portable gasoline powered unit is you are going to burn in excess of a gallon per hour if the generator has a load on it.

Will you have that amount of fuel on hand? Will you be able to source it during an outage?

I get it that you need it if you have to run well pumps, a/c, etc, but to me, for a roll-around portable unit, it's all about being able to minimize during an outage. I'd rather have 2-3 small units, with some or all being inverter units.
 
A 5500W generator (340cc engine) (remember that some generators are improperly rated) is the minimum size to start a typical well pump. A 5500W unit will start a 2HP shallow well pump, or a 1HP deep well pump, as long as other loads are minimized.

You might see some generators rated at 5000 or 5500 watts with 270cc engines. These are not capable of starting large motors.

I always recommend looking carefully at the engine size. 340cc engines are a minimum size for success. Generator heads hover around 90% efficient, so there is no magic there. Overhead valve engine output is very closely tied to displacement.
 
Have a 5kw Coleman/Tecumseh since the mid 90s. Similar loads to the op's. Runs all the listed items fine, except a water pump. Actually a basement sump pump. Was running my generator during an outage and my neighbor asked if he could plug his fridge in via a long extension. It was fine but then my generator starts surging heavily. Find out the neighbor plugged a sump pump into the extension cord. The surging was due to the start up load of the pump.

The worst case of needing my generator was a week in December when the power was off for nearly a week. Temps were below freezing as usual up here. The computers in the gas furnace and gas hot water systems ran fine.
 
Originally Posted by dlundblad
Happy Friday BITOG.

For power outages, I'd like to run the water pump, a few lights, the furnace (if needed), a fridge and freezer. The idea of being able to run everything at once sounds nice, but it isn't necessary either. My concern is excessive fuel consumption by getting a larger model that can run everything. I'm thinking something around 7kw. Unsure of fuel type, but will likely just get a model from HF for now.

What's everyone's thoughts?



For both fuel consumption and sanity reasons you probably want to look at an inverter genset that varies RPM based on load vs a fixed speed 3600RPM genset.

The yamaha 6300 inverter is great value and it will last a lifetime, and you can get parts for it at a motorcycle shop.

The Honda 7K is also pretty awesome, has great parts availability - but it is super expensive.

The predators champions and others are cheap, and can givee good service and life, but typically have FAR fewer valve lash inspection intervals and are much harder to get parts for.

UD
 
I have a 20Kw B&S that runs on propane. Self starting, self shut down, self tests every month. Runs everything - well pump and a booster pump, hot tub, 3 refrigerators, 1 electric water heater, 2 electric dryers, 1 electric range top, 4 electric ovens, etc. (Caveat - I haven't intentionally turned everything on at the same time to test, but in the 5 years we've had it there has been no problems with an overload.) I don't have AC or a pool.
Really nice unit and we like it a lot, but..... it goes through 2.3 gals of propane per hour at 50% load and 3.7 gals at full load. (I paid $3 a gallon for my last fill-up Feb 1, but I'm in California so pretty sure I'm getting screwed! lol...) Anyway, at my rate that works out to almost $7 an hour at 50% up to $11 an hour at full load. With the wildfire outages we have here (basically they turn the power off when the wind blows hard), an outage can last for a few hours to a few days!
 
I have a 5500 with a 7500w surge. It will run my furnace or AC , sump pumps, fridge and entertainment things. All off extension cords, I don't want to put the money in for a whole house interchange. You can get individual transfer boxes for the furnace that will allow you to run the furnace off of the extension cord.

The critical thing for me is running the sump pump. We had a lot of power outages in July, luckily July was probably the only dry month we had last year. I NEED to run the sump pump in the crawlspace otherwise the house will flood right up to the floor joists.

Since it's so rarely used, I syphon the gas out and run it in my jeep. I have 5 gallons of ethanol free gas ready to go in it (or any other OPE). If it gets old it will get put in the Jeep and I'll buy new. If we have a really extended power outage, I have 35 gallons in the truck and 20 in the jeep and synthetic 20w50 for the generator for extended usage.
 
Originally Posted by UncleDave
Originally Posted by dlundblad
Happy Friday BITOG.

For power outages, I'd like to run the water pump, a few lights, the furnace (if needed), a fridge and freezer. The idea of being able to run everything at once sounds nice, but it isn't necessary either. My concern is excessive fuel consumption by getting a larger model that can run everything. I'm thinking something around 7kw. Unsure of fuel type, but will likely just get a model from HF for now.

What's everyone's thoughts?



Sorry - bad phrasing -

The predators champions and others are cheap, and can give good service and life, but typically have FAR fewer hours between valve lash inspection intervals and are much harder to get parts for.

UD
 
Gensets are most efficient @ 80% capacity. Given what you want to run and if it were me, I would buy a 10k starting and around 8500 constant running. With that, you can comfortably run what you brung and not burn through fuel or over work the genset. In this situation, its almost always best to think bigger is better.
 
IF I had natural gas at my home, there is no doubt that I would have a Generac whole house standby unit. The price, roughly $3000.00 without installation sounds extremely low to me. Particularly when you consider the fact that Honda portables can exceed $2700.00 easily, then you need large amounts of fuel stored. You can even step down in size and get a unit for $2200.00 that will handle everything you mention.

Just NO comparison.

As always, there are plenty of resources on generator sizing available on the web. Even Honda's website will help you out if you wish.
 
I bought a used diesel Multiquip 12KW Whisperwatt with new motor all service and records.

I have a manual transfer switch and can run everything we need including our well pump.

It's quiet and just runs and runs as long as there is fuel.
And that is the tradeoff: capacity vs fuel burn.
With diesel, you need to load it (size it) so it is not underutilized.

I wanted something a little more substantial/industrial grade rather than the homeowner grade stuff since we live on acreage out in the sticks.

True, you need to run/load this stuff at least monthly.
I put a big load on this, usually dryer and space heaters together once as month.

Might be a hassle to some, but that's life...when you live rural.

Anyway, this is another way of approaching the generator need.
 
I have a Champion 3500. It can run my fridge, upright freezer, 2 satellite receivers, 2 flat screens, a satellite internet modem and several lamps... EASILY. The 4 gallon tank lasts 8+ hours on that load. Then I shut down, refuel and switch over to 220v long enough to refill my well tank. Every now and then I wish I had generator big enough to run the water heater, but even though I live in hurricane country, I just don't lose power that often.
 
Originally Posted by JTK
The problem to me when you go into the ~7KW+ range with a portable gasoline powered unit is you are going to burn in excess of a gallon per hour if the generator has a load on it.

Will you have that amount of fuel on hand? Will you be able to source it during an outage?

I get it that you need it if you have to run well pumps, a/c, etc, but to me, for a roll-around portable unit, it's all about being able to minimize during an outage. I'd rather have 2-3 small units, with some or all being inverter units.


I've got a 7500watt continuous/9500watt startup and when power outage is a possibility I have 6 gallons in it's tank, two additional 5 gallon cans and in the event of a long outage a 38 gallon tank in the Tundra and another 16 gallons in the RX350 for a grand total of 68 gallons of fuel. . My point...as long as you can syphon gas from vehicles they can be a great backup for the generator. That will give me close to 30 hours at full output and double that more normal outputs.

Now my in-laws propane powered Generac will do a solid week on a tank of propane but it's was also 20x the cost.....
 
Back
Top