Sizing a Generator

[Zarcero]

Hey Gurus,

I would like to get a generator being that hurricane season is coming up. How do I size a generator for my needs? Do I just add up the nameplate wattages from each appliance?

I would like to be able to run two refrigerators, washer/dryer, TV, and a few other miscellaneous items.

Thanks in advance,

Mike

 

[Stuart in MN]

Many of the generator manufacturers have sizing information on their websites.

 

[rinny_tin_tin]

Hey Gurus,

I would like to get a generator being that hurricane season is coming up. How do I size a generator for my needs? Do I just add up the nameplate wattages from each appliance?

I would like to be able to run two refrigerators, washer/dryer, TV, and a few other miscellaneous items.

Thanks in advance,

Mike

You need to tally up all the loads you can reasonably expect to run at the same time and add a load growth margin. In formal terms this is called an EPLA (Electric Plant Load Analysis). For instance, you would not run an electric heater and your AC at the same time - therefore, you only need to consider the greater of the two in your aggregate sum. If you don;t have nameplate data, you can use this site to give you load demand values:

http://www.vmisales.com/voltmaster/appchart.html

- or- the NEC will likely have some values to apply.

Many of the smaller generator manufacturers do not provide other than continuous ratings, such as a 5 min, 10 min, 1/2 hour, 2hour, etc ratings to address inrush current performance - however, all these generators can provide much greater current for short term (starting) - so don;t sweat it if you run close to the continuous rating. I would add at least 20% load growth margin for a small generator, and make this sum as close to 75% of the continuous rating.

 

[sberry]

You need to skip some items, an electric dryer being one of them.

 

[Zarcero]

Thanks for the info guys. And yes, the electric dryer would be dropped off the list.

 

[rinny_tin_tin]

Thanks for the info guys. And yes, the electric dryer would be dropped off the list.

Why drop the dryer? Its has larger kw of the two (washer) and washers are frequently used with the dryer at the same time. Unless the plan is not to dry the clothes in the event of an emerg.....

 

[sberry]

Running an appliance such as a dryer or electric water heater add HUGE demand, 16 to 20 more hp required, most homes (common) could live pretty well in survival mode with a genset with 10 hp engine.

 

[Zarcero]

Why drop the dryer? Its has larger kw of the two (washer) and washers are frequently used with the dryer at the same time. Unless the plan is not to dry the clothes in the event of an emerg.....

Probably would not be drying clothes in the dryer, but putting them on a clothes line. When Ike came over our house we were without power for about a week. We would probably conserve the gasoline for the necessary running of appliances like the refrigerators, some lighting, and the washing of clothes as needed. One of the cars in the garage would serve as our fuel supply via a siphon tube to a gas can.

Who is the babe in your avatar?

 

[sberry]

A big consideration is a well, or not if on city water.

 

[ron in sc]

Depends on how you want to use it.

I brought a 3600 KW Multiquip the day after Hurricane Hugo in 1989. It still works perfectly.

I use mine by connecting it to the house 200 amp panel. This will let you use it for what you need when you need it. Of course no 220 volt stuff. I always keep the power going to the refrigerator, unless of course I want to use the dishwasher or clothes washer, then I turn off circuit to refrigerator. It takes some experimenting but basically you can run all house lights fans and other stuff with very little load.

Now it you want to run A/C unit, stoves, electric dryers and hot water heaters even one at a time you will need a seriously large generator.

I would like to have a larger unit but to get one that would run out house A/C units would be very expensive so I've so far dealt with my setup with the little generator.

 

[rinny_tin_tin]

Probably would not be drying clothes in the dryer, but putting them on a clothes line. When Ike came over our house we were without power for about a week. We would probably conserve the gasoline for the necessary running of appliances like the refrigerators, some lighting, and the washing of clothes as needed. One of the cars in the garage would serve as our fuel supply via a siphon tube to a gas can.

Who is the babe in your avatar?

Gotcha - sounds like you are thinking of a smaller unit - 5 to 10 kW,etc.
You know - the cost per kw drops significantly as you increase the size - however, endurance/fuel consumption suffer with increasing size. I'm looking at the 30 kW diesel packages sold by Trident for a whole house arrangment.

The avatar babe is my main squeeze - for my persona in the parallel bizzaro plane

 

[nate379]

When I but a gen set (need to get one) it will be large enough to run the boiler/controls, the fridge and a few lights.

If power is out, I want to keep the house from freezing and that's really the main thing.

All of the other stuff... TV, etc are extras.... hell I haven't had a TV for close to a year now.

Kill the lights and boiler for a bit and can use the washer.

 

[HOTFR8]

I found this on the Cummins website some time ago
http://www.cumminsonan.com/portable/select/ and I am sure you will find it helpfull to work out what size Gen Set you need.

 

[Mr_fixit]

8000 to 12000 watt should put you in the ballpark, narrow it down from there.

 

[nadogail]

You wil need about an honest 6 KW, 13 horse engine. You can make one for maybe $500

 

[Jeepskate]

Use the various sizing charts (they're all over the internet...I looked at several and erred on the side of caution where they disagreed), the real world numbers from the tags on your intended appliances, and take a good, hard look at what you really need/want to have if you're down for a week. I had two power outages within about 6 weeks of moving into my semi-rural house last year (first from high winds at the edge of Ike for 4 days and the second for about half a day when our tranformer blew after the substation caught on fire (at least the crews were already in the area). Fortunately my buddy had a small Generac unit that was enough to run the fridge, phone, small TV and a couple of lights. All along everyone kept telling us to expect to lose power for 3-4 days in the winter, and that these summer/fall outages were not the norm. The 'boss lady' upon hearing and experiencing this ordered me to buy a big enough generator to keep us in at least reasonable comfort, factoring in the likelihood of an outage in the winter. I ended up picking up a shipping damaged 14KW Generac Guardian standby setup off Ebay for just a touch over $2k. I run it off of a 100# LP tank (house is all electric, so NG wasn't an option). It powers both upstairs bathrooms, master bedroom, kid's room, living room, family room (has a fireplace with a blower system), kitchen essentials (light, stove, fridge...move the phone to the outlet that shares the fridge circuit), water heater, well pump, and my office (main panel and internet). We use space heaters in the winter (I'd need another 15KW+ generator just to run the heat pump and the aux heat strip) and fans in the summer. We have enough clothes to get through at least 10-14 days without laundry. We can live pretty close to normal on that setup (had one half-day outage a couple of months ago) watching TV, cooking, surfing the 'net, etc.

 

[djd99]

I have a modest unit, coleman 5500 connected to my breaker box with six breakers. My power goes out quite a bit here in Michigan and my wife requires a oxygen concentrator to breath. So far this small generator has been sufficient for our needs being our power is never out for more than 4 to 6 hours. I have my furnace on one circuit, refridge on another, and a few more rooms on the rest. So far I have not over stressed my unit as of yet and I even had to run the furnace on the last power outage. The only thing I would do over is to buy a electric start generator instead of a pull start. I found out my outfit starts great when it's warm out but when it's 20 below it's a bear to start.

 

[HOTFR8]

The only thing I would do over is to buy a electric start generator instead of a pull start. I found out my outfit starts great when it's warm out but when it's 20 below it's a bear to start.

I have been told the same thing so for the price to spend a little more it would be well worth it for peace of mind.

 

[BoydS]

Mike ...

I've lived along the coast of Texas most of my life and have been through many hurricanes (30 years South of Houston). In those 30 years of living in this area we have had only 2 major hurricanes .. Alicia 84 and Ike last year. I'll admit having a generator on hand for power outage emergencies comes in mighty handy.

There are only 2 ways to go when deciding on a genset. You either get the whole house unit or a portable unit. I see from your original post you're looking for a portable unit. There are several things to consider when selecting the portable unit. One is the size as you are concerned about. Some others are noise and fuel comsuption. Another thing to consider is how you plan to use the unit, meaning do you want to just run extension cords into the house or tie into your electrical panel (thus dedicating a few circuits to be powered).

I have a Craftsman 5600 watt portable unit (gas powered) that I've had for about 15 years. It served me well during Ike as we were without power for 6 days. This unit comes with 4-20 amp 120V circuits and 1-30 amp 220v. I was able to keep 2 refrigerators, several lights, TV (or radio), small A/C window unit and a fan. I tied into my water well as needed from the 240v circuit. We never needed the washer or dryer as everything was clean before the storm hit (something you might want to do).

Somethings I dislike about the generator I have are that it's noisy and comsumes a lot of gas. I also don't like having to run extension cords from outside into the house. Major pain as they can be tripping hazards. And if you have had any flooding in your house, you gotta keep the cords away from the wet areas. My generator burns 5 gallons of gas in 10 hrs under an 80% load. That's a lot of gas.

Other thoughts. Honda makes an excellant generator that is very quite and very fuel efficient. They also have a power conditioner that allows you to run sensitive equipment like computers and that expensive HDTV. Consider those in your shopping and stay away from the B&S engines. Make sure your generator is outside and away from windows. Electrical cords should be at least 12 ga, heavier depending on the load.

Just my 2 cents...

 

[djd99]

Mike ...

I've lived along the coast of Texas most of my life and have been through many hurricanes (30 years South of Houston). In those 30 years of living in this area we have had only 2 major hurricanes .. Alicia 84 and Ike last year. I'll admit having a generator on hand for power outage emergencies comes in mighty handy.

There are only 2 ways to go when deciding on a genset. You either get the whole house unit or a portable unit. I see from your original post you're looking for a portable unit. There are several things to consider when selecting the portable unit. One is the size as you are concerned about. Some others are noise and fuel comsuption. Another thing to consider is how you plan to use the unit, meaning do you want to just run extension cords into the house or tie into your electrical panel (thus dedicating a few circuits to be powered).

I have a Craftsman 5600 watt portable unit (gas powered) that I've had for about 15 years. It served me well during Ike as we were without power for 6 days. This unit comes with 4-20 amp 120V circuits and 1-30 amp 220v. I was able to keep 2 refrigerators, several lights, TV (or radio), small A/C window unit and a fan. I tied into my water well as needed from the 240v circuit. We never needed the washer or dryer as everything was clean before the storm hit (something you might want to do).

Somethings I dislike about the generator I have are that it's noisy and comsumes a lot of gas. I also don't like having to run extension cords from outside into the house. Major pain as they can be tripping hazards. And if you have had any flooding in your house, you gotta keep the cords away from the wet areas. My generator burns 5 gallons of gas in 10 hrs under an 80% load. That's a lot of gas.

Other thoughts. Honda makes an excellant generator that is very quite and very fuel efficient. They also have a power conditioner that allows you to run sensitive equipment like computers and that expensive HDTV. Consider those in your shopping and stay away from the B&S engines. Make sure your generator is outside and away from windows. Electrical cords should be at least 12 ga, heavier depending on the load.

Just my 2 cents...

This is why I bought the reliant manual transfer box, trust me it will be the best 300 bucks you've spent. When the power does go out, I hook up my cable from the gen to tranfers box, switch 6 breakers over and now the hole house is powered. I hated having cords run through my house.

This is the one I have...

http://www.reliancecontrols.com/ProductDisplay.aspx?R20216B

 

[Tonykarter]

Been there, done that. In the end you will tire of getting up in the middle of the night to fill the gas tank, syphon gas, find gas, store gas, change the oil in the heat of the afternoon, etc. I priced and will install a Generac 20KW standby generator when the shop is finished. Installed, with auto transfer box (with manual override), $5700. Generac has a deal for this unit that INCLUDES the transfer box, no need to buy seperately ($400).
I'll run it on natural gas with a 50lb. propane cylinder backup tee'd into the supply line just in case the natural gas goes south (it has not done so in the last three hurricanes). Uses about 1lb/hr on propane.
An inportant note: Service factor by 1.15-1.25 of total Kw demand if you are going to use natural gas. This 20Kw unit will only produce about 17Kw burning natural gas...it should only follow that others will also do the same on NG.

As I said, been there, done that...

 

[Jeepskate]

Been there, done that. In the end you will tire of getting up in the middle of the night to fill the gas tank, syphon gas, find gas, store gas, change the oil in the heat of the afternoon, etc.

That gets old *real* fast...and expensive. It's fine for a brief outage, but adds to the misery of an extended outage. What I ended up doing with the borrowed portable was gassing it up in the morning before I left for work (oh yeah...you gotta chain that puppy to something to deter theft), taking the gas cans with me and filling them up, running home at lunch to check on things and refuel if necessary, checking again after work, then staying up late to refuel before going to bed. I would at the very least look at portables that are dual or even tri-fuel capable and run on NG or LP.

I priced and will install a Generac 20KW standby generator when the shop is finished. Installed, with auto transfer box (with manual override), $5700. Generac has a deal for this unit that INCLUDES the transfer box, no need to buy seperately ($400).

I can tell you that you'll love it. Power goes out, it counts down 30 seconds in case it's just a hiccup, generator cranks over, and you're back in action. One last thing on my to do list is to put some small UPS units on my computers, satellite boxes & DVR's. When the power comes back on, it transfers back over without any interruption and goes into shutdown mode.

I'll run it on natural gas with a 50lb. propane cylinder backup tee'd into the supply line just in case the natural gas goes south (it has not done so in the last three hurricanes). Uses about 1lb/hr on propane.

FYI: You have to change a setting on the carb when you change fuel types.

Oh, quick tip: If you're installing it yourself, pull the fuses out of the transfer switch first. It uses BBUSS-5 fuses which aren't real common in the hardware store (you should buy some extras from an electrical supply store to keep on hand) and the battery charger one in particular likes to blow during the install...got that tip from an installer after I installed mine and blew the fuse.

 

[His200HerScout]

I have a 6500w Coleman Powermate portable powered by a Robin Subaru engine. I think I've used it for 30 hours total in the past 3 years.

I have a well pump, a water softener, a propane furnace, 2 fridges, and a lamp. I don't use the water heater, stove, laundry, etc.

There have been three multiple-day outages since I bought it. When in use, I keep it behind the house, out of view, so thieves don't see it (trust me -- thieves and desperados are ALWAYS on the prowl during outages, and generators are easy to spot). And I only use it a for a few hours at a time to conserve gas.

I added up the nameplates on my well pump, fridges, etc. and 6500w was plenty. The only thing I plan to do in the future is put in a manual transfer switch so I don't have to run extension cords everywhere. I enjoy candle-light when the power's out, though, so if you want your house lit up like the power never went out, go big.

Keep it maintained! You don't want to be stuck in the dark fiddling with a generator that won't start because it's full of old gas. I know -- it was 10 degrees in my garage and 36 in my house when I was fiddling with a borrowed generator that wouldn't start. I didn't throw any wrenches though

And NEVER make a suicide plug.

 

[djd99]

I have a 6500w Coleman Powermate portable powered by a Robin Subaru engine. I think I've used it for 30 hours total in the past 3 years.

I have a well pump, a water softener, a propane furnace, 2 fridges, and a lamp. I don't use the water heater, stove, laundry, etc.

There have been three multiple-day outages since I bought it. When in use, I keep it behind the house, out of view, so thieves don't see it (trust me -- thieves and desperados are ALWAYS on the prowl during outages, and generators are easy to spot). And I only use it a for a few hours at a time to conserve gas.

I added up the nameplates on my well pump, fridges, etc. and 6500w was plenty. The only thing I plan to do in the future is put in a manual transfer switch so I don't have to run extension cords everywhere. I enjoy candle-light when the power's out, though, so if you want your house lit up like the power never went out, go big.

Keep it maintained! You don't want to be stuck in the dark fiddling with a generator that won't start because it's full of old gas. I know -- it was 10 degrees in my garage and 36 in my house when I was fiddling with a borrowed generator that wouldn't start. I didn't throw any wrenches though

And NEVER make a suicide plug.

This is the same unit I own and has treated me very well and so far has been more than adequate to power my house. I chose this as I didn't have 6,000 to spend on a automatic setup.

 

[OldCarGuy]

I have a 10 KVA Cummin's Onan diesel generator set in my motor home that I can hook up to my house if there's a power failure.

I would recommend that you make a careful consideration on picking out a generator set. An 1800 RPM set is quieter and uses less fuel than a 3600 RPM unit. I personally would only consider one that is 1800 RPM. Though they are a bigger investment, a diesel unit uses far less fuel than than a natural gas, propane, or gasoline. If you're going to be using it for long periods of time this will become a major factor to consider. You'll also need to keep a large amount of fuel on hand. As deliveries may be a problem in a major outage. Normally natural gas is not shut off and may be a good way to go. Except in an earth quake or flood zone.

Particularly don't oversize a Diesel generator. Anything less than 40% usage for long periods of time can cause a condition know as 'wet stacking". A build up of carbon on the injectors. And could cause major damage.

 

[Tonykarter]

?How long are the deisel engines good before overhaul when used on a genset? That was one suprise that I had with the Generac rep came to the house. The 20KW he quoted had to be rebuilt every 2000-2250 hours, generator AND motor. That sounded a little short on lifespan to me...do the deisels have better life than that?

 

[Zarcero]

Great info guys. Thanks and keep it coming. For y'all here in Texas, I am in the Clear Lake area of Houston, near NASA.

Mike

P.S. I am having Gorrell windows installed throughout.

 

[Ira]

Not all gensets have to be derated on NG vs. LPG. Mine (Guardian 5638, now called a Generac QT022) is rated at 22kw for both. It depends on the engine. The engine used in mine is also used in the 27kw Generac (aka, Guardian), so it has plenty of power to generate 22kw on NG.

I read somewhere that Generac says the avg lifetime of an air cooled genset is 3000 hours, while the avg lifetime for a liquid cooled 1800 rpm genset is 10,000 hours. Keep in mind that the engines used in the 1800 rpm liquid cooled models are usually modified truck or auto engines. Mine has a 2.4L Mitsubishi inline four cylinder.

Mine was installed a few weeks before Ike hit. I also put in a 500 gallon LPG tank just for the genset. We lost power for four days. Had to shut down the genset once to change the oil since it was almost new, otherwise it has to be changed about every 100 hours of continuous operation. Mine runs the whole house, including A/C, water well pump, etc. Most of my other appliances are LPG if they can be. It was just like being on utility company power (except for the gallon or two of LPG it used per hour). Other than not using the electric oven, we did everything else as usual, without regard for being on generator power.

If you have UPS's for computers, they need to be good ones, preferably with an adjustable sensitivity. Cheaper ones may not like the genset power, and will switch to battery power. I have about five upper end APC units and they never complained.

Something interesting I've done since Ike is bought an energy monitor called "the energy detective" or "TED" for short. It gives you your true power usage (number of kilowatts) for the whole house on a second by second basis. You can get software with it that is pretty good. It showed me that my minimum power usage is a little less than 2kw. That's a couple of TV's, multiple lights, four dvr's, home theater system, a few ceiling fans, three computers and associated network devices and printers (not when printing), two refrigerators, etc. My 4 ton A/C takes about 4kw. My water well pump is about 2kw. So, except for the momentary surge when a motor starts up, I'm seldom using over 8kw. Microwave, toaster oven, coffee pot, blow dryer, etc. all seem to add around 2kw each.

Bottom line for me...a 22kw liquid cooled 1800 rpm genset (with a 38kw surge capacity) will handle a lot. Mine was probably running at less than 25% capacity for most of the time it was running after Ike and probably never went much over 50% capacity.

If you want to find an interesting forum for Guardian residential generators (all sizes and types), google "ziller electric". They are a Guardian dealer that sponsors a forum. Lots of good info on it. I did not buy from Ziller, but they seem to have good prices. I bought from my local Guardian dealer and had him install it. Not cheap by any standard, but I wanted someone to be there when things go wrong. He has been so far.