How much generator do I need?

[rmesgt]

I want to get a generator for my home, but I don't have a clue as to how big a machine to get. How do you folks figure it out? Where do they come from? How do you wire one into your home? Do you isolate specific circuits? I am guessing that homes that use natural gas have different power requirements that full electric homes (primarily HVAC). Can military generators work for whole house systems?

 

[rcamacho]

Another MEP-802 standby generator thread

Another MEP-802 standby generator thread

Sharing progress on my project to connect a MEP-802a to the home for backup power. Infamous well nut fix. Recommend starting with this first. My genset worked great however leaked after a few weeks. Electrical panel interlock installed. This required adjusting position of all breakers a...

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[porkysplace]

I want to get a generator for my home, but I don't have a clue as to how big a machine to get. How do you folks figure it out? Where do they come from? How do you wire one into your home? Do you isolate specific circuits? I am guessing that homes that use natural gas have different power requirements that full electric homes (primarily HVAC). Can military generators work for whole house systems?

How you wired them in depends on your local building codes.

 

[Coug]

So to start with, are you trying to power your entire home, or do you only need to power certain things?
Do you have electric appliances, gas appliances, or a mix of both?
What is your primary source of heat?
Are you planning on air conditioning in the summer?

Is this strictly for the bare necessities, or do you want to live like you're still on the grid?

How big of a house, what type of location is it, how old, how well insulated, how much power do you currently use?


There are a LOT of questions that have to be answered in order to try figuring out what kind of generator you need.

If all you want to do is power the fridge, freezer, and one appliance at a time, you can get away with the MEP-802 at 5kw. This is assuming you aren't heating your whole house with electricity.

If your primary heat source is electric (be it baseboards, heat pump, electric furnace, etc) then if you want to keep the whole house warm in winter, you'll need a bigger generator.
If your primary heat is gas or wood, then you can get away with smaller.

Most of the military generators running single phase (the 120/240V in almost every house in the U.S.) are 5 or 10kw. These will NOT run an entire house unless all or most of your appliances are propane/natural gas, or you have wood heat.

If you have gas/propane appliances and a good fuel supply, then I'd recommend looking at a home standby generator instead of the military generator, as then you don't have to worry about keeping the diesel in the generator fresh if it isn't needed/used for a year or more.

As for how to power your house, with one of these 5 or 10kw, you'll either have to get a sub panel wired in that is set up for generator transfer (either automatic or manual, but most likely manual) or get an interlock installed and feed it into the main panel. Either way you're going to want an electrician involved in the process unless you really know what you are doing.
Doing a sub panel, the circuits you want to be powered get moved into the sub panel, and they are the only thing powered when the generator is running. If you do an interlock, you can pick and choose what you want to run from the panel and when, but if you aren't paying attention you can overload the generator.


These generators are awesome, but unless you regularly get outages for long periods of time, the parts supply and people to work on them are a LOT easier to find for brands like Generac, Kohler, Briggs and Stratton, and Onan (most home standby are built by these 4 brands, then many others are just a different name on them like seimens or watchdog or others)
Unless you are handy with tools, good at reading and following technical manuals, able to read parts diagrams, I'd recommend contacting a local electrician who deals with installing generators to help you figure out what you need for your situation.

 

[155mm]

I run a 804a 15kw, whole house, water well included, gas heat so less of a draw there

 

[Light in the Dark]

Tell us more about your specific homes requirements (electric appliances, including heat) and we can start to help you narrow the search. The 5kw class is perfectly sized for a typical 30A locking generator interconnect that are found on many homes. There are bigger 50 and 60A interconnects available too, at a price. The key to sizing a set is to determine how many amps you actually need.

 

[rmesgt]

So to start with, are you trying to power your entire home, or do you only need to power certain things?
Do you have electric appliances, gas appliances, or a mix of both?
What is your primary source of heat?
Are you planning on air conditioning in the summer?

Is this strictly for the bare necessities, or do you want to live like you're still on the grid?

How big of a house, what type of location is it, how old, how well insulated, how much power do you currently use?


There are a LOT of questions that have to be answered in order to try figuring out what kind of generator you need.

If all you want to do is power the fridge, freezer, and one appliance at a time, you can get away with the MEP-802 at 5kw. This is assuming you aren't heating your whole house with electricity.

If your primary heat source is electric (be it baseboards, heat pump, electric furnace, etc) then if you want to keep the whole house warm in winter, you'll need a bigger generator.
If your primary heat is gas or wood, then you can get away with smaller.

Most of the military generators running single phase (the 120/240V in almost every house in the U.S.) are 5 or 10kw. These will NOT run an entire house unless all or most of your appliances are propane/natural gas, or you have wood heat.

If you have gas/propane appliances and a good fuel supply, then I'd recommend looking at a home standby generator instead of the military generator, as then you don't have to worry about keeping the diesel in the generator fresh if it isn't needed/used for a year or more.

As for how to power your house, with one of these 5 or 10kw, you'll either have to get a sub panel wired in that is set up for generator transfer (either automatic or manual, but most likely manual) or get an interlock installed and feed it into the main panel. Either way you're going to want an electrician involved in the process unless you really know what you are doing.
Doing a sub panel, the circuits you want to be powered get moved into the sub panel, and they are the only thing powered when the generator is running. If you do an interlock, you can pick and choose what you want to run from the panel and when, but if you aren't paying attention you can overload the generator.


These generators are awesome, but unless you regularly get outages for long periods of time, the parts supply and people to work on them are a LOT easier to find for brands like Generac, Kohler, Briggs and Stratton, and Onan (most home standby are built by these 4 brands, then many others are just a different name on them like seimens or watchdog or others)
Unless you are handy with tools, good at reading and following technical manuals, able to read parts diagrams, I'd recommend contacting a local electrician who deals with installing generators to help you figure out what you need for your situation.

Thank you for your prompt reply. I was sort of leaning the way you mentioned about Generac, Kohler, etc. I will have to investigate my home to see how much power I actually draw. I am sure I could identify the primary circuits I would and determine how much energy is necessary from each circuit. I haven't yet accomplished this feat. Naturally, I would like to power my whole house, but that doesn't make much sense when comparing cost to need.

 

[Light in the Dark]

You should very easily be able to power a home with either an 802 or an 803... just a matter of defining your power needs.

Do you have electric baseboard heat? Electric appliances? Water heater? Well? Just look at the big draw items first to get you 'in the ballpark'. TVs, lights, deep freezers, computers... none of that stuff draws any real power these days.

 

[Zed254]

I've got gas heating and cooking. My 803 is too much power for my house based on recent outages. With 2 neighbors running their refrigerators and TVs off my machine through a spider box I was only pulling 30% power on the Percent Rated Current meter with 2 central AC units on in early September (hot in VA). Several weeks later during a quick outage I decided to load my machine up with electric clothes dryer and a space heater running and I maxed out at 65%.

I could get by nicely with an 802.

 

[Light in the Dark]

My 802 will literally power everything in my home simultaneously, except for my electric dryer (which is 7.7kw by itself) with a bit of capacity to go... but we have engineered our life to be able to get by with less. Gas range, electric wall oven, propane wall hung boiler for hot water and baseboards (but the wood stove does the heavy lifting in the cold months), well, 2 chest freezers, etc.

 

[bachman502]

I run a generac 25kw liquid cooled propane fueled generator. Runs the whole house. I have only electric heat. It will run the ac or heat plus the hot water heater, dryer and electric range. I wouldn’t do it any other way. Only wish natural gas was available where I live.

 

[Coug]

Thank you for your prompt reply. I was sort of leaning the way you mentioned about Generac, Kohler, etc. I will have to investigate my home to see how much power I actually draw. I am sure I could identify the primary circuits I would and determine how much energy is necessary from each circuit. I haven't yet accomplished this feat. Naturally, I would like to power my whole house, but that doesn't make much sense when comparing cost to need.

You might be surprised at the difference in cost between getting a smaller or larger generator installed.
Electricians rates tend to be rather exorbitant. You might find it is actually cheaper to get a 20 or 22kw air cooled Generac with whole house transfer installed rather than getting a smaller one and having an electrician install a transfer sub panel. The difference in the generators and transfer switches is only around $1k-$1500 between the smaller ones and the largest of the air cooled. The fuel usage is going to depend entirely on how heavily you load it up, heavily loading a smaller one will use the same amount of fuel as a lightly loaded larger one.
(and I recommend staying away from the single cylinder Generacs, the 7 or 8kw generators. Nothing really wrong with them, but I just like the redundancy of having the twin cylinder machines that can still run at half power on one cylinder).

Gaseous fueled generators (nat gas or propane) don't really care how much load you have on them, unlike the diesels, so they can sit there with minimal load for many hours without issues.

(I'm a certified Generac tech, so I lean a little more towards Generac than the other brands, but each has their strengths and weaknesses. I don't do installs, but I've done a few replacements and occasionally work with electricians or another Generac tech that does them, so I've picked up a bit)


One last thing about the Generacs, check their website to find if they have any specials going on. Last special (which might still be active) was for a free 7 year parts/labor/travel warranty instead of the standard 5 years parts and 2 years labor/travel. You have to read the details and get an in home estimate for the install to qualify, but if anything DOES go wrong it can save you thousands.

 

[csheath]

I want to get a generator for my home, but I don't have a clue as to how big a machine to get. How do you folks figure it out? Where do they come from? How do you wire one into your home? Do you isolate specific circuits? I am guessing that homes that use natural gas have different power requirements that full electric homes (primarily HVAC). Can military generators work for whole house systems?

I don't mean to offend but with that many questions I don't think you are a good candidate for a military surplus generator.

At the current trend in prices I don't think military surplus generators are a good gamble for anyone.

If you had a good mechanical and electrical apptitude and wanted to go diesel a new generator from a seller such as Hardy's might save a few bucks with minimal risk.

For most people that don't have any idea what they need the Generac brand seems to be a good path.

 

[Light in the Dark]

I think everyone has had some of those questions before they got their feet wet on these sets, so I would disagree with you here csheath. With that said, this is NOT a solution for everyone. It is entirely a DIY affair after purchase. Some have the stomach for it, others don't.

I agree that its going to be a much tougher sell going forward, especially considering the degradation in quality of whats coming across the block.

rmesgt... why are you considering this kind of power plant for your needs? Lets start here.

 

[dav5]

I don't mean to offend but with that many questions I don't think you are a good candidate for a military surplus generator.

At the current trend in prices I don't think military surplus generators are a good gamble for anyone.

If you had a good mechanical and electrical apptitude and wanted to go diesel a new generator from a seller such as Hardy's might save a few bucks with minimal risk.

For most people that don't have any idea what they need the Generac brand seems to be a good path.

I would check the reviews for Generac before I bought one. Many of the local electricians around here won't install them because of their failure rate.

 

[Coug]

I would check the reviews for Generac before I bought one. Many of the local electricians around here won't install them because of their failure rate.

What do they install then? I'm just curious from a professional standpoint

I've had more trouble with Briggs units than Generac (Briggs bought out several lines of Generac units to get their start into the home standby world)

Kohler has had a few issues in the recent past as well, their "polymer" (read: plastic) housing may not corrode, but everything inside seems to, and the housing is a pain to remove once the rivnuts in the fiberglass floor panel corrode a little and spin freely.
The big advantage to them though is they use hydraulic lifters so they don't require annual valve adjustment checks like Briggs and Generac.

Onan is nicer but just costs more.

Generac has by far the largest share of the market, and has for decades. They may seem to have a higher failure rate, but that's simply because they have the most units out there.
More than a few of the Generac generators I get first time calls for are because the electricians who installed them and get paid to service them refuse to open up the valve covers and check valve adjustment. Valves out of adjustment is probably the number one reason I get new customers.

 

[Chainbreaker]

In addition to household electrical requirements, another question is what is your budget? If your looking at a budget somewhere in the ball park of $3k-$7k your in all likelihood looking at having to essentially be your own contractor to keep it in that price range. If you elect to source a used genset yourself (Gov't surplus, Craigslist deal, etc) and pick it up and can manage the installation you can save quite a few $$$ but it requires a commitment to learn a lot of information if your not familiar with gensets & the electrical installation aspects.

If your budget is higher, then take a look at Hardy Diesel. They have some really nice Perkins, Kubotas and other generators that are "top shelf" products. However, you would still need someone to install it unless your up to the task of educating yourself on how to install something like an Interlock kit and are handy at potentially having to build a generator enclosure, assuming you don't buy one with a weatherproof enclosure.

If you just want a whole house backup generator and don't have the time or inclination for committing to a "DIY project" then you need to go with your local generator supplier and let them handle it.

 

[dav5]

What do they install then? I'm just curious from a professional standpoint

I've had more trouble with Briggs units than Generac (Briggs bought out several lines of Generac units to get their start into the home standby world)

Kohler has had a few issues in the recent past as well, their "polymer" (read: plastic) housing may not corrode, but everything inside seems to, and the housing is a pain to remove once the rivnuts in the fiberglass floor panel corrode a little and spin freely.
The big advantage to them though is they use hydraulic lifters so they don't require annual valve adjustment checks like Briggs and Generac.

Onan is nicer but just costs more.

Generac has by far the largest share of the market, and has for decades. They may seem to have a higher failure rate, but that's simply because they have the most units out there.
More than a few of the Generac generators I get first time calls for are because the electricians who installed them and get paid to service them refuse to open up the valve covers and check valve adjustment. Valves out of adjustment is probably the number one reason I get new customers.

Around here Hardy diesel mainly Yanmar and Kubota powered generators ( not sure who makes the actual generator head) are popular. It is a rural area so larger diesel generators are common. I bought my 15 hour 803A for $2000 3 years ago. I wouldn't even consider an untested military generator at the prices they are going for now

 

[rcamacho]

I was very fortunate to get an 802 in good condition but it still needed work. I would not recommend this to anyone not mechanically inclined with time to burn.


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[Coug]

Around here Hardy diesel mainly Yanmar and Kubota powered generators ( not sure who makes the actual generator head) are popular. It is a rural area so larger diesel generators are common. I bought my 15 hour 803A for $2000 3 years ago. I wouldn't even consider an untested military generator at the prices they are going for now

The Hardy Diesel generators look pretty good if you have a lot of multi-day outages on a regular basis, but cost twice as much as a comparable Generac (and that's not even counting the transfer switch). I've seen Generacs with over 4500 hours on them still running great (but then I've also helped replace some with under 100 hours on them that were falling apart from corrosion)


A 20kw Generac is $4500.
A Kubota powered 20kw is $10k or more, doesn't have any type of housing or sound attenuation, open frame.

Of the two If I knew I was going to be out of power regularly I'd go diesel. If it was an occasion outage of a few hours with a couple days outage every few years or so, then the diesel is massive overkill.