What I have heard or read but not from experience.
Onan Very good brand
Generac - many generac specific parts that can be hard to obtain if you are not a dealer

Without specifics of your situation, it is not possible to make a detailed recommendation. The "big three" in the commercial standby power business are Cummins/Onan, Kohler, and Caterpillar (Guardian). The earlier Generac units are a nightmare to install and work on, rumor has that later ones are somewhat better. Parts are expensive for just about any brand, for example I ordered a 3 amp battery charger yesterday, it was right at $225 from Cummins.

i have heard not to get a kohler...is there a reason why?

A Kohler is probably as good as any in the price range you are considering. All of the major players have produced a model or two in the past that turned out to be less than ideal. Having said that, they are industry leaders for a reason.

Hi,

I am not sure where in the USA you live hence am not sure of your circumstances. From what I can see you are looking at Mid-range generators for back up power for a whole house. Rather than petrol / portable ones.

Mid-Range generators are usually powered by Natural gas if you have a mains supply, or by propane stored in a large tank.

I have a Cummins Onan RS20000 bought about 2 years ago now. This is a Ford car engine based generator. The newer version is a GM car engine based generator. I bought it from Costco for $US 9000 including the ATS (Automatic Transfer Switch). They cost about $US 15,000 now I think. Copper is more expensive.

Note putting in one of these Generators can be quite a big job. If you need the larger ones, you are looking at heavy lift equipment, a back-hoe or a crane. If you stick with the 15 kw or below, these are usually lawn mower engine based and a unit can be carried by 4 men.

You mentioned Air Conditioning in your post. Generators will run air conditioning units IF you get a generator big enough. Whole house Air conditioning uses alot of power. My 20,000 kw will run the 1.5 tonne unit, however I was advised not to connect up the 2 tonne unit. Smaller generators (15 KW) will run quite easily however the smaller all on one through the window based units. Some people in Florida have a small A/C window based unit just for emergencies. Then they make one room the A/C room. They do not try and run the whole house A/C off the generator.

Getting one within a week is quite a rushed time frame. My installation took 4 months, and included local inspectors etc.

If you are looking for a brand I think Cummins Onan provided good service. When the unit arrive from Costco it was missing a hinge pin. Getting a replacement part out of Costco was difficult. Customer service is more used to pots and pan returns. However once through to Cummins Onan that was a differnet story. The Cummins Onan link to costco is via Cummins Onan Western Region. Those guys liasied well with the Cummins Onan North East out of New York (where I am). An engineer came out to look at the generator sitting in my drive way. Came back a few days later with the parts. Two visits no charge. I paid $US 600 for them to come and turn it on and check it out. They tuned it, and had it running stable. The guy was there like 4 hours and very professional. They also came back again after a recall notice to update some gas valve software. Again free of charge.

At work we have Cummins Onan power generators as backup. These guys are the size of a 18-wheel trucks. The same guys who service these also do the residential service. They may cost more, but I think they are very good.

So far my Cummins Onan has had zero issues and over two years I have run it about 11 hours. The Ford engine is a standard Ranger car engine with a propane converter. Parts are available at any Ford car dealer. I changed the oil myself which is easy.

As for what you want to run. Most peoples order of priorities are usually sligtly differrent to yours. You may or may hot have these.

1) Sump pump
2) Well
3) Furnace fan
4) Furnace electronics
5) Air handlers for heating / HVAC electronics
6) Fridge / Freezers
7) Lights
8) Air conditioning.

Good luck with your installation.

All the best, Mike.

I have the Generac 15KW air cooled unit. Bought it 2.5years ago through Amazon for just shy of $3000 including the ATS and a 12 circuit load panel, controls, battery charger and preformed base. Install took about 4 days of work on my behalf and then had a licenced gas fitter install the new 3/4" NG line.

Works very well and has been very reliable. Only parts I have needed so far have been oil filters. They are available from NAPA or Home Depot.

The unit has no difficulty running BOTH of our central AC units. One 4 ton and one 3 ton. Both very high efficiency units which helps a good deal. Also powers all lights and most other 120v circuits in the house. No other 220v loads.

Except for the gas plumbing, I did all the installation myself and passed inspections first try.

This is what i have been looking for. I am planning to run one or two smaller AC units. The entire house has 4 units, but they are smaller ones with 4 different zones. I am really hearing great stuff out of Onan and Generac, but the Onan dealer will not give me the time of day. I hate to base my purchase on this, but if you cant call someone back...how certain can i be about the after the sale service?
MS

Unfortunately, homeowners are not the primary market for most Cummins/Onan dealers. Your request for service will be done by the same technicians as those of commercial customers, some of which pay nearly as much as your set will cost for an oil change and routine service. The salesman you leave a message for deals with customers every day who may buy a half dozen large gensets per year. Whose call would you return first?

you might check out a web site norwall.com. They sell generators - Onan, Kohler, and Generac as well as a few others. I have not purchased from them yet but am planning to.

I have been in the hunt for a generator system too. I have learned a lot fom the GW as well as talking to different vendors. One thing I just learned is that while Kohler is a very good brand - it was rtecommended to me to not buy the units sold by a Big Box store. This Kohler model has an L after it - and that means that it is a slimmed down verson built just for the Big Box store. It has a manual governor for the RPM (which you don't want) and no digital frequency control (which you want). This keeps the price down - but it is not a good unit if you have computers and modern electornics - all of which need very tight frequency control on the power.

I don't know if the Generac models sold by the other Big Box brand is a slimmed down version too - but my guess would be yes to keep the prices down.

The Onan generators mentioned about are very good - but Costco stopped selling the RS12000 (the 12 kW) version which is all I need. Otherwise - I would have already purchased that unit from Costco.

Make sure you look at the spec sheets of the gen sets to understand the true amperage ratings of the units, and also make sure that you size the generator properly so that it can handle the peak load when the AC kicks in.

Also - familiarize yourself with the different types of automatic transfer switches. I wired up my house so that all circuits I need backed up are in a seperate 100 Amp sub-panel. This configuration allows me to use a Service Disconnect ATS - which is simpler to install than the other type of ATS which has individual breakers in it.

I received a price quote for a Kohler 12 kw system, delivered, completely installed, and tested with all inspections for $8500. The same unit on norwall.com is about $4000 delivered. I decided that I could install the unit myself - even subbing out some of the work - and get it done for about $5500. So I put my plan on hold until this summer and will order then and manage the install myself.

Let us know what you wind up buying and where you purchase it from.

Well...tomorrow I am going to give Generac my business. I am going with the 18kw unit and run 2 1.5AC units, a ref., a few lights, and maybe a few other things such as the sec. system. I am paying right at $5200 for this as compared to almost double for the Onan the same size. I have read and read and can not find anything of size from keeping me from buying the Generac. If anybody has anything to add, please feel free to comment. I have 15 hours and counting to make a decision that will affect myself and my family.
Thanks for all of the comments and i will continue to update through the process.
MS

Hi Mr. Mattasimms,

I think the cost difference you are seeing is what you get in the box so to speak. A more expensive generator set is likely to be lower stressed and will last longer. However for the average homeowner looking for an emergency system this is usually not that big of an issue.

The main reason for the difference in price are:

1) The Generac is an Air cooled unit. Lighter and based on lawn mower engines. Typically these run faster at 3,600 rpm.

2) The Onan is a car / truck engine based generator system. It runs at 1,800 rpm. Note that Generac also have a 18kw generator but car engine based. This is it's QT Quiet line.

3) A slower spin speed means less wear and tear. Also the generator rating is different in that you have peak vs sustained power ratings. Peak ratings may be only recomended to be sustained for like an hour say. Again for the average homeowner this is not that much of an issue in that your geneset is only going to be used occasionally.

4) A slower spin speed means the Onan will have 4 windings on the generator head, vs. 2 windings on the Generac to give you your 60 hz. Hence the slower spining generators usually have more copper in them.

5) A slower spin speed means less noise. I think noise is the most immediate noticable difference you will notice. To get a gauge of the amount of noise expected compare a car at 1,800 rpm with your petrol lawn mower. Note however since this is only for emergencys, this is not such a big deal.

6) Weight. The car engine based generator sets weight about twice as much as the air cooled ones. So by weight, i.e. the amount of copper in the genset you sort of get your money's worth. Note that because of the weight, the car based genset can be considerably more expensive to install. You need a back hoe or small crane for the car engine based generator sets.

8) More copper in the generator head usually means the generator can supply a greater starting surge load. Important if you have motor loads. E.g. Air conditioning compressors.

Note you may also need to have permits. I.E. where are you going to put your generator, and your local building inspector may need to come out for electrical, site and plumbing inspections. (Plumbing is for the gas hookup).

Good luck with your installation.

Warmest regards, Mike.

The onan is a lot more - but have to agree with stinkytiger above. The kohler's are more than the generac's but less than the onan - maybe a good balance of performance and cost.

I hope you are not purchasing the generac from the big box store. If you are - swing around to the back of the store and see what brand of generator they use for their backup power (it's a kohler at all 3 of the local big box stores I visited).

You also need to be careful about parts and repair. Everyone I have talked to about the Generac has told me - yes it is cheaper initially - but over time you will loose these savings with repairs.

Good luck.

I am still on the hunt. I had a lot going on at work and could not find time to order last week. I did finally get in touch with the Kohler sales person and I am now going with the Kohler. I just did not feel right about buying the Generac and did not want to spend the $$$ for the Onan. I initially heard not so good things about the Kohler...but it seems that they have gotten better in the last few years. I am looking at the 17kw model and will be calling them in the morning to make the deal. All together it is going to be $7k installed.

matta

7K installed sounds really good. The Kohler's are very good units - I think that is a good choice. Just don't buy the 17kW Kohler that has an L on the end of the model number. The L model does not have the digital frequency control and it also has a manual speed control - two features you do not want.

Keep us posted on how the install goes - I am going to purchase a Kohler myself later this year - probably the 12kW model.

I am the proud new owner of a Kohler transfer switch. I got the one that the fire department can access and shut off from the outside. It was a few pennies more, but salesperson was good! They let me do it in 2 shifts. First get the transfer panel installed and then get the generator when we are ready for it (2 months)...

I am truly glad that I waited and got what i wanted. Now, I have to make a list of who can come over when the gride fails for months on end. Anybody know how to store a years worth of food?
MS

Here's a link to a manual on preparedness. Very good information after the motivational part.

If your scenario is a week without power in one city, that's perhaps reasonable. When you talk about a month, I'm not sure. The problem is that a few prepared individuals may not be able to deal with the rest of the former society. If the national grid went down for a month, it would be like Hurricane Katrina in every city in the country.

Here is a link that might be useful: Preparedness

what type fuel you going to use? the county has a couple 30kw propane kohlers and they are work horses. the only problems they have had were related to ice, freezing up the regulator(takes 2 one at the tank and 1 at the genny) and a couple times before they put a shed over them freezing the stack shut. when you put it in make sure the exhaust and the regulator are protected from blowing rain, as in cold weather this will lead to ice and a failure to crank.

and it ain't no fun standing outside in 30degree blowing rain trying to unstick a regulator!

I am going to be running LP. My new place is about 10 miles from Nashville, so they do not run NG that far out. My Kohler is going to be situated by the AC units that is hidden in a corner of the house. Being in TN, i really do not think that i have to worry tooo much about ice, but you never know. I also think that my gen. does not have a stack...but everything hidden inside the outer shell.

thanks for all of the help! I will post an update when i get everything up and running. I am picking up my Transfer Switch tomorrow and cant wait!
MS

i hope everything is okay for you, your area got torn up pretty good yesterday.

most of the residential units don't have a stack, but i have seen a couple with it.

as far as worrying about ice, we are 6 hours SOUTH of you and get it a couple times each winter, though usually just a light coating. but it does not take much to freeze the regulator and if the unit does have a stack, the flapper on top must be kept clear of all obstruction. you can actually hold your hand on one and try to crank it and it won't fire up, too much back pressure keeps the motor from firing.

Just when i thought that i had everything ordered and under control...i was wrong! After talking with the electrician he really needs a lot bigger generator to work correctly in my house. I am still sticking with Kohler but a lot more Kohler than i ever imagined buying...or needing. I now am looking at the 35Kw beast. It is about twice my budget, but it is really what i need to run a 4 ton HVAC and everything imaginable! This one will have to be delivered by CRANE!

Will update soon!

Hi,

35Kw is quite large. You must really have a large house or / and need to have your A/C connected and running. Usually the compressor units are the things which require the max power, especially when starting. Note that now you are in this sort of power bracket, going even larger usually only costs only a few percentage points more. The big cost, of instalation, back-hoe, crane etc. is already in the budget.

For my installation I only have part of my house powered up and not the whole house. Non essential circuits are left off. The way the installation is done is to have two, 200 amp breaker panels. One panel's circuits are generator backed up, the other is not.

As for installation you need to try and schedule things carefully to save some cash. You will need a back hoe to dig trenches for your Propane gas lines. Usually the same back hoe can be used to lift and install the generator.
Also if you have a back-hoe on site anyway, consider burrying the propane tank too.

Propane tank size wise, I have a 400 gallon for a 20 kw generator. I think you need something like a 1,000 gallon tank. Check the fuel consumption for a 35Kw it could be like about 2-3 gallons an hour. A 1,000 gallon LP tank actually only holds 800 gallons of propane, you need a 20% gas-buffer zone in the tank.

Some people avoid needing such a large generator by forgoing the A/C requirment, or simply buying a smaller window A/C for the days that the power is out. They simply run the window A/C in one room, and that is like the refuge room. This of course does not help if you are trying to protect antiques or art that you may have in your house.

I think as you are finding out, 35kw is like a much larger project. I was sort of surprised at the scope of things too.

All the best, Mike.

If the 35kw model is anything like the 30kw units I have worked on, you will be one of the propane vendor's favorite customers. A 35 kw set seems like excess capacity for "one AC unit, a few plugs, and a string of lights", even if it is a 4 ton AC.

1 4ton AC unit does NOT need a 35KW gen set.

I have a 15KW generac (not known to be particularly good at starting large loads) and it has NO trouble starting BOTH of our central AC units in the dead of Houston summer. One is 4 ton and the other is 3. Granted they are both very high efficiency units and both have hard start kits installed to help with low gen set voltage but it works just fine. The inrush load is slightly above the gensets rated capacity but its fine. Running amps are well within its continuous duty range.

What else are you trying to keep connected? Electric heat? Electric water heater? You must have some other very large loads.

Sounds like he's trying to power half the neighborhood.
Spec's for a 35KW Guardian.

Model Number 5420
Rated Power (LP / NG) 35/35
Rated Amps @ 60 Hz
240 V, 1(LP / NG) 145.8/145.8
3 Phase Models 0174590SBY
Surge Watts - 240V, 1 Ã 54,000
Surge Amps 225
Engine (Generac OHVI) 4.2L/V-6
Alternator RPM 1800
Enclosure Aluminum
Whisper Test Yes
Sound Level (dBA @ exercise) 60
(dBA @ normal operation) 65
Dimensions (L" x W" x H") 77x34x45
Automatic Transfer Switch (not included) RTS
Weight 1683
Typical Retail Price $11,300

Unless this guy is living in a 20,000 sq ft mansion does he need a generator that big.

Hi,

I think that 35kw is quite large, but I also sort of respect what Mr. Mattasimms electrician said. My electrician also suggested that I avoid putting on the larger of my two A/C compressors, I have a 20 KW Onan.

What the electricians are most worried about is system failure, and in general do tend to over specify a system. A system like this is in the $US 23k range when all is said and done. So any sort of failure is not going to be tolerated. However most engineering projects are done the same way, with a X% safety / over specification margin.

I think a smaller generator will power up A/C units O.K., however there may be other high surge requirments at Mr. Mattasimms site.

Consider the following scenario. Power does off. Twenty seconds later the generator powers up. 30 seconds after that the generator trys to put the house on line. At that point in time you may well have all the A/C units, well, fridge, air handlers, freezers all trying to start up at the same time. This inital surge can be handled by starting one thing up at a time, however what happens when the homeowner is out. That inital surge has to be handled automatically. Unfortunately the transfer swtich does not layer in power draws one section at a time, but rather just like Frankenstein, it is all in one big klunk.

Too low a voltage in motors cause the motors to start up more slowly, and hence due to the lack of a "Back-EMF" from a spining rotor, will draw more current. More current means more heat, and in the worst scenario, destructive over heating. Usually a generator will sense over current, under voltage and take itself off line again to fail safely.

Without more knowledge as to what is exactly on site, it is sort of difficult to judge if 35 Kw is really too big. A second opinion from a few electricians with generator experience will be useful though. Unfortunately electricians with larger generator experience are not that common due to the large cost / scale of such a project; these projects are rare.

In the absense of further information, I would therefore recommend going with the 35KW recomendation.

Warmest regards, Mike.

P.S. the specification given by Mr. rjoh878646 I think is not quite right in that most Residential Backup generators are not 3-phase, but Single-phase. The other information looks about right though.

I beg your pardon, If you look at the specs the amperage ratings are stated for single phase.

I = W/E 35,000/120v = 291.6 A 35,000/240 = 145.8 A

Big Generator Protection Half the Price.
More power, more features and an exceptional price make the GUARDIAN QuietSource 16 kW the best value in automatic standby generators. With GUARDIANs new breakthrough technology, the 16 kW provides the circuit protection of a much larger generator at a truly remarkable price. If you need to run more than one air conditioner, the GUARDIAN QuietSource 16 kW is the affordable solution. With 33% more circuit coverage than our 13 kW, this powerhouse can start a 5-ton AND a 3-ton, or two 4-ton air conditioners with plenty of power to spare.

Sounds like he needs something smaller than a 35KW generator unless he plans on supplying half the neighborhood. If a 16KW Generac will start 2 4 ton air conditioner units and run both with power to spare a 35KW unit is overkill.

Found specs for a 4 ton air conditioning unit With a SEER of 13 and the current rating is 40A @ 240v

Sounds like this guy needs to sit down with a calculator and figure his loads out and size the generator properly. You do not need to run the whole house on the generator. just the essentials and some lights. Frig,freezer,air,lights,TV. CFL's will draw less current.

"You do not need to run the whole house on the generator. just the essentials and some lights..."

It isn't always about the need. If I am ever able to buy a "new" standby set, you can safely bet that it will be able to run everything in my house including the Christmas lights and so on. I still think 35kw is a bit large, but given the choice between too large and too small, fuel is cheap when compared to a cold, upset wife.

matt

I think you should get a second opionion on the gen set size. 35kW is too big for what you are trying to do.

I have a 6 ton Geothermal unit and the mAX amps required for that are less than 50 amps. You need a beefy genset - but not 35 kW worth. I would need 50 *240 or 12000 watts to run my 6 ton unit. Something does not sound right.

If you have a 4 ton unit and the traditional other backup things - the most I could see would be a 20 kW, but i think the 17 kW Kohler you were going to buy would be fine too.

Before you make the purchase I strongly suggest getting another input.

matt

I hit the send button too soon. At 35kW and 240 volts, that equates to 145 amps. Check the size breaker that is feeding your 4 ton AC unit - no way it is a 145 amp breaker.

I bet that you have a 40 or 50 amp double pole breaker feeing that 4 ton unit. if that is the case - and that breaker is not tripping when the unit starts now - why would you need 145 amps to start your unit?

Something does not compute. I am not an electrician nor a genny expert - hopefully some expert can chime in here. I am very curious on this sizing question.

matt

here is some info that might help. I just checked the Costco web site for the 12kW Onan which is the genset I want - but Costco stopped selling it for awhile. I know why now - Onan has a new product.

If the 12 kW Onan can hanlde a 4 ton unit (see below), I believe you would be safe with the 17kW Kohler

I hope this helps

RS12000 with 100Amp ATS, $5700

Extreme weather, construction activities, and countless other unforeseen power complications can suddenly interrupt the electrical service you and your family depend on to continue your daily activities and routines. The RS12 is connected to Natural Gas or Propane. This new unit is aesthetically designed with an all climate enclosure. The system can power a 4-ton air conditioner yet very quiet at 64dB(A) (7m @ full load). Not only will it provide you with power but it won't disturb your neighbors.

Rated power: Natural Gas; 10.5 kW LP Vapor 12 kW LP
Rated amps: 87.5/43.75 Natural Gas; 100/50 LP Vapor
Engine: Subaru EH 72, 4-cycle air-cooled, 2 cylinders OHV
Fuel consumption: 191 ft3/hr at full load NG, 88 ft/hr at full load LP
Circuit breaker: 50 amp, 2 pole
Voltage: 120/240 VAC, single phase, 1.0 pf.

When sizing a generator for An A/C unit you need to take in consideration the Lock Rotor amps which on a 4 ton a/c unit can be near double the max current rating is for a few seconds. A 4 ton A/C current rating at 40 amps at start up LRA can be double that for a few seconds.....Once it gets started it will drop well below that 40 amp rating normally (RLA). 40A is just the max for current protection when sizing wire and breakers.

35kw is big enough to run anything you want. one thing to keep in mind is that you have to balance teh size with the load and desired fuel consumption. going bigger means the motor has less load on it to provide what you need and therefore up to a point uses less fuel. but if you go way oversized then even running under a light load will use more fuel than a smaller unit running at 50% capacity or even full load capacity.

the county here uses 30kw genset to run their tower sites. with everything up and pulling max power(not uncommon at all) they pull well over 20kw continuous. a 500 gallon tank lasts them a few days under this condition. when they sized it they wanted to go with a 50kw, but found out the fuel usuage would mean filling the tank every other day versus the current 4-5 days per tank.

BTW, when i get the money to put in a larger genset i will be going with either a 20 or 30kw. probably 30, since my house has 2 HVAC systems and in heating mode when running on the strips they will pull close to 30kw JUST for the strips. my front unit is a HP, so it only runs on the 19.2 kw strips in emergency mode, so i can force it to not use them if i had to for power saving. the rear unit is strip heat only, so it will always draw about 15kw for them.

i am right there with you guys..i think that it is overkill, but i have a few rebuttals....

1. 30Kw is air cooled and 3600rpm
35Kw is water cooled and runs at 1800rpm which is half the stress on the genset

2. my heatstrips on my electric HVAC require a lot of power. these need to be able to heat my house on the emergency heat setting....generator only runs during emergency times and i would kick myself WHEN something does happen and i am ALMOST prepared...

I am about to throw in the towel on this generator thing...it has caused all kinds of hell on the construction site and i am not sure if $15k is best spent on this. i may get everything ready for a generator install in a year or so. with the money consumption of building a house...there is always something else to spend $15k on....

on the other hand....i am going to do it!!! better safe than sorry!

Hi,

One thing to note is that if you install the generator when the house is under construction, you have heavy lift on site. Installation cost will therefore be less. Note trenching for the LP Propane gas lines needs a back-hoe.

However you can delay to add a genset later, I did. Right after we were blacked out for 5 days. It was not pretty. What I missed most was no water. Toilets sort of get stinky!

If you are rewiring, then ask the electirican to split your power wiring into two broad catagories, generator backed up and not backed up. Then have a sub panel for each and wire in the circuits with this i mind. My electrician had to move circuits and rewire my panels a bit when I installed my genset. Also make sure you have enough room on the wall next to the panels to put in a transfer switch. For a 200 AMP transfer switch you need quite a bit of room.

Also have installed while the wall are open some wire ducting / pipe that will bring the wire from the generator into the mains panels. This pipe should be a pair. One larger one of the power lines + battery feed, also a smaller pipe for control lines.

My genertor has:

1) Power lines for generated power
2) Low voltage battery tender charge lines
3) 120v circuit for the pre-heater on the cooling system. The cooling system is maintained at a warm temperature, so that the genset can go online fast.
4) In a seperate conduit, control wires between the transfer switch and the genset.

If possible at least decide where you will put the genset. One guy in our neighbourhood placed his Genset away from his house by about 20 meters. So when it runs it is quiet. He brings in the lines underground. Much quieter and lower risk of CO poisioning. This works if you have the room and not too near a neighbour.

For a 20kw and over, genset you need a concrete pad. You can pour this and get it ready. The key gotcha is you need detailed plans of the genset. The pad typically needs bolt down fasteners positioned to bolt into the underside of the genset, and also have your wiring condits bought in from underneath the concrete pad at the correct position. Gensets change specifications all the time, so if you do do this in advance (cheaper because you have equipment on site anyway) do not delay too long in case the genset you planned for has a specification change.

Good luck. I can certian appreciate the decision over load. When you are building your GC is lways wanting you to decide in tile, paint, wood finish, wiring. A gen set is just one more decision, and is quite a complex install. You are often stuck in trying to make a good decision on the one hand, but time preasure is always against you.

Warmest reards, Mike.

matt

backing up the heat paks seems like another overkill to me but if you want that then i could see needing the 35kw. my 3 ton units need 30 amps for heat pump mode but another 40 amps for the heat paks.

the LRA on my 3 ton heat pump is 17 amps the total is 22 amps. the max load is 30 amps - so they use 10/2 wire and a 30 amp breaker. your 4 ton should be a little higher then that - probably a 40 amp circuit. the heat pak might be another 40 amp or 50 amp circuit.

it's a question of how much backup protection you need and what your nightmare scenario is. if it is a summer outage - then you need AC, water, friges, etc. If it is a winter ice storm (that is the scenario i designed for) then you need heat, water, etc. if it is both - then you have to size the genset for the worst case.

What I did was install some really nice fireplaces that operate as heaters and will use the backup gennny to power the fans and controls for them. this way - i get to enjoy the fireplaces year round and the genny is smaller. i can get the genny for 5 grand and i spent another 8 grand in fireplace upgrades. if we have a summer outage - our plan is to hang out in the basement where it is cooler. we can take a lot of heat as long as we have water and the refrig's backed up. but freezing to death is not an option. had i designed to have all my heat pumps running with aux power too, i would have become a small power company and would have needed a gigantic propane tank.

you can put all your money into the genset - but think about how often you will really use it. if you are worried about backing up power for all situations - then go with the 35kw. it just seems like a lot of cash sitting there not being used most of the time.

UPDATE UPDATE UPDATE

I am going to get the original 17kw Kohler. I gave it lots of thought and what started as me wanting a portable Honda generator had me getting $15k in generator....

I am back to a smaller more affordable (7k)set that will be running the 4 ton unit, minus the emergency heat. i am not sure how this is done, but it is being done.... i have 2 gas fireplaces that will help keep the heat tolerable when we have the next ice storm, and you know that will never happen again in TN. it all comes back to that one time we were out of power back in ...i think 92ish??? but being prepared was what i was taught as a boy scout...so i guess it could be some kind of weird marketing ploy by the generator manufacturers around the world...:)

i think that i will be happy with my decision. i know that in an emergency situation, we always could have used more of anything...being this close to nashville...i bet i can manage a few uncomfortable days reading a book, instead of typing on a computer.
MS

If considering a generator and you have lots of electronics such as home automation the smaller Generac Guardian is causing problems which Generac says it not a warrantable issue. The low mass, quick governor response design is responsible. For Zwave devices it can stop all communication but the dimmers and switches do still operate the old fashioned way. For lighting systems that attempt to stabilize voltage it can cause flickering lights while the generator revs up and down. For those with the budget for the toys don't try to save money on the generator. It is best to go with a higher mass generator with more stable voltage and frequency even if you don't require the load capability. The 4.2 liter V6 powered Generac has been suggested as the minimum for homes that contain a lot of expensive home automation electronics if you want them to actually work during a power outage.

dim

Have you heard anything bad about the Kohler gensets (not the one they offer though Lowe's) wotking with computers or dimmers? I talked to a company and asked them about the Generac's and they mentioned that the frequency control was not good enough for high end electronics - and that is why they recommended the Kohler.

I also had been looking at the Onan 12kW sold through Costco - and that is supposedly a very good unit. I was trying to figure out why the Kohler 12 kW runs about $4200 with 100 amp ATS while the Onan 12kW unit is about $5700 (on sale, reg $5900) with 100 amp ATS. Is the Onan worth the extra 1500 to 1700 dollars? What exactly does the Onan have that the Kohler doesn't - or is it just the cost due to brand name?

Costco stopped offering the 12kw unit for a while but have now started carrying it again - so I am now considering the Onan once again. The reason I ask is that as you know from my previous posts - my house is loaded with Insteon dimmers and controllers. I want to make sure that the genset does not damage any of that stuff (which works beautifully by the way - DW loves it!)

The last thing iwant to do is fry all of my electronics - which are also imbedded in just about every appliance we have.

Thanks

Hi,

Voltage regulation is something that some people on the net have mentioned. The Cummmins / Onan engineer who came to turn my genset hooked up to it via a interface and linked it up to his PC. From there he could monitor Volts, Current, Frequency along with about 148 other parameters, oil pressure, temp of engine etc. And also control various parameters for stability control. For the Onan's there is an interface acessory that allows remote monitoring via the internet, this I think is sort of more designed for remote un-maned relay transmitter applications.

He mentioned that one client had an elevator in his house, and when that started it was giving the generator a hard time. Fortunately he said he could tweek the Onan generator control parameters to take this surge into account. The most usual symptom of bad regulation is when a large demand kicks in, your lights sort of wobble a bit. If this persists you may have a control issue.

Electronics are sensitve to surges. However most modern TV's etc. power supplies have some protection built in, you can also buy surge supressors cheaply at home depot. I go for the $US 14-ish ones. I also had an electician installed whole house surge suppressor at the main panel as well. Some people say you need XXX type surge supressors, others say the cheapies are O.K. I sort of am not sure, so sort of go for a medium-ish sort of price product and only put them on the more expensive electronic items.

I think there is a price trade off on this stuff. You can have a super dooper protected system, but if you are in a somewhat low risk area, it may not be worth it. So I guess each person has his / her sort of level of backup requirment.

Incidently if yo are looking for a cheap gasoline powered generator for electronics, many people on the net recommend the Honda inverter generators. The largest is the Honda IS7000 AB. This guy actually spins at various speeds and generates a DC voltage / current. It then has built in power electronics which converts this to 60Hz AC, and produces very clean and stable power. Note cheap in this case still means about $US 3400.

All the best, Mike.

sniff

I've not heard comparisons between Kohler and Onan or anything bad about Kohler.

I misspoke about Zwave. It is Insteon and UPB devices that don't like the little Generac Guardian because of the way they communicate over power lines.

dim - thanks - that is very useful info. I have way too much time and money into my insteon setup to mess with that. the kohlers are not that much more than the generac's - so i will at least purchase the kohler but am still considering the onan.

mike - thanks too. can you tell me where you purchased your onan? was it from costco or a local shop? I would like to get the onan - but the closest service center is quite a diatance away (150 miles) and that concerns me. there are local kohler services in my area - within 30 minutes.

also - I am planning to install whole house surge supressors. I have the 100 amp sub-panel with my backup circuits tapped off one of 3 main panels (200 Amps each). SHould I put in 4 surge supressors - one for the sub-panel and one for each of the 200Amp mains?

thanks

My whole house Insteon installation works fine while running on the 15kw Generac. Never noticed any more instablity than it normally has.

Other than the kitchen oven, garage air compressor and welder, our entire house operates as normal on the generator. Been very pleased for its $3000 cost vs nearly double for its competition. It is now nearly 3 years old and works just fine still. Will likely need some touch up on the steel enclosure this summer. So far so good.

I was out picking up my transfer switch at Kohler and took a look at the 30kw that i was thinking of purchasing...I drive a toyota tundra double cab and that generator was almost the same size. I do not know what i was thinking, but i am so very happy that i stayed with the 17kw...it really will do what i need it to, and not cost me 15k$$...more to come as i get this thing installed..

Hi Sniffdog,

I purchased my Onan from Costco (See post earlier in the thread for experience of the process). The service I received was from Cummins Metropower. They are not really a dealer per say, but a distributor, i.e. one up the chain of command so the speak. These guys are quite expensive, but I would rate their service as really first class. Note they also came out three seperate times free of charge to fix installation and defect issues. They also did not drag their feet. They said they will come out, and they did right away. They are I think about 25 miles from where I live (Westchster County, New York). They are based in the Bronx, New York.

best, Mike.

Here is a link that might be useful: Cummins Metro Power

mike - thanks.

I have to give them a call.

Locked Rotor Amps on a motor is usually 4 to 5x the normal operating voltage of the unit. That is the guideline. Now, granted that that isn't always the draw and it's usually momentary (not even a few seconds), but nonetheless for LRA - they usually recommend 4 to 5x the operating voltage. To safely operate a hvac unit, most people say you need/want a generator in the 17.5kw range for a moderate sized hvac unit. That size will generally handle the starting loads of many hvac units.

For sensitive electronics, you want true sine wave output, electronic governors and generally +-1%. It generally isn't achievable on 3600rpm or cheaper units but the better made units can and will easily handle this.

35kw equates to about 140amps at 240 or 280amps at 120. It's a decent sized generator to use for a moderate sized house (full load) or large sized house (selected loads). Keep in mind, that the NEC 2008 (which isn't universally adopted yet) code requires generators used for whole house lodas (not selected loads) to be sized to handle the entire load. So, if your house was sized for 600amps, you need to handle that load if you wire for whole-house. In the past - you didn't have to do that - you could just protect your generator with the sized breaker for the generator and if you ran out of juice, you ran out of juice. Apparently the NEC put this in because of 'critical' people in Florida who had entire house loads put on generators that couldn't handle the entire house. So, since they didn't understand that they had to shed load to allow the generator to work, the generator failed. So the new NEC code put in language that that wasn't allowed anymore (which I personally think is stupid, but thats neither here nor there).