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pandora
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Decent 20-30 KW standby generator

I've been considering a Generac air cooled 20 KW generator, but there seem to be an unusually large number of horror stories. I've also read that 1800 RPM liquid cooled run longer / better.

The Generac 20 KW generator needs maintenance every 200 hours of operation, my worst case assumption is 2 weeks of no power.

That's a bit over 200 hours. Does anyone make a standby generator in the 20-30 KW range that has a 400 or longer interval between required maintenance?

I already have 2 200 amp Generac automatic transfer switches, and have a 1,000 gallon propane tank on order. If I have to, I'll go with the 20 KW air cooled Generac, but I'd like to be able to run longer than 200 hours at a time without having to stop and run maintenance.

Thanks for any suggestions.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1

You may want to look at Diesel units since you are looking at a 20 KW. I googled it and there are some that run at 1200 rpm.

Here's what I googled "20 KW Diesel emergency generator"



Coma
Thanks Steve
Premium
join:2001-12-30
NirvanaLand
reply to pandora

Last year I was looking at a Kohler 20REOZJC to locate next to my fuel oil tank but never acted on it.

--
November is National Epilepsy Month



Jack_in_VA
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said by Coma:


Last year I was looking at a Kohler 20REOZJC to locate next to my fuel oil tank but never acted on it.

Looks like $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

It appears to be a nice unit. Did you get a price?


dennismurphy
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join:2002-11-19
Parsippany, NJ
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reply to pandora

I'm doing research myself... I haven't been impressed with what I've read about Generac, but the Kohler models seem to be the way to go. The 5-year warranty alone helps seal the deal for me.



PSWired

join:2006-03-26
Annapolis, MD

I'd go for Generac's crappiest air cooled model over any of the chinese diesel generators available. Who cares about the maintenance interval if the whole thing fails in the first 100 hours.

Generac, Kohler, Katolight, Onan are brands you should be looking at. 1800 RPM and liquid cooled will be a good combination to maximize maintenance intervals.



ITICharlie1
Premium
join:2003-01-22
Saint Louis, MO
reply to pandora

I just have to ask, why do you need one so large? Is it for a business? I can run everything except the central AC on my 7000 watts gas genny.
--
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fifty nine

join:2002-09-25
Sussex, NJ
kudos:2
reply to pandora

If I had to buy one I would buy a Cummins-Onan. Costco and our local co-op sells them.

I don't like generac one bit.



fifty nine

join:2002-09-25
Sussex, NJ
kudos:2
reply to ITICharlie1

said by ITICharlie1:

I just have to ask, why do you need one so large? Is it for a business? I can run everything except the central AC on my 7000 watts gas genny.

Maybe he wants to run his AC.


nunya
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1 recommendation

reply to pandora

Wasn't there just another thread about this same thing? You already have the Generac ATS, so you need to look at Guardian, Generac, Siemens, or Centurion.
--
If someone refers to herself / himself as a "guru", they probably aren't.


Bob4
Account deleted

join:2012-07-22
New Jersey
reply to pandora

Some folks here have generators with inverter outputs. They say they're much quieter, are more efficient, and produce cleaner power.


pandora
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reply to Jack_in_VA

said by Jack_in_VA:

You may want to look at Diesel units since you are looking at a 20 KW. I googled it and there are some that run at 1200 rpm.

Here's what I googled "20 KW Diesel emergency generator"

It's gotta be propane, sorry.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"


fifty nine

join:2002-09-25
Sussex, NJ
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reply to Jack_in_VA

said by Jack_in_VA:

You may want to look at Diesel units since you are looking at a 20 KW. I googled it and there are some that run at 1200 rpm.

Here's what I googled "20 KW Diesel emergency generator"

I think those are pulls from refrigerated rail cars if they are the same ones that you are seeing. They are 3 phase though.

pandora
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reply to ITICharlie1

said by ITICharlie1:

I just have to ask, why do you need one so large? Is it for a business? I can run everything except the central AC on my 7000 watts gas genny.

Two 4 ton heat pumps are my ONLY heat source. Both must be able to operate. Two electric heaters can use up to 4.3 KW a piece. 20KW is the floor for my home to remain comfortable. 20 KW is the highest wattage an air cooled generac will provide, after that it's liquid cooled.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

Mr Matt

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reply to pandora

You might want to verify that the transfer switches you purchased are compatible with the generator you purchase and if two transfer switches can be used with the generator that you purchase. Generac offers transfer switches for their air cooled generators and different transfer switches for their water cooled generators. Some older model transfer switches are not compatible with newer model generators.

Kohler just introduced new water cooled propane powered generators. The new models are 38 KW and 48 KW, around $14,000.00 and $16,000.00 MSRP. The difference in price between a 38 KW and 48 KW generator is about $2,000.00. Here is a list of generators including 38 and 48 KW generators. You will find that a water cooled generator from 38 to 48 KW cost about $10,000.00 over the cost of a 20 KW air cooled generator. It is important that you select a qualified installer because even the most reliable generators will not be satisfactory if not installed properly. Here is a price list for Kohler water cooled generators:

»kohlerpower.com/onlinecatalog/pd···mall.pdf

General Electric/Briggs and Stratton have just introduced new model generators, you might want to check them out as well. Home depot lists Kohler, Generac and General Electric water cooled and air cooled generators. I strongly recommend downloading and reading the owner manual for each generator that you are considering, to learn the maintenance intervals advantages and limitations of each generator.



Coma
Thanks Steve
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join:2001-12-30
NirvanaLand
reply to Jack_in_VA

said by Jack_in_VA:

Looks like $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

It appears to be a nice unit. Did you get a price?


I can't remember specifically but I think it was in the 8-12K range.

--
November is National Epilepsy Month


leibold
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Sunnyvale, CA
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reply to pandora

I don't know whether noise is important to you (it may be if you want to keep the generator running at night) in which case the Generac QuietSource 22kW (liquid cooled) might be a good choice.
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TheMG
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Canada
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reply to Bob4

said by Bob4:

Some folks here have generators with inverter outputs. They say they're much quieter, are more efficient, and produce cleaner power.

The problem with inverter generators... when the inverter fails, the generator is completely useless and the repair is usually very costly (usually the entire inverter module needs replaced). Not as much of a problem with good quality units that have a good warranty, but it's something to beware of with the cheaper inverter units.

Also, "cleaner power" is highly debatable. A good quality non-inverter generator can have a very clean output waveform and tight voltage and frequency regulation. Maybe if you're comparing a decent inverter unit with a cheap-ass non-inverter, then yes the inverter will probably have better quality power, and that's assuming the inverter isn't one of those "modified sine wave" units.

The main advantage of an inverter setup is that it is the inverter that produces the output AC waveform and thus the inverter sets the frequency, this means the output frequency is independent of engine speed. Therefore, the engine speed can be adjusted depending on the load in order to improve efficiency and reduce noise during low or medium loading conditions. In contrast, since a non-inverter generator's output frequency is dependent on engine speed, the engine must run at a constant speed all the time.


cowboyro
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Shelton, CT
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reply to pandora

Re-think the heating solution (if you have propane then use it for auxiliary heat).
I've been without power for over 6 days after Sandy, my 7200W generator was able to power the entire house without any issue.
Honestly it makes absolutely no sense whatsoever to use electric aux when you have propane, the break-even price is around $4/gal for $0.16/kWh, you can get a propane generator to handle the entire house for under $1000 while a big-ass 20kW propane generator is in the $5000 range.
Not to mention you'd be using some 2.5gal/h at 50% load, one week without power will run you in the $1000 range for fuel.
And one more thing: the delivery capacity of the tank. Depending on temperature and humidity even a 1000gal tank may be unable to supply enough fuel without frosting.


TheMG
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I agree with Cowboyro.

You'd be much better off using the propane to heat the house directly. The money you save by getting a smaller generator could easily cover the cost to install a gas furnace as an emergency heat source.

You'll also save a lot on the cost of running the generator. Conversion of propane to electricity is very inefficient, so even with high efficiency heatpumps, when you consider the big picture, you'd be burning much more propane heating the house with the heat pumps than with a gas furnace.


pandora
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reply to nunya

said by nunya:

Wasn't there just another thread about this same thing? You already have the Generac ATS, so you need to look at Guardian, Generac, Siemens, or Centurion.

Yes I have 2 Generac 200 amp ATS switches on a soon to be installed 400 amp service.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

Mr Matt

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reply to pandora

I would expect that the power required by both of your heat pumps running in the defrost mode simultaneously would be 24 KW or approximately 100 Amps or 50 Amps each. The maximum continuous power from a 20 KW generator is 83 Amps. If you want to be able to use most of your appliances at the same time, you should consider at least a 36 KW Generator, which will provide 150 Amps @ 240 Volts. Since you are having a 400 Amp service installed, for the difference in price I would consider a 48 KW generator.


pandora
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reply to TheMG

said by TheMG:

I agree with Cowboyro.

You'd be much better off using the propane to heat the house directly.

No chimney, no flue, no way to vent propane at this time from inside the house (other than cooktops).
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

pandora
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reply to Mr Matt

said by Mr Matt:

I would expect that the power required by both of your heat pumps running in the defrost mode simultaneously would be 24 KW or approximately 100 Amps or 50 Amps each. The maximum continuous power from a 20 KW generator is 83 Amps. If you want to be able to use most of your appliances at the same time, you should consider at least a 36 KW Generator, which will provide 150 Amps @ 240 Volts. Since you are having a 400 Amp service installed, for the difference in price I would consider a 48 KW generator.

I think 30 KW is about it for an above ground 1,000 gallon propane tank in terms of gas flow to drive the generator.

As to defrost, I tend to doubt that much power is required.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

TheMG
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reply to pandora

said by pandora:

No chimney, no flue, no way to vent propane at this time from inside the house (other than cooktops).

Modern high efficiency furnaces don't require a chimney. The flue is essentially just a couple of plastic pipes. Ours just runs straight out the side wall of the house nearest the furnace.

The furnace would install in your existing ductwork, assuming you have ductwork in place already.

averagedude

join:2002-01-30
San Diego, CA
Reviews:
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Click for full size
concentric vent sample
I have to agree with TheMG on this.
Todays furnaces use PVC piping for the combustion air exhaust and intake.
You can run the pipes through the roof or exterior side wall.
Most (if not all) offer a Concentric Vent kit that pipes both combustion air and exhaust in to one pipe so there is only one penetration through the wall or roof.
You can even paint out the pipe to hide it.

Edit
In addition, because the combustion air is piped it, you don't have to worry about combustion air louvers or the furnace using warm room air for combustion air.


nunya
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reply to pandora

We just went through this in another recent thread, and the OP tends to believe that the defrost heaters aren't necessary even though I tried to explain otherwise:

»Anyone have a suggestion for standby whole home generator?
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Mr Matt

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reply to pandora

What is the name plate amps on the condenser and air handler of your heat pumps. Your heat strips already draw about 18 Amps at 240 Volts. Each condenser will probably draw about 25 Amps and each air handler exclusive of your heat strips 5 Amps. When in the defrost mode your current requirement should be around 48 Amps per heat pump. Contact your HVAC contractor and confirm.

The last thing you will want to do is purchase a generator that cannot carry the offered load. I would not recommend guessing because the information is already on the specification plates on your air handler and condenser. My 3.5 ton condenser requires 20 Amps my air handler requires 5 amps and my 4.8 KW heat strip requires 20 Amps for a total of 45 Amps while in the defrost mode. My 2.5 ton condenser requires 40 Amps while in the defrost mode.



cowboyro
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reply to pandora

said by pandora:

As to defrost, I tend to doubt that much power is required.

It's whatever heat pumps+strips+air handler require.
From the specs you gave it will be around 10kW *each*.
You may be able to block the strips if you are willing to cope with ice-cold air being blown at full blast for few minutes (trust me I have tested with aux heat off), but it is very unpleasant. For all practical purposes it's like having the A/C on.

pandora
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reply to nunya

said by nunya:

We just went through this in another recent thread, and the OP tends to believe that the defrost heaters aren't necessary even though I tried to explain otherwise:

»Anyone have a suggestion for standby whole home generator?

When I review the Goodman literature, I see the maximum sustained wattage listed as about 4KW per unit in heat mode. Start up wattage is a bit higher.

I believe defrost is done via reversing the heating units, during that time the air handlers will not blow cool air into the house.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"