need schooling on whole house standby generators

[94yj]

i have 1283 sq ft all electric home with a 4 ton heat pump system and 15kw in heat strips and i just had a person come out for a quote and he said i would have to have at least a 38kw to power the house which does not make sense also it will be running on propane fuel as i do not have gas in the neighborhood and according to multiple sites i have been to say i should be fine with a 20kw system can someone please explain to me why i have to have double + in kw s TIA

 

[Hot Rod Grampa]

Salesmen make commission on total sale $. There are some compromises made when sizing generators, but if you want everything to work at full bore at the same time, maybe his numbers weren’t wrong. Go with someone you trust and will stand behind their product and you will be ok.

 

[jeepxj]

that is the "run the house like nothing is wrong" price.

a 20kw is more than enough for a house of that size with minor inconveniences. no running the laundry, stove and heat strips at the same time.

 

[Tim Kennedy]

94yj:
Go to:
hardydiesel.com

Lots of info & equipment, knowledgeable people.

 

[Randy in Maine]

Do you really need to power up all of that stuff up when the power goes out? Are you on city water or a well? Do you have any sort of back up heating system? I have a gas kitchen stove, my weber, and this little propane woodstove.

 

[manwithtools]

Doesn't your electric bill have your maximum demand listed, something like:
Highest Usage Point (Demand) this month:
8.6kW on Jan 28, 2021 from 6:00am to 7:00am

If you review the last year or so of electric bills, you should see what your house takes to operate. I don't see why a 20kw wouldn't do all you need. With your winter weather, I bet you seldom use the heat strips. Even with them, using another 5 kW would be a lot.

 

[bzinsky]

Cant answer your question

But I will say my next door neighbor just had a natural gas one installed. It starts up and runs on it’s own once a week. If I had to guess it runs for like an hour, not sure.

It’s pretty annoying, and it has to be consuming a good amount of gas. Just want you to factor that in as I’m sure propane isn’t cheap.

 

[ace10]

If you have 15000 watts in resistance heating, that's 75% of full load for a 20kwh gennie.

So you'd basically have a briefcase generator's worth of capacity to run everything else.

You want hot meals? Hot water?

The math don't lie.

We had an all-electric house and I just couldn't swallow the bill for a 40kwh gennie, so we converted heating and hot water over to LP. And we do OK with a 20kwh gennie with a few load shedding switches.


EDIT: Exercising routine is usually 15 minutes. Basically a half gallon of fuel per week to know that all is well.

 

[bzinsky]

i have 1283 sq ft all electric home with a 4 ton heat pump system and 15kw in heat strips and i just had a person come out for a quote and he said i would have to have at least a 38kw to power the house which does not make sense also it will be running on propane fuel as i do not have gas in the neighborhood and according to multiple sites i have been to say i should be fine with a 20kw system can someone please explain to me why i have to have double + in kw s TIA

Upgrade your heat pump to one without strips, then get a much smaller generator = save a lot of money?

Well i guess in texas the heat strips aren’t running much.

 

[reader2580]

I'm sure after the freezing weather a lot of people want a generator that will keep them warm even if it gets cold enough that the heat strips kick in. Are your heat strips set up such that only say half of them can run at a time? Half probably wouldn't keep the house at 72 degrees, but it should keep it warm enough so that pipes are not bursting.

A 38KW generator would use propane like crazy. How much propane are you willing to have on hand in case of an outage? If it is cold again and there is a huge multi day electricity outage at the same time everybody is going to be calling for propane refills. Will the trucks even be able to make deliveries if there is an ice storm?

 

[rlitman]

Doesn't your electric bill have your maximum demand listed...

Around here, commercial bills have demand billing, but I don't think it's tracked on residential bills. It certainly wasn't when I had a mechanical meter. I guess I'll have to take another look at my bill, since we got a smart meter in the past year.

 

[theoldwizard1]

that is the "run the house like nothing is wrong" price.

a 20kw is more than enough for a house of that size with minor inconveniences. no running the laundry, stove and heat strips at the same time.

This ! Probably, less than 10kw if you exclude the water heater. This will require some rewiring of you existing breaker panel.

Long term, you should convert the water heater, dryer and stove to propane. If you live in a warm climate, a window A/C will keep one bedroom cool.

 

[jeepxj]

This ! Probably, less than 10kw if you exclude the water heater. This will require some rewiring of you existing breaker panel.

Long term, you should convert the water heater, dryer and stove to propane. If you live in a warm climate, a window A/C will keep one bedroom cool.

20kw is more than enough to run a 4 ton AC unit and a water heater. just dont be drying clothes and baking cookies with it

 

[jeepxj]

Cant answer your question

But I will say my next door neighbor just had a natural gas one installed. It starts up and runs on it’s own once a week. If I had to guess it runs for like an hour, not sure.

It’s pretty annoying, and it has to be consuming a good amount of gas. Just want you to factor that in as I’m sure propane isn’t cheap.

mine runs for 30 minutes every sunday.

exercise chart says .4 gallon per hour of propane.

full load is 3.6

 

[94yj]

Do you really need to power up all of that stuff up when the power goes out? Are you on city water or a well? Do you have any sort of back up heating system? I have a gas kitchen stove, my weber, and this little propane woodstove.

no mainly the a/c heat system if in the winter and heat strips if below 25 degs and a TV and icebox and on city water and have a fireplace but cannot use it due to past lung issues

 

[bzinsky]

Yeah dude no way I’d install a generator to run a 15kw heat strip. Not only will you need to pay an extra $10k for a generator, the propane, converted to electricity, and then to heat strips, you might as well burn dollar bills for heat.

IMO get a wood stove installed in the basement. Those things can pump out some heat.

I was going to suggest solar panels with a battery backup. But if the power ever goes out at night, you better have a couple tesla sized battery’s to run that heater.

 

[jeepxj]

agreed. i'd pre-buy some cheap 1500w space heaters to have on standby for cold corners of the house. more than enough over head on a 20kw to run them.

 

[rjacobs]

lol, 38kw generator... thats like a 30k+ dollar genset...

Above 22kw Generac goes to liquid cooling and the price go's NUTS...

A 22kw would run my 3700 sq. ft. house just fine. I can only run 1 HVAC system and 1 hot water heater, but beyond that everything else should be usable if I am smart(shut off the HVAC if I want to run the oven). A 22kw Generac, plus install, was 10k when I checked last year(pre covid)... I bet their prices are higher now. Plus since you dont have gas, you gotta get propane(if you dont already have it) so add at least another 2k for a minimum 500g tank.

BUT here is the big thing about a few weeks ago event here in Texas... its SUPER CRAZY RARE. My uncle has lived here his whole life(67 years) and he said he has NEVER seen this happen before and doubts he will ever see it happen again. The power generators and the power deliverers are going to be mandated to fix the glitch and harden their systems for at least down to 0(my understanding is a lot of it is hardened down to 15f already, but to harden to 0 degrees is a crazy price increase). I was without power for 4 solid days... im not running out and buying a generator. We had a small generator I backfed into my panel and it ran a small space heater in our master bedroom. We survived. Might get a cord of wood next October, but beyond that I am not running out too spend 10k+ on a gen set...

 

[Stuart in MN]

A generator needs to be sized to handle startup loads, so you can't necessarily just look at the steady state kW load. I don't know what that would be for your heat pump system but it needs to be taken into consideration. Are there any other motor loads like a well pump?

 

[94yj]

A generator needs to be sized to handle startup loads, so you can't necessarily just look at the steady state kW load. I don't know what that would be for your heat pump system but it needs to be taken into consideration. Are there any other motor loads like a well pump?

nothing other than the a/c heat system and the side by side ref everything else could be cycled through as needed i am not going to have the whole house on at once

 

[Davefr]

i have 1283 sq ft all electric home with a 4 ton heat pump system and 15kw in heat strips and i just had a person come out for a quote and he said i would have to have at least a 38kw to power the house which does not make sense also it will be running on propane fuel as i do not have gas in the neighborhood and according to multiple sites i have been to say i should be fine with a 20kw system can someone please explain to me why i have to have double + in kw s TIA

Set your thermostat to not turn on the heat strips and you can get by with a lot smaller unit. The salesman's calculation probably included 15kw for the strips, a few thousand watts to supply the surge current needed to start the heat pump and air handler, and lots more wattage for the oven, dryer, refrigerator water heaters along with a fudge factor. Decide what you "must have" and the unit can be much smaller.

 

[yeldogt]

A 4T heat pump is 48k BTU's -- that should have no problem heating 1300sf --- my studio is 1700sf and I can heat it with 14k

Also 22k can start a 4T. My cummins says it will start a 5T .... how old is your HP?

The cost to purchase the largest air cooled unit (20/22k) is not much more than the smaller units --- it's best to just get the 20/22K and cut it in between the outside meter and the main panel. My cummins came with the transfer switch -- SE rated for outside 200amp. Makes for an easy install does the whole house and no playing with the existing panel --- when you look at the running costs in propane the larger units running partial loads don't use much more fuel.

Do you ever need the strips with a 4T unit?

 

[94yj]

A 4T heat pump is 48k BTU's -- that should have no problem heating 1300sf --- my studio is 1700sf and I can heat it with 14k

Also 22k can start a 4T. My cummins says it will start a 5T .... how old is your HP?

The cost to purchase the largest air cooled unit (20/22k) is not much more than the smaller units --- it's best to just get the 20/22K and cut it in between the outside meter and the main panel. My cummins came with the transfer switch -- SE rated for outside 200amp. Makes for an easy install does the whole house and no playing with the existing panel --- when you look at the running costs in propane the larger units running partial loads don't use much more fuel.

Do you ever need the strips with a 4T unit?

hp is a new system inside and out and about a year old and the hard sub freeze was the only time i used the heat strips

 

[jade97]

A 38KW generator would use propane like crazy. How much propane are you willing to have on hand in case of an outage? If it is cold again and there is a huge multi day electricity outage at the same time everybody is going to be calling for propane refills. Will the trucks even be able to make deliveries if there is an ice storm?

I am still on my initial 500 gallon propane fill, with the generator exercising 10 minutes per week, multiple outages ranging from minutes to 4 days.Still have 55%. 38kw generator installed March 2018. My house is all electric 3000 sq ft.

 

[manwithtools]

A generator needs to be sized to handle startup loads, so you can't necessarily just look at the steady state kW load. I don't know what that would be for your heat pump system but it needs to be taken into consideration. Are there any other motor loads like a well pump?

15kw of heat strip is much larger than any compressor startup load. Also can add soft starts to the heat pumps and use load shedding modules like the Generac offerings to prevent / offset the bigger loads from starting while on generator.

Edit: just saw the HP is fairly new, soft start technology is probably already included in it.

You need to talk to another generator shop. I suspect anybody in your area in that business is making bank about now, if you don't bite on 38kW, the next guy will.

 

[yeldogt]

I am still on my initial 500 gallon propane fill, with the generator exercising 10 minutes per week, multiple outages ranging from minutes to 4 days.Still have 55%. 38kw generator installed March 2018. My house is all electric 3000 sq ft.

Have you smacked the gauge recently

My old cheat sheet tells me a 38k will get 150hours at around the 75% duty cycle output w/ 1000 gallon of propane at 80% fill. So you are 1/2 that ....

You would be out of propane if you needed full output .... my new house is 5k sf and the studio is 1700sf. Not all electric ....

38k would eat too much propane for my load ....

I was factoring my duty load to eat around 2.2 gallons an hour running everything normally -- cutting back under 2. My worst case would be 4 days -- so I need 200g reserve at all times. In the winter that can get tight.

The newer generators don't need the same exercise time. That was one of the things I liked about the Cummins. It uses the starter motor to turn the engine and the alternator -- this keeps the contacts clean and the motor ready to start. One you start them in the winter -- it's the engine that has to run in order to fully warm

 

[yeldogt]

I am still on my initial 500 gallon propane fill, with the generator exercising 10 minutes per week, multiple outages ranging from minutes to 4 days.Still have 55%. 38kw generator installed March 2018. My house is all electric 3000 sq ft.

Have to check the curve -- see how cold the unit can operate. In a outage -- you would have to live with what it can produce. lock out the strips.


How do you make hot water ?

 

[jeepxj]

Have you smacked the gauge recently

My old cheat sheet tells me a 38k will get 150hours at around the 75% duty cycle output w/ 1000 gallon of propane at 80% fill. So you are 1/2 that ....

You would be out of propane if you needed full output .... my new house is 5k sf and the studio is 1700sf. Not all electric ....

38k would eat too much propane for my load ....

I was factoring my duty load to eat around 2.2 gallons an hour running everything normally -- cutting back under 2. My worst case would be 4 days -- so I need 200g reserve at all times. In the winter that can get tight.

The newer generators don't need the same exercise time. That was one of the things I liked about the Cummins. It uses the starter motor to turn the engine and the alternator -- this keeps the contacts clean and the motor ready to start. One you start them in the winter -- it's the engine that has to run in order to fully warm

thats a steady state load of 28kw.

thats wildly high for normal homes.

 

[PLANofMAN]

What about one of those Miller Trailblazer welder/generator combos? I've read that they can run two 4 person households, and they ramp up if you need more power. Cost about 5k.

Edit: nevermind. Only pushs 12,000 watts. It would run my place.

 

[petee_c]

why heat with electricity if you are bringing in propane to run a generator?

 

[jade97]

Have to check the curve -- see how cold the unit can operate. In a outage -- you would have to live with what it can produce. lock out the strips.


How do you make hot water ?

Electric water heater, Single zone heat pump for HVAC, on well & septic. Even my fireplace is electric. Also have an outdoor hot tub for the last 1.5 years.

When we are on generator power we live like normal.

 

[jade97]

why heat with electricity if you are bringing in propane to run a generator?

In my case, the wife is afraid of flames in the house. She experienced a house fire as a kid, due to a malfunctioning HVAC.

 

[NUTTSGT]

I moved this to the Lighting & Electrical section. These guys here can probably give you some really good information on load calcs and what you need.

 

[OccupantRJ]

Upgrade your heat pump to one without strips, then get a much smaller generator = save a lot of money?

Well i guess in texas the heat strips aren’t running much.

He can remove a control wire in the unit and eliminate the heat strips or part of them. I cut my shop unit back from 10k to 5 k due to the size of the preexisting shop feed circuit.

 

[yeldogt]

thats a steady state load of 28kw.

thats wildly high for normal homes.

Agree on the usage of the 38 ...


I was responding to the two people who have water cooled 38's ..... on propane you have to be careful depending on setup. Even at minimum usage they can consume a lot of propane.

For most people the 20/22k will do all they need and more -- load shedding is easy with the new ones.

Around me -- we often lose power in the summer ... typically late afternoon storms. These are fuse trips and they only last an hour (if that) -- very rare to have a few hours. I don't need all the AC units and pool pumps running.

In the winter -- that's a different situation. They are longer and the few with ice can delay emergency propane deliveries. Having that 4 day supply is important.

IMO for most people the 20/22k are the ticket -- big enough to be able to handle most houses with simple load shedding. That makes for the cheapest install -- it's expensive getting a dedicated panel installed and switching things over. The main transfer switch is often really easy to install/ retrofit

 

[dcg9381]

why heat with electricity if you are bringing in propane to run a generator?

1) I forgot when designing a house.
2) Getting propane into the air handler means cutting a lot of drywall.

 

[dcg9381]

This is a dumb question, but what's typical draw of heat strips? I see 15KW (above) - but that's 62 amps - I don't recall seeing that type of wiring running to the air handlers in my home... The heat pump compressors are all under 30A.

Just wondering if I'm doing it wrong. I have a load shed setup on the AC compressors.. Sounds like I may need one in line with heat strips... (for the 2 days per year in Texas that we use heat strips typically)

 

[theoldwizard1]

This is a dumb question, but what's typical draw of heat strips? I see 15KW (above) - but that's 62 amps.

Electric heat is 100% efficient. If the element put out 15kw of heat (51,000 BTU) it consumes 15kw of electricity !

 

[dcg9381]

I get it, I just dont remember seeing that big *** breaker somewhere.. More investigation needed.

 

[logical]

Cant answer your question

But I will say my next door neighbor just had a natural gas one installed. It starts up and runs on it’s own once a week. If I had to guess it runs for like an hour, not sure.

It’s pretty annoying, and it has to be consuming a good amount of gas. Just want you to factor that in as I’m sure propane isn’t cheap.

Mine does that but its for like 6 minutes.

Its sized slightly below bug enough to cover every single electric thing I own but has the ability to shed off the A/C and try again later if it is overloaded. That would only likely happen if I was baking pies in both my main kitchen and the basement while drying a load of laundry, microwaving a bowl of soup, blow drying my hair and running my compressor all at the same time...and I never do half of those things.

22k nat gas unit, 4000+ sq ft finish area house but just two of us living here, gas water heater but elec clothes dryer and oven(s), 3.5 ton a/c. The key is the a/c shedding module .

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