Whole house generator follow-up (fuel use)

[Wild Turkey]

Couple of years ago I posted a thread about a generator for my new house and got some good advice about size, etc.

Wife's health issues got in the way and I'm just now picking up where I was.

Looks like a 20 KW unit is what I'll need for a long-term outage (also getting advice from professional installer).

How much propane should I anticipate using per day?  House is well-insulated, 1600 sf ground floor with half of the basement occupied. LED lights, heat pump.  I anticipate turning off water heater until needed, then turning off heat pump until we're clean and starting heat pump back up.

So who has some experience in fuel consumption of similar units?  What size tank is best choice? We've got good service out here.

[Snipe Hunter]

Mine is not propane so I can't help you there. But, I run a 1500kw. 50 gallon elect water heater, well pump, heat pump and a mini-split heat pump. No issues at 1500KW. I don't shut down anything. Oven and stove-top, no problem. We don't do anything different when on the Gen.

Note: The only thing that makes a difference is when the microwave starts up so I just don't use it. The lights will dim.

20KW should be more than enough... maybe even something a little smaller if you want to burn less fuel.

[R Clark]

I have a Generac 22kW.  Spec'd propane consumption is 2 gallons per hour at 50% load and 3.6 gph at full load.

In the winter, my planning factor is 60 gallons per day of continuous use.  I monitor the level in my propane tank so that it never drops down below 30% full (that's 300 gallons in my 1,000 gallon tank).  That will run the generator for three days of continuous use while also providing propane for the furnace.  In reailty, if I had an outage going that long, I'd be in "conserve mode" and shutting down for periods of time to conserve fuel.

[R Clark]

Let me add this regarding propane tank size.

In addition to the generator, my tank provides fuel for the propane aux burner that is associated with my heat pump.  It also fuels the heat in the shop building; that's 100K BTU burner heating1100 sq ft of floor space with 12ft ceilings.  We also use propane for the kitchen cooktop, two gas fireplaces, and the patio grill.  I keep the shop at 45-50 degrees when not in use, and 65 when I'm working out there.

When we moved in, the propane tank was a 250 gallon tank and it was placed in the worst possible spot on the property.  Since it needed to be moved and I wanted a bigger tank so I could heat the shop building, I asked for a quote for a 500 gallon tank to be placed in a better spot.  The propane guy quoted the 500 gallon tank, but also said that I could have a 1,000 gallon tank for only ~$200 more.  Just like that, I had a 1,000 gallon tank.

[Wild Turkey]

Thanks for the information. Plenty to think about.

Problem is with the generator being the only propane user how can I justify a big tank?  Have to get some advice from supplier.

[Stwood_]

Big tank and have it filled, will save you money on future fillups down the road. LP always goes up in the winter, not down.

[Roly]

Thanks for the information. Plenty to think about.

Problem is with the generator being the only propane user how can I justify a big tank?  Have to get some advice from supplier.

Talk to your install or propane supplier as to what size you need for the coldest temperature outside.  As I understand it the needs more liquid surface area to convert the liquid to a gas the colder it is for a given amount of gas.   Roly

[R Clark]

Thanks for the information. Plenty to think about.

Problem is with the generator being the only propane user how can I justify a big tank?  Have to get some advice from supplier.

Apologies if I implied that bigger is always better.  I was just saying that my large tank is based on significant propane use.

If I was in your position, and the propane was only for the generator, then I think I would look back over the last five years and determine the longest continuous period of time that commercial power was out.  Find the spec'd fuel consumption for the generator you choose, and then figure out how much fuel you need on hand to power the generator for the extended power outage.  Adjust up or down based on what you're willing to live with.

I remember your previous discussion about the generator and the need to have power available 24/7 for your wife's medical circumstance.  Do you still need/want 24/7 power?.

For example, let's say that I determined that the tank would support 72 hours of generator operation, plus a reasonable buffer.  If the predicted fuel consumption is 2.5 gph, then that would be 60 gallons per day, times 3 days is 180 gallons.  Based on that, I would put in a 250 gallon tank.

Keep in mind that tanks are only filled to ~80% of stated capacity, so you would have 200 gallons in a "full" tank.

I also agree that a propane supplier or the good generator dealer can advise you and help you make a decision that's right for you.

[Snipe Hunter]

I tried to buy a tank... that was a fruitless waste of time. The only thing I could find was Chicom made tanks online. Nobody would sell me an American made tank. So, we're leasing the tank. It's 120 gal but I believe they only put in 100 gal.

It's kind of a racket. All we run off the tank is a fireplace at this point. Considering adding another regulator for a grill or maybe converting the Generator to propane. But the propane guys have to install the regulator. If they show up to fill the tank and there's a new regulator, they wont fill the tank. Also need a permit for any new appliances off the tank and a licensed gas fitter has to do the work. The tank guys wouldn't even put in the tank without seeing the permit for the fireplace plumbing. <- these were the easiest guys to deal with... and the cheapest. I got a wide range of prices for leasing a tank. Anywhere from $6 to $14 a month. No regrets at $6 a month. I poured the pad.

A Thailand or China mfg tank was in the $1200 range. That's 200 months at $6 a month. It's cheaper to lease than buy and they will do any repairs. They also garantee same day service if I buy their gas. We burned 20 gallons from basically Christmas to Christmas.

So $6.00 a month and 15 gallons in 1 year. 10ft from windows/doors or elect meter. A horizontal tank wouldn't work against the house.

[fredhargis]

I'm set up much the same way as Ray is, I have the Generac (actually a Generac with a Honeywell label) 22KW generator. My propane setup is a little different, I have the genny on a 500 gallon tank, and the house has a separate 330 gallon tank. The house tank feeds the gas cooktop and the shop heat, and when called for, the house furnace. The main heat source for the house is a ground source heat pump, in the shop it's a ceiling mounted gas furnace.. During outages (if they look like they'll be extended) I'll manually switch the furnace to gas to lighten the load on the genny. Propane suppliers vary widely across the country on what they will or will not do. My supplier does not sell tanks, but offers a "lifetime" lease that runs rounghly 1/2 the cost of the tank....that also saves slightly on the propane cost. He will also install one and charge that extra cost for propane. Other suppliers in the area will sell a tank and install it, and others will only put their own in...sometimes with an annual "underusage" charge if you don't burn a predetermined amount of LP. So you need to check around and see what's offered. Bear in mind LP tanks can only be filled to about 80% of tank capacity, and need to refilled somewhere around the 30% mark, so you don't have as much usable gas in the tank as you might think. In the 30+ years I've lived in this area, we've had one outage that went 3 1/2 days or so, and I think I've got that covered, most of them are on the order of several hours and I think there was one tahat went 13 hours +/-....so I'm comfortable with the way I'm set up. One other thing about buying your own tank. May seem obvious, but if you lease or take a suppliers tank, you can only get your LP from that supplier and are subject to whatever price they want to charge. Owningyyour tank allows you to shop around a little, though most of them offer "summer fill" discounts along with winter "pre-buy" discounts that are worth looking into.