KWH of 1 gal of gasoline.

This means to me looking at the numbers if  was cold, I would get more heat out of 1 gallon of gas by burning it then I would get from running a generator then running a heater with that generator......

next question i have is how do they determine the BTU of gasoline?      Do they burn the gasoline and record the heat put off?

Paul Stockton wrote:Run the generator inside the house and try to recapture heat from the exhaust before venting the exhaust outside....  You'll get much closer to your target numbers and a big headache.

David Baillie wrote:When the last house was offgrid I had a 2kw inverter generator running on propane in the garage. That model had a plate with bolt holes on the exhaust exit pipe. I had a long length of aluminum flexible duct attached to it. It ran in the garage and out a hole. It did a great job heating the garage. Ultimately I did not incorporate it in the new place as it was too much fiddling. I figured if you incorporated the generator, got as much easy heat out of the exhaust as possible, you fed a good mini split suitable for cold climates with the power you could beat the burning straight gasoline heat value but at a huge technological cost... The advantage would you could incorporate solar to run the heat pump.

Steve Zoma wrote:Oh sure, while energy can neither be created nor destroyed, there are conversions losses.

25 percent of an engine goes to heat output instead of mechanical power

It’s why engine name good co or tri generation. You can pull the heat out if the engine for stacking functions.

Mart Hale wrote:

Steve Zoma wrote:Oh sure, while energy can neither be created nor destroyed, there are conversions losses.

25 percent of an engine goes to heat output instead of mechanical power

It’s why engine name good co or tri generation. You can pull the heat out if the engine for stacking functions.

Yes, I am looking at either stacking functions, or buying alcohol and burning it inside the home as I would get more BTU per dollar than the gasoline would give me running the generator.      4 KWH of heat out of a total of 36 KWH  is horrible amount of energy loss from 1 gal of gasoline.


Cooking inside with alcohol, or even using it to distill more alcohol seems like a much better way to go.

Mart Hale wrote:

Steve Zoma wrote:Oh sure, while energy can neither be created nor destroyed, there are conversions losses.

25 percent of an engine goes to heat output instead of mechanical power

It’s why engine name good co or tri generation. You can pull the heat out if the engine for stacking functions.

Yes, I am looking at either stacking functions, or buying alcohol and burning it inside the home as I would get more BTU per dollar than the gasoline would give me running the generator.      4 KWH of heat out of a total of 36 KWH  is horrible amount of energy loss from 1 gal of gasoline.


Cooking inside with alcohol, or even using it to distill more alcohol seems like a much better way to go.

David Baillie wrote:

Mart Hale wrote:

Steve Zoma wrote:Oh sure, while energy can neither be created nor destroyed, there are conversions losses.

My problem here with auxiliary heat is that I would need something vented to the outside as direct burning inside would be a problem in our airtight house. The humidity would give the hrv fits let alone the air exchange necessary to offset emissions. I plan on going the small heat pump route for auxiliary heat if necessary. Solar for the bulk of electrics and grid for the rest. I'm done with charcoal powered generators unless the world turns to poop but they are an option. Where is the alcohol coming from?
Cheers, David Baillie

Yeah, I am starting to realize a heat pump gives you 2 heat units for 1 unit of electricity energy ( provided the temp on the outside is decent )...    

Alcohol could be purchased or grown from sugar beets, or harvested from certain palm trees here in Florida.     I am always weighing the costs of alternatives, and alcohol burners is safely used on ships...

Mart Hale wrote:>>I'm going to have to look into alcohol a little closer. It's a cleaner burn then I at first thought. There is still the humidity though. Thank you! A ??>>great rabbit hole to explore!

David Baillie wrote:

Mart Hale wrote:>>I'm going to have to look into alcohol a little closer. It's a cleaner burn then I at first thought. There is still the humidity though. Thank you! A ??>>great rabbit hole to explore!

Yeah, I have the book "Alchol can be a gas"    I was amazed to find out Brazil went to alcohol to power their cars, and the first model T ran on alcohol.

Nick Williams wrote:Yeah, gasoline engines aren't terribly efficient to begin with. A really decent gasoline engine is about 35% thermally efficient, I'd hazard it's probably closer to 20% for a little carbureted small engine like you get in a generator. And then there's energy losses in the generator head, energy losses in the wiring, energy losses in the charge controller, etc. Every time you knock a few extra percent off, until you get pretty terrible recovery.

To answer your question of how the energy content is determined, it's just like how you determine the calorie content of food. A small sample is placed in a water jacketed container (bomb calorimeter) along with an excess of pure oxygen, the sample is ignited and the change of the temperature of the water is recorded. There's some additional nuance for heating fuels in that there's two ways to report it, higher heating value and lower heating value depending on whether or not the resulting water of combustion is condensed, but that's not terribly important to the discussion.

I would absolutely not suggest any sort of heat recovery system from exposed exhaust piping. It works great, until it doesn't, because a hole corroded in the exhaust, or it got knocked loose by the dog, or whatever, and that's a great way to wake up dead. If you have a liquid cooled generator (there are SOME out there, but they aren't terribly common), running the coolant through a radiator in the living space is a safe and relatively easy way to capture waste heat.

If you're wanting backup heat with a hydrocarbon, I'd consider taking a look at some of the chinese diesel heaters out there that are so popular among the vanlife community. Can be run for quite a while on a 12 volt battery just sipping diesel. Keep meaning to pick one up and build a window insert so I can have an extra extra source of heat in case of power outage...

Mart Hale wrote:
So pure oxygen is added to the fuel to  get the most complete burn......      Interesting, we don't do that in real life unless you are at nasa burning fuel...

Mart Hale wrote:
It does bring up more questions as when we burn gasoline why do we not add oxygen to it to get a more complete burn?       Or for that matter why not add it to alcohol  to also get a more complete burn?        I guess as I think about it perhaps the steel would melt at the high intense heat, would need special materials like they use in rockets,  and would have a greater potential of exploding.

Mart Hale wrote:

Paul Stockton wrote:Run the generator inside the house and try to recapture heat from the exhaust before venting the exhaust outside....  You'll get much closer to your target numbers and a big headache.

Yeah not a good idea, CO2 can kill if not vented properly.    but still the amount of heat generated that is wasted catches my attention.       I did not one guys solution was to run a longer exhaust pipe  then  run it outside after the heat was lower from the pipe...        

Paul Stockton wrote:

Mart Hale wrote:

Paul Stockton wrote:Run the generator inside the house and try to recapture heat from the exhaust before venting the exhaust outside....  You'll get much closer to your target numbers and a big headache.

Yeah not a good idea, CO2 can kill if not vented properly.    but still the amount of heat generated that is wasted catches my attention.       I did not one guys solution was to run a longer exhaust pipe  then  run it outside after the heat was lower from the pipe...        

Description is to illustrate waste heat off an air cooled engine
head and exhaust is (energy) lost btu.  And then consider the mechanical energy lost in the rotation of engine and generator friction losses.  Unless one can harness/recoup these losses, one must accept those losses.
So, recapturing some waste heat can be practical, there are practical limits.
A water cooled diesel generator would be better if you exploited the radiator and tried to recover exhaust heat.
Diesel engines produce much less CO than gasoline engines.

S Bengi wrote:Engines have an efficiency of only 1/4 aka 25%.
Then the engine has to spin the generator to make electricity and then it has to be rectified to less than 5% distortion, so in the end we only get 1/6.
Then if we use it to charge a battery, their is more lost, and when we take the energy out of the battery there is more lost again. To the point where only 1/10 of the original energy is recovered

Steve Zoma wrote:I ran into this once when I lost power for 9 consecutive days and my generator ran to provide power for the house. It seemed like such a waste, 25% of the fuel I was consuming was making heat that was going out the radiator. I have radiant floor heat, so why not just plumb the coolant lines from the engine into a pipe that goes into the radiant floor heating system? It does not care what makes the water hot, just that it has hot water. A simple circulating pump would keep the water moving to allow the engine to stay at the proper temperature.

While it is possible, it would be expensive. It has to do with the frequency of electricity and power curves of diesel engines.

In order to get 60 cycles per second frequency (also called hertz), a generator has to turn at a certain RPM. It is very unforgiven; even 1 rpm off can throw off the frequency from 60 cycles per second, to 59 cycles per second, and that causes burn-out of electric motors and will slow clocks in the house. To get that means an engine has to be run at a certain RPM. It is pretty high, so I am making maximum horsepower out of the engine which in turn is making more kilowatts than what my house is consuming for power.

And that right there is the rub.

While it is true my little engine is making 28,000 btus per hour just in heat out of its radiator, it is making far more excess energy out of the generator. Rather than build an elaborate system to capture the radiator heat (co-generation), why not just plug in electric space heaters and use the excess electricity to heat my house? It costs me the sameamount of money (diesel fuel) to produce 8 KW's as it does 20 KW's, so why not make heat with those extra KW's?

David Baillie wrote:

Steve Zoma wrote:I ran into this once when I lost power for 9 consecutive days and my generator ran to provide power for the house. It seemed like such a waste, 25% of the fuel I was consuming was making heat that was going out the radiator. I have radiant floor heat, so why not just plumb the coolant lines from the engine into a pipe that goes into the radiant floor heating system? It does not care what makes the water hot, just that it has hot water. A simple circulating pump would keep the water moving to allow the engine to stay at the proper temperature.

While it is possible, it would be expensive. It has to do with the frequency of electricity and power curves of diesel engines.

In order to get 60 cycles per second frequency (also called hertz), a generator has to turn at a certain RPM. It is very unforgiven; even 1 rpm off can throw off the frequency from 60 cycles per second, to 59 cycles per second, and that causes burn-out of electric motors and will slow clocks in the house. To get that means an engine has to be run at a certain RPM. It is pretty high, so I am making maximum horsepower out of the engine which in turn is making more kilowatts than what my house is consuming for power.

And that right there is the rub.

While it is true my little engine is making 28,000 btus per hour just in heat out of its radiator, it is making far more excess energy out of the generator. Rather than build an elaborate system to capture the radiator heat (co-generation), why not just plug in electric space heaters and use the excess electricity to heat my house? It costs me the sameamount of money (diesel fuel) to produce 8 KW's as it does 20 KW's, so why not make heat with those extra KW's?

the inverter generators go a long way to maximizing your KwHr per gallon numbers. They rev down and up to match your consumption and do not need to maintain a set rpm to produce perfect power. Lately I've been playing with a 1200 watt generator non inverter type charging a battery with an iota charger. Producing 40 amps at 24 volts. I'm finding I get maximum efficiency this way as the load stays consistent and the generator runs at it's most efficient wattage. I have thought I could pair it up to a radiant floor radiator enclosed in a metal box to act as a cheap heat exchanger... It's hard to justify though as there are so many projects to do.

David Baillie wrote:The inverter generators go a long way to maximizing your KwHr per gallon numbers. They rev down and up to match your consumption and do not need to maintain a set rpm to produce perfect power. Lately I've been playing with a 1200 watt generator non inverter type charging a battery with an iota charger. Producing 40 amps at 24 volts. I'm finding I get maximum efficiency this way as the load stays consistent and the generator runs at it's most efficient wattage. I have thought I could pair it up to a radiant floor radiator enclosed in a metal box to act as a cheap heat exchanger... It's hard to justify though as there are so many projects to do.

Steve Zoma wrote:

David Baillie wrote:The inverter generators go a long way to maximizing your KwHr per gallon numbers. They rev down and up to match your consumption and do not need to maintain a set rpm to produce perfect power. Lately I've been playing with a 1200 watt generator non inverter type charging a battery with an iota charger. Producing 40 amps at 24 volts. I'm finding I get maximum efficiency this way as the load stays consistent and the generator runs at it's most efficient wattage. I have thought I could pair it up to a radiant floor radiator enclosed in a metal box to act as a cheap heat exchanger... It's hard to justify though as there are so many projects to do.

That is true, but they also come with a potentially huge price; they are not true sine wave generators. The problem with this is, it is really hard on AC motors, and on electronic equipment. Unfortunately, they are the most expensive appliances in your home. Just as an example, blow your motor on your submersible water pump and you are spending $2000 for a new pump and piping, and the labor of hauling it up in the middle of the winter from 200 feet. It is not much of a bargain in that respect.

Quality power has to do with frequency (hertz), but also rotating mass, governor controls and synchronization. Basically, as loads in the house go up and down, there needs to be enough rotational mass to keep the generator spinning like a huge flywheel. Without a governor that can quickly respond and apply power though, that spinning reserve will dwindle and cause a lack of frequency. It does not take much, just a few tenths of a percentage too low can cause a brown-out; a much more expensive situation than a black out.

They are cheaper to operate, and "efficient", but only so far. They do not provide quality power since the microprocessors can only mimic the true sine wave to some degree.

I will add a caveat here: all these issues plague the grid as well.

David Baillie wrote:I tend to agree with you. Having a large full speed generator for large inductive loads is great.fridges don't seem to mind the inverter generators and most well pumps are 220 while most inverter generators are 110... Most home loads and the charger functions on home inverters don't seem to be affected.  Personally I've been rethinking the large generator/ inverter charger scenario that is the norm these days in off grid charging. I find purpose sized generators and chargers are much more efficient cost wise and fuel wise. I prefer letting the home inverter do the heavy lifting and a dedicated generator/ charger do the battery charging. We are slipping away from the OP it seems as happens so often...

John F Dean wrote:Hi Steve,

I was about to question the mega watts ….then I remembered where you work.

Steve Zoma wrote:Oh sure, while energy can neither be created nor destroyed, there are conversions losses.

25 percent of an engine goes to heat output instead of mechanical power