Heatpump efficiency is measured by COP. COP goes down with temperature but at typical temperatures (where you'd use heat) is around 2.5-3.0 (ie 250 to 300% efficient). At subzero temperatures, efficiency is pretty low...............

Unless it's a GSHP.

You also have to factor in the efficiency of the gas furnace if you are trying to compare the cost of fuels. Efficiencies for new gas equipment are in the range of 80% - 98%.

The issue is the heat pump efficiency for an air sourced heat pump varies with outdoor temperature. That could mean on warm day the heat pump is less expensive to operate, but on a cold day the gas appliance is less costly. A ground source heat pump will have a higher efficiency and have less variation across outdoor temperatures. But the initial installation cost will be much higher.

"Efficiency" factors used when looking at heat production by electrical means is a completely different animal than "efficiency" of gas equipment. They're not intended to be compared as absolute numbers. The confusion is sometimes intentionally perpetrated in sales efforts, as in "This heat pump will produce heat with 300% efficiency, while that gas furnace is less than 100% efficient, it's only at 95%", Nonsense.

Electrical resistance heating is said to be 100% efficient because that's what it was defined to be. It could have be defined to be 1000% efficient, or said to have an efficiency of 10, it's an arbitrary number in an absolute sense in any event. It serves as a basis to compare one thing to another, it's a term that's relative. All electrical resistance heating is 100% efficient (by definition) but it's incredibly inefficient and expensive to use.

To say a heat pump is, for example, 300% efficient means that for a given amount of electricity, it will produce 3X more heat (in BTUs) than a resistance heater. Or, can produce the same amount of heat using only 1/3 the amount of electricity. Efficiency (COP) varies with equipment types, ambient temps (air or ground for ground source units) and sizes. It provides a means of comparison of different pieces cost to operate.

Gas appliance efficiency is different. Of the total energy contained in a unit of gas, how much of that energy as an input will be converted into the output of the equipment?

Where the relative efficiency of the choices comes into play is in computing the cost of operation in money terms. Define the number of BTUs to produce, calculate how many units of input the given type of equipment needs to produce those BTUs and cost of the input (whether electricity, natural gas, fuel oil, etc) , and you have your operating cost comparison. Nowhere in the calc is the efficiency of different types of equipment (combustion versus electrical) compared one to the other.

Many poster ask the question "What is the most efficient way to heat and cool my house"? What they are really asking is what is the most economical way to heat and cool. Electric heat is the most efficient, but in my places the most expense. On the other hand you may have a wood fired boiler where have the heat goes up the chimney which would make it only 50% energy efficient, But if you have source of inexpensive wood, it could be the most economical way to heat your house.

Mechanical efficiency is defined as the ratio of output divided by input. In the case of HVAC we want to know how much energy comes out for every unit of input energy. You pay for the energy that goes into the equipment, you want to know how much of it you get to use at the output. With this information and the cost of a unit energy you can compare different HVAC equipment.

I am curious as to where electric heat has been defined to be 100% energy efficient. There is always some energy loss between the circuit breaker panel and the electric heating elements. Some of that wiring may be inside the condition space, but some of it could be in the unheated attached garage. The resistance of 100 feet of 14 gauge wiring is 0.25 ohms. The resistance of a 1500 W electric heater is about 9,6 ohms. Doing the calculations you could get about a 2% loss in the wiring. It is a small number and not enough to have a significance when comparing HVAC equipment.

"I am curious as to where electric heat has been defined to be 100% energy efficient."

This is my understanding. It's not different than the F temperature scale where freezing is 32 degrees. It could have been set to be anything, including 0 or 400 or anything else.

The C scale set freezing at 0 and boiling of water at 100? Do those numbers mean anything in an absolute sense? No, they're relative and are used in formulae. Freezing could have been 100 and boiling 500. If they were defined differently, math would be adjusted accordingly. If you set freezing at 0 and boiling at 100 and want to have 100 equal steps to get from one to the other, then you have the definition of what 1 C degree is. Does it mean anything in an absolute sense? No to that one too.

I believe that what is meant by electric heat is 100% efficient is that whatever power is dissipated through the heating element, 100% of it is dissipated as heat, unlike incandescent light bulbs for instance where most of the energy is released as heat, not light.

Hi, mtvhike,

Heat pump manufacturers provide different measures of heat pump "efficiency" depending on whether the unit is operating in cooling or heating mode. In cooling mode, it is expressed as a seasonal energy efficiency ratio (SEER) which is calculated across the seasonal range of outdoor temperatures. It's the ratio of total heat removed in the cooling season (BTUs) to electrical energy consumed (watt-hours.) For heating mode, it's expressed as a heating seasonal performance factor (HSPF) which is the ratio of the heat produced (BTUs) to electrical energy consumed (watt-hours.) DOE's minimum SEER rating for heat pumps is 14 and their minimum HSPF is 8.2

"I am curious as to where electric heat has been defined to be 100% energy efficient."

For every 1 btu in, there is 1 btu out. Zero waste. Where as gas can't say that because of flue gases. Heat escapes up the flue with those waste gases, of which you don't have with electric heat.

You know assuming your system is pumping the heat into your home. It's true and it sounds good for the general public. But electric heat is more expensive.

Without going too far into the weeds:

5KW of heat costs 20amps of power. Smaller homes may need 10KW in my area. Some larger homes as much as 20KW. So if you're one of these larger homes 4x 20 = 80 amps of power (cost) --- with 80 amps burning the meter is saying "yippee-- spinning like mad" --- unless you have a smart meter then there's no spinning.

80 amps versus what a typical AC/ Heat pump would run. A single stage 4 ton / 5ton heat pump is going to cost you (depending on efficiency of the unit) some where in the realm of 15 amps to 20 amps or so.

Assuming you never need to run defrost, etc. You can see that if the heat pump only ever pulls 20 amps, that 60 amps less than strip heat. 1/4th the cost. Once you dip below 35F, this degrades as defrost comes at an expense.

The coming of the Inverter heat pump. Heating performance is even better. Heat capable down to 5F, amp draws insanely low at warmer / mild conditions. Total amps when running in slow mode 4-5 amps.

Compared to 80 amps. With inverter ramped around 15 amps. The inverter costs more up front. Costs more to repair it. But as electric costs more and more you can see clearly where it's going.

I have an AC inverter at my house. Electric bill for AC is estimated at less than $80 @ around 9.6 cents per KWH. That's a savings of over $100 compared to old single stage 14 SEER AC unit.

I service the Katy, Texas area.

What is an Inverter AC? Watch the video....

So if you're one of these larger homes 4x 20 = 80 amps of power (cost) --- with 80 amps burning the meter is saying "yippee-- spinning like mad"

C'mon, Austin. Amperage is a measure of electrical current--not power. Power is measured in kW not amps, and electrical energy is sold in kWh--not kW. When you use the wrong terms you add confusion, not clarity. At least get the simple stuff right.

C'mon, Austin. Amperage is a measure of electrical current--not power. Power is measured in kW not amps.

C'mon Charles,

The higher the amperage the more it cost you "man". --- I said--- without trying to go to far into the weeds... man.

If you're running 80 amp appliance vs. 15 amp appliance which would cost more to operate?

"If you're running 80 amp appliance vs. 15 amp appliance which would cost more to operate?"

I'm not looking to beat anyone one up here as I enjoy the great content both you guys contribute but the above statement is dependant on the voltage that amperage ( and vice versa) is inextricably linked to when power is calculated.

I know that you know that Austin, this is just for the benifit of those that don't.

SR

All HVAC appliances are machines. All machines have losses. If they did not have losses then you could build a perpetual motion machine. So far many have tried but no one has been able to make one.

There is no harm in saying for comparison purposes that electric heating is 100% efficient. I use a spreadsheet to do the calculations to generate the costs for 100K BTUs for using various fuels. I use 100% efficiency for electric heating. The costs are usually so high that if I did to include a small loss it was still be much larger than the other fuels. It is not worth arguing about it.

Lennox is claiming some of their gas furnaces have an efficiency of 98.7%. That is a 1.3% difference from 100% efficiency. Most people's gas rates have a bigger monthly change than 1.3%.

@Austin Air Companie,

Get the simple stuff right if you want folks to consider you credible with regard to bigger stuff. And with regard to bigger stuff, you never answered the question "I am curious as to where electric heat has been defined to be 100% energy efficient." Instead, you switched units to BTU (we don't use BTUs with electrical calculations) and simply proclaimed For every 1 btu in, there is 1 btu out. Zero waste." Then you launched into your usual commercial for inverter heat pumps.

The first law of thermodynamics establishes that all work can be converted to heat, but not all heat can be converted to work. With respect to electricity, consider an electric hot water heater that is perfectly insulated (no heat losses.) All of the work input (in the form of electrical energy) is converted into heat so it's considered 100% efficient.

One poster on this thread asked about voltage drop from the panel, etc. Good question because it makes the point that the efficiency of a system depends on where you draw the system boundaries. My water heater example draws the boundaries right at the hot water heater and considered the system to be perfectly insulated. If you drew the boundaries at the home's electrical panel--or worse yet, the power generating plant--you would need to consider the transmission losses when evaluating the system's efficiency. You'd also need to consider the heat losses from the hot water heater since in the real world, it's never perfectly insulated.

Let's go back to heat pumps. The efficiency of a heat pump is measured either in SEER or HSPF depending on whether it's in cooling or heating mode. But what really matters is the efficiency of the complete HVAC system. A very-efficient heat pump coupled with a duct work system designed by a hack or retrofitted over time by a number of hacks isn't going to be as efficient a system as one with properly designed ductwork. Proper design is important in order to achieve the established design objectives. Houzzers will be well served to ensure the design professionals they select--from architects to engineers to HVAC designers are, in fact, competent designers and not just good salespeople.

@fsq4cw,

I can only imagine you're referring to the entertainment value. I think I know how Bud Abbott felt always playing straight man to Costello.

Sorry I lead so many of you into a rabbit hole. I'm assuming that when comparing different kinds of heaters, all units of energy are converted to be equivalent. As others have said, resistance heat is 100% efficient, because any losses in the system are ultimately converted to heat..

There’s not been any discussion on the advantages that a GSHP has over an ASHP in cooling, just in heating. They do exist.

I assume a GSHP has a higher COP than an ASHP, but the capital cost is much greater.

Well, given that the ground 8'-12' deep rarely get down to freezing, yes, GSHP will have a higher COP at 0 degrees (C) air temperature than an ASHP operating at the same air temperature. And yes, a GSHP will cost 5-10 times as much as an ASHP using backup strips.

Yes, it’s a given that a GSHP delivers a higher COP than an ASHP. Yes, it’s a given that installation costs are usually much higher. But, the title of the thread is Heat Pump ”Efficiency” and no one has mentioned that a GSHP is more efficient at cooling than an ASHP. In some areas a home owner spends more cooling than heating.

"no one has mentioned that a GSHP is more efficient at cooling than an ASHP"

I haven't seen any comparative data in heating mode. It makes theoretical sense that GSHP would be more efficient at cooling but the question is how much more efficient(?)

An ASHP’s efficiency in transfering heat from the house decreases as the outside air warms. This means that an ASHP is least efficient at the hotest temperatures when it’s most needed. Whereas, a GSHP transfers heat to a much cooler ground temperature maintaining its higher efficiency.

Comparison is complicated because most ASHPs use SEER and GSHPs use EER. It’s my understanding that an EER will translate to a higher SEER but I’m not an HVAC guy.

"This means that an ASHP is least efficient at the hotest temperatures when it’s most needed."

You mean as on a hot day when its cooling operation is, in theory, the same as a standard air conditioning system? Is that a problem?

The thing is, if ground source systems were so whizbang and economical, why is it so frequently the case that the payback point is so many years out, if at all? Unless buying or building a home one expects to own for decades, it can lead to wasted money.

They do have their place, when the most expensive means of heating are the only alternatives, but even then, not always.

Air source heat pumps have both SEER and EER ratings. You can compare the efficiency to a ground source system.

Sorry I lead so many of you into a rabbit hole. I'm assuming that when comparing different kinds of heaters, all units of energy are converted to be equivalent. As others have said, resistance heat is 100% efficient, because any losses in the system are ultimately converted to heat..

LOL. You've lost 99% of the people out there with this thread as it stands. I have to have understanding to simplify it as much as possible. There's things that matter, there's things that are just a "new argument" to sell something of which most won't need or want. (pre-existing structure that may only be lived in 5, 10, 15 years.) Context of what you want to do and for how long.

Money & Sales is a "two way street" -- let's spend money on crap we don't need, engineers we don't need to converse with when it comes to a pre-existing structure.

Lets get the architect involved to engineers to HVAC design people. I believe Mr. Ross has quoted the entry fee of $2000 before, I'm sure he'll correct me if I am wrong. That $2000 is before any real work gets done. Mr. Ross isn't going to do the actual work, he's going to shuffle that off to his "trade partner". IE subcontractor, GC all of which are commodities to him. (He tells them what to do, hopefully that translation isn't lost.) The first sign of "house of cards" trouble, the HVAC contractor is the first to go... ask me how I know?

Anyone can do HVAC, you have to live with the result. That $2000 fee isn't going to do anything for you then. That being said: if the structure is being built... then of course you need architect, structural engineers and a myriad of sub contractors and GC's. If the structure is pre-existing? Right tool, right job. Anyone can gold plate something. If you have more money then sense go for it. For me it changes what? "NOTHING". big fat goose egg.

I'm not looking to beat anyone one up here as I enjoy the great content both you guys contribute but the above statement is dependant on the voltage that amperage ( and vice versa) is inextricably linked to when power is calculated.

True. However it's common knowledge that AC condenser operates at 240 volts / AH with strip heat is also 240 volts.

Now you know "WHY" I said.... long, long ago: WITHOUT GOING TO FAR INTO THE WEEDS, man.

No matter the argument, there is always the counter argument. Something Mr. Ross has yet to realize. Much of what I do here... is play "devil's advocate"... the devil as it were is in the 'details'.

click to enlarge...

I service the Katy, Texas area.

I mean this:

“In the summer months, geothermal heat pumps deliver heat to the same relatively cool soil (or groundwater) rather than delivering it to the hot outside air. As a result, the heat is pumped over a larger temperature difference with a geothermal heat pump and this leads to higher efficiency and lower energy use. Goswami, Yogi D., Kreith, Frank, Johnson, Katherine (2008), p. 9-7.]”

And, I’m in total agreement that initial installation costs are high. It just seems that most discussion I’ve read here is about heating not cooling. In a high heat, high humidity environment the monthly difference in electrical useage between the two systems is more pronounced.

The original author of the post asked how the costs of gas, electic, and heat pump heating can be compared given each have different efficiency ratings and fuel costs. The cost comparion calculations are the same if the heat pump is air source is air, earth, or water.

Calculating costs for cooling is more complicated. It is an interesting topic worth starting as a new posting.

I guess I led you astray because I'm ONLY concerned with heating.

@sktn77a, you mentioned backup strips. Are you mentioning them because an ASHP would require resistance backup strips but a GSHP wouldn't?

Correct (provided that the ground coils are sufficiently deep that they wouldn't go below ~50 degrees).

If I were in your shoes, I'd answer the question with a calculation or two.

Start with an estimate or guess of how many years you expect to live in this house full time. Get bids for acquisition/installation costs for the different types of equipment you have to choose from. Load calculations and equipment performance stats should help you estimate energy input usage figures, it's okay to round up a bit, to project operating costs for each type of equipment over that period of time. Using current prices should be fine (you're looking for relative numbers as between your choices, not absolute ones).

Make the decision based on total costs differences between the alternative system choices that will have the performance you want. I don't think any more than that is needed. This isn't an engineering or environmental experiment, it's a buyer's choice of what to buy.

Assume that should the house be sold, prospective buyers won't care a bit about what kind of equipment it has. Different types of equipment won't increment or decrement a house's value appreciably. The expectation is usually that the HVAC equipment works conveniently as expected or that it can be put into a condition to do so. Usually nothing more

Good luck.

And provided the GSHP is properly sized for the home's heating requirements.

@Charles Ross Homes, that would be something wouldn’t it! Pay that much for a system and find out it’s undersized!

This is all purely hypothetical - I don't plan to move, and most of my electricity is generated by solar panels. The most I'm considering is adding an ASHP to provide some cooling, (for the few days a year it's over 90) and, as a bonus, cover some of my electricity usage, for when I get a fully electric car (or two)!

Perfect.

@Austin Air Companie,

Get the simple stuff right if you want folks to consider you credible with regard to bigger stuff. And with regard to bigger stuff, you never answered the question "I am curious as to where electric heat has been defined to be 100% energy efficient." Instead, you switched units to BTU (we don't use BTUs with electrical calculations) and simply proclaimed For every 1 btu in, there is 1 btu out. Zero waste." Then you launched into your usual commercial for inverter heat pumps.

1kw = 3,412 BTU's per hour (heat produced). There is no exhaust vent on electric furnace. 1 btu in energy spent or 1/3412th of a KW if you prefer, there is 1 btu of heat out.

There is exhaust on gas furnace = waste. (however, gas is cheaper than electricity in most areas) So are you talking efficiency or $$$?

oops time to form a "new" argument, Mr. Ross.

How much more energy efficient is an inverter heat pump compared to a regular run of the mill heat pump?

What is the title of this thread?

Answer: about 50% more efficient than typical on or off heat pump. (single speed beater)

ANYONE can do HVAC --- you have to live with the result. I service the Katy, Texas area.

Your last post addresses my initial point very well; thank you.

Your last post addresses my initial point very well; thank you.

You're welcome, mtvhike.