Electric Versus Natural Gas

Kevin_in_Denver_2

100% of the energy consumed by the fan ends up as heat in the air.

Ron Reeland

Electric Versus Natural Gas

Hi: I am attempting to compare the cost of hot air natural gas with hot air electric resistance heat.

My last gas bill indicates that one therm cost $1.007, including "delivery charge", taxes, etc.
My last electric bill indicates one kilowatt hour cost$.07635.

A conversion book shows a therm equals 100,000 BTU.
One kilowatt hour equals 3409.5 BTU or 29.33 Kilowatt hours equal 100,000 BTU.

A little multiplication shows that the cost for 100,000 BTU of electric heat would be $2.24 or more than double the natural gas cost.

Is the conversion to BTU a realistic method to compare costs?

If not, what method can a person use?

Thanks A Lot,
Ron

Dave_4

You do have to factor in the comparative efficiency of the fuel (electric resistance is 100%, natural gas furnace generally between 80% - 90%) but given those rates, gas will prove a significantly less expensive fuel.

In the vast majority of cases, electricity resistance is the most expensive way to heat.

Depending on your climate however an electric heat pump be less expensive at those rates--it will all depend on how much "backup" electric resistance is required.

Don't forget that energy markets are highly volatile at present and it's hard to tell what's going to happen. If history holds true, natural gas will prove to be less expensive over time. If utility companies have their way, rates for ALL fuels will be in near parity on a btu and weather basis as adjusted for "typical" efficiency.

Perry_3

A couple of factors missing...

Ron:

Actually, electric can make sense in some situations.

You are missing two factors. The natural gas furnace does not operate at 100% efficiency. More likely it is operating at somewhere between 50% and 80% (even 95% efficient boilers do not really operate there - those are peak available efficiencies if everything works out all of the time).

So what you need to do is take your therms and devide it by the real furnace or boiler efficiency (and not the nameplate efficiency).

So your $1/per therm gas might easily be $1.50 to $2.00 per heat in the house therm.

Electric is almost always 99% efficient - so it is easy to consider it at 100%.

So, depending on what your local long term nutural gas, elctric rates, and your actual average furnace efficiency (not nameplate efficiency) - electric might be cheaper than natural gas in some areas of the US.

The other factor you need to look at is installation and maintenance cost. Electric baseboard and electric hot water is cheap to install and needs almost no maintenance. Also, tends to be cheap to replace. This could be huge savings up front - and long term on a new system.

However, there are restrictions in many places about installing significant electric heating.

In many places in the US natural gas is the more economical choice just on fuel const. But not everwhere.

Also, If all I needed was a small system, electric may make sense based only on the difference in installation and maintenance cost.

Personally, if I had one of the really small houses in town (we have some 500 sq ft houses) - or a really well insulated new one... I'd probably just go electric.

Hope that helps,

Perry
Homeowner

rumn8r

what about

newer ground source heat pumps with efficiencies of 400-500% compared to electric resistance?

Perry_3

A good choice for many applications

Ground source heat pumps would be a good choice for many applications - especially new construction.

Still, there are places where it becomes very costly - if not impossible to install.

In my case, I wanted to retrofit my house to ground source heat pumps.... but could not find anyone producing a standard unit that would produce 140 F water that my existing cast iron baseboard needs when it gets cold out. Most companies stop at 120 F - and they don't even want to go there if they can avoid it. I was told that a more reasonable maximum was 100 F.

The other thing to be aware of is undersized and/or shallow fields... that suck to much heat out of the ground over a few years than nature can recover. Adequately sized heat source fields cost $$$$$; and it is unfortunate - but true that some contractors cut their bid by reducing field size or debth...

So, yes something to consider - and it may work in many cases. But, pay attention to installation cost for a good system.

Concerning those several "samll" houses that exist in town. Some of them have almost no yard and their is more driveway than grass in one case where someone built a garage later that is bigger than the house. I doubt it would be cost effective to tear up and replace a cement driveway in order to drill holes for a ground loop heat pump.

Perry

Wayco Wayne_2

Dual Fuel

is a smart thing to do depending of course on the utility rates you are living under. This thread is timely since I just got my gas and electric bill and just switched to dual fuel this Winter. Dual Fuel is a heating system that uses an air source heat pump for heating when the outside temps are 35 and above, and switching to a gas, or oil back up below 35 degrees outside. For my system I went a little further. I keep the heat pump going all the time, but am using a hot water coil downstream from the air handler whose hot water source is a Munchkin mod con boiler. I have a supply sensor in the supply air that works to keep the supply air temps between 115 and 120 degrees. I am payiing aprrox. .10 per KWh, and 1.95 per therm for nat gas. I saved 278 dollars on my gas bill for the last month while my electric bill went up 150. Total savings 120 per month. However as was mentioned, utility prices are volitile and my electrical supplier, is locked into their rates until July of 2009 at which point I expect a significant increase in KW cost. WW

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Perry_3

Off Peak \"Thermal Mass\" Electric heat

This may be available in some areas.

In the early 1990's I installed as part of rent on a place I lived an "off peak" thermal mass electric heat system.

This consisted of a series of cabnits filled with bricks that were electrical resistant heated at night at a significantly reduced electric rate, with each cabinet having a thermostatic control for the room it was in - with the thermostate controlling a fan that circulated room air through the heated bricks. The system I installed was made in Sweedan - and was sold by the utility company to people willing to install them at a very reasonable rate.

The utiltiy upgraded the transformer, ran heavier lines, and donated a double meeter panel for the project, and a special switch that turned on and off the off peak electrical panel.

I installed a new - dedicated and locked by the utility - 200 Amp electrical panel, and 5 or 6 themal mass heating units. Main wiring for the thermal mass units was probably 8 guage (3 wire), and the thermostates were 120V.

If available it is likely that electric heat will be energy cost comparable - or even cheaper than - natural gas.

The key here was that the utilities typically have a huge load imballance between day and night service. It saves them money in certain cases to install off peak load. The utility set up about a thousand such off peak heating systems in a 2 year period.

While your local electric utility may not have a formal advertised program to add a bunch of off peak load... It might be worthwhile to inquire if they have special off peak rates for people who do - and if they support the installation of such a system.

Of course - it takes some work to install, and you have to accept warm radiator cabinets in the rooms.

Oh, and the system worked well.

Perry

rumn8r

That is

similar to what I am now considering. I currently pay $0.10 per kwh for electric which increased 20% over the last 4 years and $0.97 per ccf natural gas which increased 40% over the last 4 years. This works out to $0.0296 /kbtu for electric resistance heat and ~$0.0106 /kbtu for natural gas at 92% annual efficiency (if possible). However, newer ground source heat pumps (GSHP) have efficiencies up to 5X that of electric heat bringing the cost down to $0.006 /kbtu or about 56% of a highly efficent ModCon boiler. The problem is that I require more heat than GSHP can deliver without oversizing (and short-cycling) cooling capacity (they generally provide more cooling btu than heating). Because electric resistance is not a cost effective supplemental heat source, I am considering a ModCon boiler as a supplemental heat source by putting an oversized coil in the airhandlers of the GSHP units. I would control it similar to WW above turning on the circulation pump to the hydrocoil as a second (or third) heat stage. I would size the hydrocoil so that the ModCon could provide all the heat on design day in the unlikely event that electric rates increase more quickly than natural gas.

rumn8r

Perry, I am trying

to find out more about ground loops and their efficiency over time and I realize that this is not the forum (or thread) for this but I found your comment interesting: "undersized and/or shallow fields... that suck to much heat out of the ground over a few years than nature can recover" I can see this happening over a heating season but do you really think it happens over years, especially if the loop is too shallow? Do you think vertical wells recoved better than horizontal loops?

rumn8r

Actually,

I didn't think of controlling the supplemental heat from the boiler-hydrocoil exactly the way WW has. Sensors in the supply duct to increase temperature will prevent the draft problem that heat pumps have because of blowing air close to body temperature; I like that idea.

Perry_3

Yes it can - and it has happened

Depletion of the natural thermal mass has occured, and there are a number of such stories out there. It typically takes 3 to 5 years.

I spent years researching the subject because that is what I wanted to install (unfortunately getting to 140 F water was not feasable without a truely custom system and low efficiency).

How it happens is that lets say that the "average" ground temperature is 57 F. During the first winter you pull it down to 50 F. It recovers to 55 F during the summer. The next winter you pull it down to 48 F. During the summer it recovers back to 53 F. The next winter is really cold, and you pull it down to 43 F (where the equipment is really struggling), and spring is late and summer cold and it only recovers to 48 F. The next winter you pull it down to about 43 F and your system can no longer keep up with your house by the middle of the winter... and then it pulls the ground temperature down to about 41 where the system overloads and dies. It will take the ground aproximately 4 to 5 years with no heat extraction to recover to the original 57 F.

This scenerio has happened on both shallow buried tubing, and well holes. Actually, there were cases where the shallow buried tubing pulled it down to near freezing as the frost line went deeper than normal because the ground under it was colder than normal.

You must actually have an "oversized" field where you do not remove more heat in a winter than what can recover in the summer.

It has been about 5 years since I did that research, and with the dying of my previous computer I lost a lot of link information to various sites. Anything that I downloaded and saved was not lost.

So the information is out there and findable; however, you will not find it on the sites that tell of their "success" stories.

I also note that the industry in general learned a few lessons on sizing of fields - and a good designer will not let this happen today. However, what I planned on doing to the people designing my system was to have an extra 25%+ of well holes drilled beyond what they calculated. Better safe than sorry.

Perry

rumn8r

So,

sizing for air conditioning and using a boiler to make up the difference between heat needed and heat provided by the GSHP, this should be much less of a problem, particularly because the ground will be heated in the summer, right?

jp_2

not sure ele heat 99% eff

you need to factor in the fan load also.

then you do not want the fan coming on until the unit is 'warm' then you do not want the fan running until the unit is at room temp?

unless I'm wrong this sounds like the operation of a FHA furnace?

so 99% efficiency does not sound correct?

i guess if the heating load is so large that it dwarfs the fan load then it makes sense.

nick_7

Another advantage of electric heat is no combustion in the home, no CO worries.

Dale

another possible option

Another thing to look at is off peak electric rates and time of use rates. Off peak is for water and space heating, if you allow the elect company, popular with co ops, to shut you off when they are nearing a peak when they would need to buy expensive elect. you save about 40%. This is no problem in a well insulated house. Then, time of use. here the utility installs a special meter where you save a lot at night and at other times during the day when elect use is lower. A friend of mine does this and saves with a timer that only allows his elect water heater to run when it's cheap to do so, with enough storage, no problem. He also makes sure he doesn't let his ac run at high cost times, worth looking into.

jp_2

say what????

so are you saying the work needed to move the air is free?

gotta subtract the work done, moving air, from the total load.