Can you check my math on BTU for home heating?

[capslock118]

We are looking to move; the house we are looking at is natural gas heated. Our house is oil heat so I am curious to know the difference in cost.

What I decided to ask instead is, how much would it cost to heat my home with natural gas?

Natural gas in CT is measured in CCF (or therm). 1 CCF is $1.1008 after supply and delivery + $15 per month service charge.- this is the general-use rate and not the heat-only rate which is cheaper per ccf.

Heating oil is $3.949 per gallon today

Heating oil is 140,000 BTU per gallon
Natural Gas is 100,000 BTU per ccf (therm)

I use 830 gallons of oil per year on avg.

140,000 BTU * 830 gal = 116,200,000 BTU per year

116,200,000 BTU / 100,000 ccf (therm) = 1,162 CCF per year

(1,162 CCF * 1.1008) + ($15 flat rate + 12 per month) = $1,459
830 gallons * 3.949 per gallon = $3,277

The oil use is about right for us. So is natural gas really that cheap or did I do my math wrong? I was to the understanding oil and natural gas prices are about the same.

 

[aspeck]

Re: Can you check my math on BTU for home heating?

My understanding is that natural gas burns cleaner AND more efficiently. Your natural gas prices are similar to ours, but your oil prices are almost $0.50 per gallon higher than ours. Just looking at that, and knowing what I know from around my area, I would say your calculations are a decent ball park.

 

[capslock118]

Re: Can you check my math on BTU for home heating?

good to hear.

My understanding is that natural gas burns cleaner AND more efficiently

yeah i've heard that too - let's work that out...


oil BTU per gallon: 140,000
natural gas BTU per CCF: 100,000

oil heating efficiency: 70%
natural gas efficiency: 92%

140,000 BTU * .7 = 98,000 effective BTU
100,000 BTU * .92 = 92,000 effective BTU

guess it depends on what we're talking about; actually that made me think, i need to add that efficiency as part of my calc.

data source: http://www.ag.ndsu.edu/pubs/ageng/structu/ae1015.htm

 

[Tim Frank]

Re: Can you check my math on BTU for home heating?

good to hear.
yeah i've heard that too - let's work that out...


oil BTU per gallon: 140,000
natural gas BTU per CCF: 100,000

oil heating efficiency: 70%
natural gas efficiency: 92%

140,000 BTU * .7 = 98,000 effective BTU
100,000 BTU * .92 = 92,000 effective BTU

guess it depends on what we're talking about; actually that made me think, i need to add that efficiency as part of my calc.

data source: http://www.ag.ndsu.edu/pubs/ageng/structu/ae1015.htm

Are you sure about those efficiencies?
That will be a function of the specific furnace and the figures in that article are completely arbitrary....and old (2002).

 

[capslock118]

Re: Can you check my math on BTU for home heating?

well, i wasn't expecting an up-to-the-minuite accuracy. The 830 gallons of oil i use per year is an average. 2009 I used 900 some and 2010 I used 700 some and this year we are probably going around 800 or so.

so - just a rule-of-thumb, general idea is good enough for me.

plus, my oil furnace is at least 10 years old so I would guess that data source is close to accurate for my furnace.

 

[Bob_VT]

Re: Can you check my math on BTU for home heating?

Oh there are MANY more factors for BTU consumption/output.

Are you in an area where the outside temp is really low and you must heat the home. As an example if it is 40 outside and you need to have the home at 70 ......that is a 30 degree increase where here in VT it may be 30 outside and I need to raise/maintain the interior temp up 40 degrees to reach 70.

Your insulation and windows are HUGE factors in maintaining the temperature. I have all double insulated glass, I use an electronic set-back thermostat and I constantly update my insulation. My home is at 70 only during these hours M-F 6-8 AM and 6-10 PM then on Sat and Sun 7 AM-10 PM. The rest of the time the house is set at 55. My home is heated in 2500 sq ft and I have an additional 1200 that I do not heat (and that is not including the basement too).

The size of the nozzle has a big impact on the BTU/Hr output.

It can be very very complicated however, most States have efficiency experts to help work it all out for you. I know here in VT who I can call to get the exact number's.

What type of heat do you have? Baseboard? Radiators? Hot Air? etc.

 

[roscoe]

Re: Can you check my math on BTU for home heating?

Contact the seller of the house, have him show you the units bought, or the dollars spent, over the last year or two.

He can get this info from the gas company.

Or you can, if you get his gas company account number.

easy, free, accurate.

 

[hrdwrkingacguy]

Re: Can you check my math on BTU for home heating?

I guess I live in Arizona and I haven't worked in other parts of the country, but 92% furnaces here are hard to come by...Everything here is 80% efficient...Some really high end condensing furnaces are 90ish%...It all depends on actual unit efficiency to see what consumption will be...It also depends on home construction, insulation, windows, unit sizing...

There isn't much in the way of rules of thumb when it comes to sizing...load calculations are the right way to figure it out...Some people do with a 70,000 btu unit what it takes others a 120,000 btu unit...

 

[capslock118]

Re: Can you check my math on BTU for home heating?

Everything you ladies/gents have said are valid concerns for the house we are looking at; very true.

However, I was simply just trying to keep all other variables constant to get a rough idea and to be sure the math is right.

Again the question I asked myself was

how much would it cost to heat my home with natural gas?

I should have been more explicit and said, all other factors equal i.e. my homes insulation does not change, my windows do not change, I keep the house at the same temp. when switching to a different fuel source (FYI: we keep our house at 63 degrees at all times in the winter, we live in CT) etc, what would be the equivilant cost for natural gas versus oil.

So really, the only factors being changed are oil to gas, possibly oil furnace to gas furnace? (aside from the obvious pump and motor, not sure if the furnace itself would be replaced, I would doubt it).

we do have 'baseboard radiators' - i.e. radiators of hot water that are in the shape and size of baseboard - but in my question, we wouldn't change that variable.

 

[hrdwrkingacguy]

Re: Can you check my math on BTU for home heating?

Everything you ladies/gents have said are valid concerns for the house we are looking at; very true.

However, I was simply just trying to keep all other variables constant to get a rough idea and to be sure the math is right.

If that's the case then yes your math is correct...Would I write the checks out early? no...

You say you have an oil fired furnace, then you say you have baseboard radiant heat...Do you have a force air furnace(oil fired) and a hydronic boiler(oil fired) for baseboard heat? Or do are you going from a hydronic system in your current house to a force air system in the new house...

It's the same as saying I can drive from point A to point B on 100 gallons of gas in my car...Will a sherman tank get as far with 100 gallons of gas...

 

[bruceb58]

Re: Can you check my math on BTU for home heating?

You can get a 80% gas furnace all the way up to 96%. For my house in Tahoe, I chose the 80% because the extra cost of the 96% furnace wouldn't justify the savings in gas. I determined it would take nearly 10 years to get the savings back. Another thing to consider with the high efficiency furnaces is the cost of repair. A gas valve on a 80% furnace might be $100 where the high efficiency furnace would be $400. My heating guy felt the high efficiency furnaces are just too expensive right now because of the repair cost.

 

[capslock118]

Re: Can you check my math on BTU for home heating?

Or do are you going from a hydronic system in your current house to a force air system in the new house...

Keep the variables down, we are talking about one house only, my current house - and theoretical cost of using natural gas versus oil - in the same house. Obviously things will be different in another house; size, insulation, age of heating system. To answer your question though, all the homes we are looking at are 1920s or earlier, so nearly all will be radient.

You say you have an oil fired furnace, then you say you have baseboard radiant heat...Do you have a force air furnace(oil fired) and a hydronic boiler(oil fired) for baseboard heat?

I'm not sure of the exact terminology however:
my house uses oil to heat the hot water in our sinks - this is indirect as the water tank is seperate from the oil burner.
my house uses oil heat to heat the home - it is not forced air, it is radient baseboard.

i am using my term of "radiant baseboard" becase:
a) not 100% on what else it would be called
b) it's not like the old style radiators that are cast iron, they look like the electric baseboards you can buy at home depot
c) hot water circulates through them, making them radiators.

so they look like baseboards, they are radiators - hence my use of the term radient baseboard.

It's the same as saying I can drive from point A to point B on 100 gallons of gas in my car...Will a sherman tank get as far with 100 gallons of gas...

maybe, but the car would be like a 1200 sq ft home and the tank would be a 4000 sq ft home. I think a better analogy of what we are talking about is the difference of the same model cars but one has a V4 gas and the other a V6 diesel.

 

[j_martin]

Re: Can you check my math on BTU for home heating?

Simply put, natural gas is much cheaper than fuel oil
Also, a gas furnace can easily run much more efficiently than an oil furnace.

It's actually a little better than your original calculations (by the efficiency part)

Everything else in this whole thread is beside the point, but may be useful information.

hope it helps
John

 

[Tim Frank]

Re: Can you check my math on BTU for home heating?

OK, I guess we all missed the point.
If you are moving OUT of your house, why did you want to know what it will cost to heat it if it is switched to gas from oil?..doesn't seem likely that you are going to do that if you are moving...

Anyway, that is why I was confused, and I suspect why you got such a range of responses.

So your math is fine, but you would need to figure out the cost/amortisation of the new equipment.

 

[hrdwrkingacguy]

Re: Can you check my math on BTU for home heating?

Ok I do understand the question was only about a math problem...The math problem is correct...

For informational purposes only...Heating water and heating air are two different things entirely...If you have baseboard heaters they are using water heated from a boiler...Then the heat radiates through the room...Forced air heating is air flowing around a heat exchanger and a supply fan blows it through the duct work through the house...Water is way more efficient at transfering heat...

Operational cost from a hydronic system vs. a forced air system will never be the same, in the same house...

 

[j_martin]

Re: Can you check my math on BTU for home heating?

Ok I do understand the question was only about a math problem...The math problem is correct...

For informational purposes only...Heating water and heating air are two different things entirely...If you have baseboard heaters they are using water heated from a boiler...Then the heat radiates through the room...Forced air heating is air flowing around a heat exchanger and a supply fan blows it through the duct work through the house...Water is way more efficient at transfering heat...

Operational cost from a hydronic system vs. a forced air system will never be the same, in the same house...

BTU's is BTU's. Medium makes no difference except for the losses. Back in the days of leaky uninsulated air ducts and the furnace in a cold basement or crawl space, this might be true. In a modern installation with losses controlled, and the space near the furnace (basement) heated anyway, it really doesn't make any difference what medium you use to transfer the heat.

Hydronic is easier to zone control, which generally reduces demand because you don't heat what you're not using. However, air can be zone controlled also.

my 02
John

 

[hrdwrkingacguy]

Re: Can you check my math on BTU for home heating?

BTU's is BTU's. Medium makes no difference except for the losses.

my 02
John

So why does a water cooled chiller cost 40% less to operate then a air cooled???

 

[Tim Frank]

Re: Can you check my math on BTU for home heating?

So why does a water cooled chiller cost 40% less to operate then a air cooled???

You are supposed to be the A/C guy, I was kind of expecting you'd know......if you don't, PM me and I'll explain it.

This thread was intended to be about the cost of a BTU of heat generated from oil vs gas....just about everyone (including me) has managed to make it about something else). Thankfully nobody mentioned ground-source heat pumps....

John's summary was dead on and actually relates to OP's question.

 

[CharlieB]

Re: Can you check my math on BTU for home heating?

If the OP is simply changing the BURNER in his furnace to switch from oil to NG then his calcs are fine.

If he is considering changing the whole FURNACE to take advantage of possible increased efficiency of a new furnace then his calc would need the efficiency factor added.

K.I.S.S. principle.

'Nuff said.