oil fired vs. electric

Brad White_73

Chris, this is the basis of what you seek.

Domestic hot water usage varies so widely. There is no average family. A single dad with five pre-teen sons will use less hot water than an elderly widow.
A single mom with five teenage girls will use more hot water than a Denny's restaurant with an attached car wash.

Let's assume your incoming water is 50 degrees and you heat it to 130 degrees (80 degree rise). Every gallon per minute (8.33 lbs. per minute) you take "from street to temperature" is 666.4 BTU's per minute. 39,984 call it 40,000 BTU's per hour if continuous flow, and that is net output.

If oil-fired, I would figure 75-80% efficiency or 49,980 to 53,300 BTUH input per GPM input rate. I would figure about 15% of your fuel usage to be standby losses, just a guess. Through-put of cold water is the obvious biggest loss.

If your shower is 106 degrees (mixing 50 degree cold at the valve for a 3 GPM total head flow) your typical shower net hot water rate will be 2.1 GPM (70% at 130F, 30% at 50F). Ten minute shower? 21 gallons times how many showers?

Laundry? Variable, immensely so. Dishwashing, take your pick. Point being, you should take an inventory of hot water usage. If I had to guess, for a family of five, maybe 50 gallons of HW per person per day? 21 for the shower and the rest shared? Just a guess. 250 GPD total?


If electric at 100% efficiency assumed, you would need 11.7 kW in that same hour. Most 40 gallon heaters have 9.0 kW in two (2) 4500 Watt elements which explains why the pick-up rate/recovery rate is so low. Commercial tanks can better this but the elements become huge. I have seen 50 gallon heaters with over 50 kW in them. Yikes.

Sorry to ramble, just wanted to get the numbers out there.

chris_75

Could someone give me a breakdown or send me in the direction to find this answer. What would be the breakdown of cost per operation between a 40 gallon oil fired water heater compared to a 40 gallon electric water heater for the year.Thanks

Edward A. (Ed) Carery

Op Costs

Chris,

There was a topic similar to this that was posted only a few days ago. In that case the home owner had an extremely low rate on electric, (about 1/2 of what I pay in NE Pennsylvania), and a fairly high rate on fuel oil.

That is unusual as Fuel Oil is normally much more cost effective in comparison.

First thing you need to do is compare your BTU prices in your area. The link below if a basic way to plug in your per unit costs and start.

If you decide that they are close, then you can ask additional questions regarding types of systems as you wish.


http://www.hearth.com/fuelcalc/findoil.html


Good Luck

Ed Carey

Edward A. (Ed) Carery

PS To pevious post

There is no comparison to the quantity of DHW that can be made by an electric 40 gal vs an oil 40 gal.

The oil DHW heater will make DHW about 4x as fast. (Much more DHW from oil than elect).

They are not even close to equal, and the oil will cost more to install as a result.


Ed

chris_75

I'm trying to come up with a rough estimate on the savings between switching a electric water heater to an oil fired. Based on the link above comparing the cost of each to produce the same btu output, how would I breakdown each? Does anyone know what the average household (say a family of 5) use for total btus in a given year?

Paul Pollets

Question??

Chris, If you're using an oil-fired boiler to heat the home, why not add an indirect DHW tank? It's far more practical and efficient.

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