# Comparison of DHW Oil Indirect vs Electric Tank



## velvetfoot (Sep 5, 2012)

Now, I've been thinking about this for the last couple of days and I might have had a breakthrough is proving to myself that an electric heater is cheaper to run, at least when that's the only thing that's being run (either summer, or maybe winter too if the stove is running and heating the house for the most part).

The DOE test procedure requires, in part, heating 63.4 gallons of water to 135F, and the test takes place over 24 hours.  
I'm pretty sure, again, based on memory and some readings I took off my water softener, that my entire inside useage is 40 gallons per day.  I figured 30 gallons of that was hot water.  I was able to use that number to use the annual kwh on the Energy Guide yellow tag, which, typically seems to be 4773 for a 40 gallon tank.  Electric cost was assumed $.15/kWh.

The oil consumption I got from looking at some past bills, but because of the periods and a different owner, maybe not that confident..could be lower.  AVC8130's might be better, or it could be something in the middle - I put all three in the attached spreadsheet.

I couldn't believe it when those three annual oil use scenarios came out to $1037, $526, and $701, respectively, and the electric scenario came out to $334!  It blew my mind.  This is with 15 cent electric.  Resistance, not heat pump.  And, a $240 water heater.

Please tell me if I'm wrong!  

I'll get working on firming up my oil and water consumption numbers, but I think they're in the ballpark.

(Also, Moderators, not sure if this is the right forum to post this, but there have been other similar threads here of late. )


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## velvetfoot (Sep 5, 2012)

I haven't put the oil on a timer yet.  If my water consumption is right, I'd have to get down to .24 gallons/day of oil to break even with oil.  Seems low, but maybe it's possible.  Need an hourmeter.

If it works out, or it's close, it would be nice to get off the oil.


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## WES999 (Sep 5, 2012)

I just checked the hr meter on my electric water heater. In 69 days, 17 hr on time.
That comes out to just over $5/mo.

I was using about $100/ mo with oil.


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## velvetfoot (Sep 5, 2012)

But, as I recall, you have a solar booster of some sort, and it is summer, but, an 80 gallon tank. 
Too bad, for me  , you have solar, or it'd be more of an apples to apples things.

The actual number for oil used is also close to mine.  Not sure what setup you have/had.


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## tom in maine (Sep 5, 2012)

Dick Hill runs timers on everything and collects the data every Sunday night.
He found that his low mass, cold start oil boiler with a separate Amtrol tank for DHW was operating at 33% efficiency during the summer.
This is in a house with tenants, so the usage was higher, which would, in theory be better for efficiency.

I would expect a tankless coil boiler to be way under that in the summer.


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## rkshed (Sep 5, 2012)

Funny this is coming up now.
I have been considering trying a timer in my electric hot water heater as the only times hot water is needed is morning and night. I know its heating during the day just to keep the temp up but would it cost more only heating 2 times daily as opposed to all day? Would a modern tank lose enough heat while off to make a timer ineffective?


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## velvetfoot (Sep 5, 2012)

Wow, 33%!  That's lower than I thought.  I have a similar setup with BoilerMate and cold start Burnham v8 boiler (not sure if that's considered low mass, because it seems to hold 20 gallons or so.


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## Redbarn (Sep 5, 2012)

We switched our DHW from using oil (1 gall per day, $110 / month) to a Geyser HPWH ($15 a month average).

We also use the HPWH as dehumidifier/ air conditioning in the summer and use a timer to run the HPWH at times convenient to us. In the winter, our basement stays above 55 deg F and so we can use the HPWH all year round. Run times do extend in the winter but I estimate we are still saving.
Kept the oil system intact (as its paid for !) as backup for use when we get a full house but otherwise it sits idle.

Cannot figure how oil DWH can compare to electric DHW in the summer..


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## velvetfoot (Sep 5, 2012)

Did you put the new hw heater in series downstream from the indirect.

Our basement gets into the 40's as I recall, and I insulated the walls (but not the floor).  With the insert, my aim is not to run the boiler at all, but my wife has something to say about that, so it does get run.  It still can get pretty cold in the basement.

I don't know how much the oil usage could go down with a timer, but 33% is quite the shocker.  I was thinking 40% w/o timer, based on another thread.


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## WES999 (Sep 5, 2012)

> But, as I recall, you have a solar booster of some sort, and it is summer, but, an 80 gallon tank.
> Too bad, for me  , you have solar, or it'd be more of an apples to apples things.
> 
> The actual number for oil used is also close to mine. Not sure what setup you have/ha


 
Yes I have 1( soon to be 2) 4'x 8' solar collectors on the roof preheating the water. But even without the solar I estimated $20-$25/ per mo for the electric water heater. Still cheaper than oil.




> I have been considering trying a timer in my electric hot water heater as the only times hot water is needed is morning and night. I know its heating during the day just to keep the temp up but would it cost more only heating 2 times daily as opposed to all day? Would a modern tank lose enough heat while off to make a timer ineffective?


 
I don't think a timer would save much unless you can take advantage of off peak rates.
http://www.leaningpinesoftware.com/hot_water_heater_vacation.shtml
This site makes a good case that you would not save much.

The standby loss in a quality water heater is not much. Better to just add extra insulation IMO.


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## avc8130 (Sep 5, 2012)

velvetfoot said:


> Wow, 33%! That's lower than I thought. I have a similar setup with BoilerMate and cold start Burnham v8 boiler (not sure if that's considered low mass, because it seems to hold 20 gallons or so.


 
Trust me, I pooped a brick when I thought of the concept of 1 gallon/day.  Then I had a sigh of relief when I found out it was closer to 3/8.  Then I did the math again and pooped.  

Oil is NOT worth it for heating water any more.

ac


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## BoilerMan (Sep 5, 2012)

tom in maine said:


> Dick Hill runs timers on everything and collects the data every Sunday night.
> He found that his low mass, cold start oil boiler with a separate Amtrol tank for DHW was operating at 33% efficiency during the summer.
> This is in a house with tenants, so the usage was higher, which would, in theory be better for efficiency.
> 
> I would expect a tankless coil boiler to be way under that in the summer.


 
I'm glad someone said it! 

Remember that some oil boilers in humid basements don't do well for a cold summer, some don't bother at all.  If your going to be gone for a weekend, try turning the whole thing off and running the hot water out.  Be shore to close the mackup water valve.  I've seen boilers leak between sections when allowed to cool down.  If all seems well, put in an electric, valve off, and drain the indirect.  I've put in many electric WH so people don't hear that oil burner running in the summer.  With no flue to draft heat out, most EWH have a 94% efficiency only 6% jacket loss which can be reduced more with a fiberglass blanket.  I like to put a brass swing check on the hot outlet installed right off the tank's nipple to block any convection through the hot line.  Those little rubber heat traps that come on the tank don't last more than a year IMO. 

TS


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## velvetfoot (Sep 5, 2012)

I know, just for hot water.  I can drive the 44 miles roundtrip to work in my Mini for a gallon.  Wouldn't make any impression at work without washing up though.


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## velvetfoot (Sep 5, 2012)

Why wouldn't you keep the indirect hooked up to act sort of like a buffer tank?  Of course it would be insulated, and not pick up ambient heat that well.


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## nrcrash (Sep 5, 2012)

I am in the process of installing a Geospring water heater which uses about 1/3 the electricity to use in the summer if I do not feel like firing up my wood boiler w/ storage.  Best part is that Ngrid is giving me a rebate for the cost of the unit itself.


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## BoilerMan (Sep 5, 2012)

Heat pump water heaters are great, especially if you already de-humidify.  I'm just not sold on the longevity of them as of now......  you could duct that cooler air into the living space and pull warmer air from outside if the basement is cool and dry.  Two fold A/C and cheap hot water. 

TS


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## velvetfoot (Sep 5, 2012)

The equation changes with a wood boiler in the mix.


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## kopeck (Sep 5, 2012)

Wow, makes me really wonder about the indirect I have in my basement.  I have a 40 gallon electric hot water heater sitting in my barn that was working when I pulled it out a few year ago.  The thing I don't know about is the best way to hook the two up so I could easily switch back and forth.

33%, man that's bad.

K


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## BoilerMan (Sep 5, 2012)

Yeah, the 1/3 number is common but people just don't want to believe it, although there are still some tankless coil guys out there that i'm gonna guess are at 1/4 or less.  Even with a cold start boiler, you have to heat up the CI, the boiler water to say 140 and now circulate that 140 water through a coil in cooler DHW.  Tank up to temp, turn it all off and let the CI boiler, and it's 20 or so gallons of water cool and draft all that heat up the chimney.  It's just bad all the way around, burning oil in the summer in a house that you want to be cool, seems kinda sideways.  Although I do it, just not with my indirect, instantanious on a switch near the shower.  Turn on, wait 20 seconds and you have endless hot water.  Cheap guy like me: turn off during shower (low voltage) and shower till water rund cold, less than three minutes.  Easy, and I have my wife trained and she puts up with me still......

TS


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## rkusek (Sep 6, 2012)

WES999 said:


> Yes I have 1( soon to be 2) 4'x 8' solar collectors on the roof preheating the water. But even without the solar I estimated $20-$25/ per mo for the electric water heater. Still cheaper than oil.
> 
> 
> 
> ...


 
How much $ do you have in your solar setup?  Is it a drainback?  Does it still help in winter?  I'm reading this thread thinking my 80 gal electric is probably not too bad but I know we use a lot of hot water.  I want to build a sidearm that uses the 6-7 small tubes inside the bigger shell for the winter months when the wood boiler runs.  I was hoping I could use the same homemade sidearm with a solar setup during the summer.


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## jebatty (Sep 6, 2012)

> ... and the electric scenario came out to $334! It blew my mind. This is with 15 cent electric. Resistance, not heat pump. And, a $240 water heater. Please tell me if I'm wrong!


 
The thought of resistance electric sometimes is perceptually not cool. To repeat some prior posts of mine, our resistance electric bill is about $4.00/mo, or $50/yr. Wife and I, occasional guests mostly during the summer. We don't consciously minimize our hot water usage, although we by habit don't waste much of anything. That electric bill was about $8 month until we super-insulated our hot water heater, added insulation to hot water pipes, and added U-shaped heat traps on the hot water heater. Cost of all of that "extra" was about $50.


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## maple1 (Sep 6, 2012)

avc8130 said:


> Oil is NOT worth it for heating water any more.
> 
> ac


 
I haven't seriously crunched my numbers, but have come to the same conclusion: get the heck off the oil.

Even with a cold start boiler & indirect tank, electric is cheaper.

For 15 years I had a coil in a combo boiler that stayed warm all year, and estimate that I was using about 150 gallons of oil per year solely for DHW in the off-heating season. That was keeping the boiler set as low as possible, and not using that much DHW (showers are cooler in the summer), and lighting the odd wood/waste paper fire to heat the boiler now & then. I turned that boiler off around the first of August, after getting my new 80 gallon electric tank in, hooked up, and on line. Only had one power bill since then, to August 23. I think it was only up around $10 from previous months. The next bill should give a better picture. Seems pretty obvious if you think about no chimney for heat to go up, no pipes in between for heat to radiate off of, all electricity used is going right into heating the water, way better insulation - likely more factors too.

Then add in the thoughts of getting rid of the oil tank & associated liabilities & space gained in doing so....


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## velvetfoot (Sep 6, 2012)

You'd still have to have some sort of backup heat.

An update:  I found some old notes and found that I use about 44 gallons/day of softened (inside house) water.  Might affect numbers some, but I still don't know how much of that would be hot water (I assumed 30).


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## peakbagger (Sep 6, 2012)

With a "hot" oil boiler with the aquastat turned down, my oil consumption dropped about 1 gallon per day for about 5 summer months. When I installed my solar hot water system and shut down the boiler for the same five months, I obviously didnt use any oil. I expect the standby loss of the boiler was far more than the hot water usage as I dotn use  much hot water. 

These days instead of installing solar hot water, I would install a Heat pump hot water heater and a couple of extra panels of solar electric panels. When I put in the SHW, solar electric panels were 6.50 per watt, my last batch I bought were 93 cents a watt.


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## maple1 (Sep 6, 2012)

velvetfoot said:


> You'd still have to have some sort of backup heat.


 
Two year old electric boiler c/w circulator, found for $400 on Kijiji. My oil days are almost completely over. (I'll wait until I get this winter in before pulling the oil tank out - but the fill pipes will be disabled this coming weekend).

YMMV, of course.


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## velvetfoot (Sep 6, 2012)

Did you replace the CC500, then?


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## maple1 (Sep 6, 2012)

In the process of replacing. I'll be doing a report on here when I'm done - pics & everything.


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## velvetfoot (Sep 6, 2012)

Fantastic.  I forgot which unit you chose, or are you keeping it a suprise?

I found some more oil bill usage, and it could be worse than I thought for the summer months where the info was there.
(I got the house and put an insert in in 2006.)
Should get an hourmeter for sure...


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## maple1 (Sep 6, 2012)

One more off-topic reply.

Have had a Varm 40 sitting in my barn here since June. It's been a long distracting summer but time to really get down to nuts & bolts - er, pipes & fittings & stuff. It's starting to get cooler at nights - good thing I started this way back in May.


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## velvetfoot (Sep 6, 2012)

Awesome!


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## velvetfoot (Sep 26, 2012)

Over the past eight days I've used an average of 13.2 kwh/day, which projects out to 396 kwh a 30 day month, which is 131 kwh more than last September's number.  This comes out to 1572 kwh /year for the water heater, which is considerably lower than the 4773 kwh on the yellow label.  At my electric rates, that comes out to $236/year which is a savings of $800/year over oil, which I calculated at .74 gallons/day.  These numbers would seem to justify the move.  Hopefully they're in the ballpark.

Did I mention that it is totally quiet?


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## DBoon (Sep 26, 2012)

Hi Velvetfoot - the savings you are getting with the electric hot water heater are real.  I tried to find a previous post where I worked out the math, but I think my assumptions were electricity at $0.11/kWh (overnight rate), electric hot water heater at 100% efficient (assume standby losses the same for both electric and oil) and oil heated hot water at 65% efficient. I found that ~$2.75/gal of oil was the point above which electric was cheaper.  I re-calculated below.  

Calculations:
Oil at (140,000 BTUs/gallon / $COSTOIL/gallon) x 0.65 efficiency = 91,000 BTUs/$COSTOIL
Electric at (3414 BTUs/kWh / $0.11/kWh) x 1.00 efficiency = 31,036 BTUs/$

(91,000 BTUs/$COSTOIL)/(31,036 BTUs/$) = $2.93 per gallon of oil as the break even point.  Many have already stated that the efficiency should be in the 30 to 50% range, and if you figured that, the break even $/gal of oil would be $1.35 to $2.25/gal (assuming $0.11/kWh for electricity).  If you assumed 90% efficiency (maybe possible with the most efficient and newest of systems, but not likely) for oil, then the breakeven point would be $4.05/gal - which goes to show that it is hard to imagine why anyone would heat DHW with oil unless their electric rates were sky high, and if they were, I would just encourage them to get a HPWH to halve the effective cost with electric.  This doesn't count the cheaper installation and maintenance costs for electric, of course.


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## TheMightyMoe (Sep 26, 2012)

http://nepacrossroads.com/fuel-comparison-calculator.php

BTU calculator.

.25 Cents per KW vs 4 per gallon oil for me.

I'm on oil =/ Even with stand by losses oil is cheaper for me, and since the majority of the year is heating/shoulder, the standby heat just goes into the house, no real loss there.


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## velvetfoot (Sep 27, 2012)

The basement gets pretty cool over the years with burning the wood insert upstairs, so I think I'm going to stick with the electric water heater over the winter too.  It'd be nice if propane got cheaper around here.  I have to check the price.

Still higher than oil here, with higher efficiency for propane boiler, nevermind less maintenance.  Still tempting to switch if the oil boiler craps out: cleaner, instant hot water/heat possibile (no/less standby loss), tank outside for more room inside, standby generator).

oil:  3.92/gal
propane:  2.96/gal
electric (net):  .15/kwh


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## maple1 (Sep 27, 2012)

Quite a bit of the standby heat when heating with oil goes right up the chimney. A cold start boiler can help with that, but there will still be some heat loss to the outdoors. I'll add to this thread on tankless coil oil vs. electric once I get another power bill or two, but for now after the first one I'm estimating I'm saving close to $100/month in the summer non-heating season with the new electric tank.


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## velvetfoot (Sep 27, 2012)

I have a cold start indirect and I still figured I'm using .74 gal/day.  Of course, any of my numbers could be off.  
I've been taking daily readings off the electric meter.


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## JP11 (Sep 27, 2012)

velvetfoot said:


> I have a cold start indirect and I still figured I'm using .74 gal/day. Of course, any of my numbers could be off.
> I've been taking daily readings off the electric meter.


 
Your numbers are similar to what I had.  I probably averaged closer to 1gal.  I have an 80gal indirect.. and run a recirc line on a timer quite often.  I'd rather fire the boiler once ever two and a half to three days.  Armload of splits is much cheaper than 2 to 3 gallons of oil.. even if I'm running 70% homemade bio fuel.

JP


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## velvetfoot (Sep 27, 2012)

35508 was a good thread:  https://www.hearth.com/talk/threads/cost-to-heat-dhw-with-oil-tankless-update-1-month-later.35508/

It'd sure be nice to have a gasifier with storage.


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## steam man (Sep 27, 2012)

I think I did this sometime ago but here are my calculations. Correct me if any assumptions/math is wrong. I am not seing the big savings with an electric water heater at oil's current price. Here goes:

Assume 4773 KWH yearly use for hot water as per the DOE spec. At 16.4 cents/kwh, (my rate) that is $782.00/year. For oil, 4773 kwh = 16286153 btu's. Assume #2 oil is 138,500 but/gallon. At 80% efficient (mine is higher), I get 110,800 useable btu's/gallon. 16286153 btu's/110,800 btu's gallon = 146.98 gallons oil/year. At (my rate) $3.64 gallon, that is $535.00/year, $247.00 (68 cents/day) less than electric. To be equal, oil would have to be $5.32/gallon. Another angle would be that if your oil appliance was only 55% efficient, the hot water bills would be the same.

We assumed both heaters have the same standby losses but the boiler has some. I figure a 20 gallon boiler going from 180 deg to 100 deg once a day would lose about 12,480 btu and cost maybe 40 cents/day. Many boilers have burner dampers that close to prevent stack loss as does mine. Incidentily, I have a power venter so no chimney losses. You also have operating cost for an oil boiler which, ironically, electricity is needed. I am not sure what the consumption is but I will look into it. Maintenance/installation cost are a consideration. The only way you can compare is life cycle cost between them.

It would seem at this hot water useage example, it is a wash between the cost of oil or electric in this situation. I do have a 100 tube evac solar array for domestic water so I can't really use a real world example.


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## JP11 (Sep 27, 2012)

velvetfoot said:


> 35508 was a good thread: https://www.hearth.com/talk/threads/cost-to-heat-dhw-with-oil-tankless-update-1-month-later.35508/
> 
> It'd sure be nice to have a gasifier with storage.


 
Wow..  the math is so much better now.  If I had read that thread when I built my house.. I would have for sure put in an electric for summer months.  It just makes sense.  Sure, an indirect is great when the boiler is running anyway... but in summer...  It's a huge waste.

Now.. I just need to get the wife onboard with a simple fire once every 2.5 days in summer, when I'm away that is.

JP


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## nrcrash (Sep 27, 2012)

Just got my Geospring up and running.  Now I can take my time with the vigas install and not have to worry about getting my DHW from oil!


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## maple1 (Sep 27, 2012)

steam man said:


> I think I did this sometime ago but here are my calculations. Correct me if any assumptions/math is wrong. I am not seing the big savings with an electric water heater at oil's current price. Here goes:
> 
> Assume 4773 KWH yearly use for hot water as per the DOE spec. At 16.4 cents/kwh, (my rate) that is $782.00/year. For oil, 4773 kwh = 16286153 btu's. Assume #2 oil is 138,500 but/gallon. At 80% efficient (mine is higher), I get 110,800 useable btu's/gallon. 16286153 btu's/110,800 btu's gallon = 146.98 gallons oil/year. At (my rate) $3.64 gallon, that is $535.00/year, $247.00 (68 cents/day) less than electric. To be equal, oil would have to be $5.32/gallon. Another angle would be that if your oil appliance was only 55% efficient, the hot water bills would be the same.
> 
> ...


 
How do you heat your DHW now and what is your actual annual cost? Depending on the setup, I think oil DHW heating would be lucky to be 50% efficient in some cases.

I'm early in my evaulation, but I know that over the last 6 years or so, I was using on average about 150 gallons (Canadian) of oil for heating DHW in the off-heating season (about 6 months). My last electric bill, for which I had my electric tank up & running for close to half of the billing period (one month out of two), was about $20 more. I had a tankless coil oil boiler that had to stay hot (140-150) all the time. I admit my math is pretty fuzzy so far - I'm expecting the next electric bill will show more of an increase. But I also have yet to add insulation to the electric water tank, which is also in my plans.


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## velvetfoot (Sep 27, 2012)

nrcrash said:


> Just got my Geospring up and running.  Now I can take my time with the vigas install and not have to worry about getting my DHW from oil!


That's shorter than I thought it'd be.


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## nrcrash (Sep 27, 2012)

Only 50 gallons.  But it was also FREE from Ngrid!


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## steam man (Sep 27, 2012)

maple1 said:


> How do you heat your DHW now and what is your actual annual cost? Depending on the setup, I think oil DHW heating would be lucky to be 50% efficient in some cases.
> 
> I'm early in my evaulation, but I know that over the last 6 years or so, I was using on average about 150 gallons (Canadian) of oil for heating DHW in the off-heating season (about 6 months). My last electric bill, for which I had my electric tank up & running for close to half of the billing period (one month out of two), was about $20 more. I had a tankless coil oil boiler that had to stay hot (140-150) all the time. I admit my math is pretty fuzzy so far - I'm expecting the next electric bill will show more of an increase. But I also have yet to add insulation to the electric water tank, which is also in my plans.


 
The funny thing is I couldn't figure my hot water consumption expense with any accuracy. I heat DHW with a 100 tube solar array year round. I also use wood to heat DHW at times along with oil. I also have a cold start boiler with 8 gallons of water in it and no chimey so there is no heat loss per say there.

The irony of using electric to heat hot water is that it is really only about 30% efficient by the time the power company creates it and gets it to you. What they use for fuel is a big factor along with the delivery charge. With many plants changing over to natural gas (being even cheaper than coal now), electric rates have stayed flatter over time than other fuels. Certainly there is a point on the cost graph where electric is cheaper than oil.


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## maple1 (Sep 27, 2012)

There are likely big effiency losses in oil too from the time it is found in the ground in its raw form until the time it gets in your oil tank ready to burn. I think the only 'real' way we have to try to estimate the differences is to compare actual real world monthly fuel expenditures in a before & after scenario. I don't recall reading from anyone who switched from oil to electric or vice versa that oil is cheaper - but maybe I missed it and it is in certain situations.


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## TheMightyMoe (Sep 27, 2012)

Well I can guarantee you my electric bill went DOWN about 300-400 KWH per month, and that was around 80-100$ in monthly "savings". I can take a picture of that.

On my boiler I have a Aquasmart aquastat with a built in history.

IN THE SUMMER

My average stand-by burn time is 2 minutes with a 87 minute stand-by. (140 Low-limit with 20 diff)
Showers run it for 10-15 minutes with a 100-140 stand-by afterwards (Water is at 180 instead of low limit)

So with my .6GPH nozzle I figure around .68 hours or $2.76 a day or 95,200 BTU

Now if you do the math comparison...


Electric BTU = 350 KWH x 3070BTU (3412 BEFORE 90% efficiency loss) = 1,074,500 monthly BTUs total =
So...

Oil .68 gallons or .68x110952x30 days (138,690 BEFORE 85% efficiency loss) = 75447.36 = monthly 2,263,420 BTUs total
So...

OIL- Total BTU 2,263,420 / 110952 = 20.4 x $4 = $81.6
ELECTRIC - Total BTU 1,074,500 / 3070 = 350 x $.25= $87.5

On a BTU basis oil is cheaper, however, I do use many more BTUs due stand-by losses and inefficiency.

So the math adds up, and if I can get rid of stand-by times (8 months of the year during swing season / winter it rarely has to stand-by), oil is considerably cheaper. (19 minutes a day, or 9.5 hours or 5.7 gallons or $22.5 monthly savings)

HOWEVER,

For MOST people electric will be CHEAPER due to stand-by losses. If you can negate your stand-by losses, and have a very insulated Indirect DHW, oil maybe cheaper, especially if you have extremely high usage or are using a re-circulator hot-water pump in your home. (Cycling a 3500+ Watt heater vs firing a oil boiler...) The other benefit of a indirect water heater, is they come with a aqua stat with a adjustable differential, in the winter my differential is 20*, but in the summer it is 5*. This is because in the winter, the boiler is usually hot, in the summer it is just maintaining. In the winter I can take a shower without the DHW even coming on.

The math adds up comparative to my usage.


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## maple1 (Sep 27, 2012)

OK - with $0.25/kwh electric and $4/gallon oil, I could see where oil might be cheaper especially with heavy usage.

Here oil is somewhere around $1.20/litre (haven't bought any since Spring though), and electric is 0.15/kwh. I think 0.25/kwh is the highest rate I've seen posted on here.

Also, similarly to reducing standby loses on oil, they could also be reduced on electric with extra insulation. I'll be checking that out too after a couple more months, hopefully. I guess the same as with everything, YYMV.


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## TheMightyMoe (Sep 27, 2012)

Our power plant is run off oil... So we pay for oil... Then the power lost through transmission etc... Sucks =/

Insulation is not what I was referring to.

The stand by losses I am referring to are from the boiler/flue not the water tank.

In the winter, I have little / to no oil boiler stand by losses, because I am heating the home with it.

BTU for BTU oil is generally cheaper then electric, but since you have to maintain and heat a boiler, you have excessive stand by losses, especially in the summer, where stand-by heat is NOT WANTED.

Make sense?

Even at your energy rates, oil is cheaper then electric BTU for BTU.

$4.54 a gallon and $.15 KWH

Oil @ 38.51 million btu (85% eff)​Electric @ 48.85 per million btu (90%)​ 
The problem is turning oil into hot water VS electric to hot water is less efficient then using electric directly due to boiler stand by losses.​​But in large quantities / no stand by losses / certain situations oil wins out.​


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## velvetfoot (Sep 27, 2012)

I'll compare electric usage on my bills as time goes by;  nothing else too much is changing.


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## avc8130 (Sep 27, 2012)

I know beyond a shadow of a doubt that my oil burner ran .4 hours/day to make DHW this summer.  My nozzle is 1.25 gph.  That means I burned 1/2 gallon of oil daily for DHW ONLY with an indirect setup.  I paid $3.34 for the oil back in the spring.  That means it cost me $1.67/day for DHW this summer.  Over a 30-day month, $50.  

ac


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## TheMightyMoe (Sep 27, 2012)

avc8130 said:


> I know beyond a shadow of a doubt that my oil burner ran .4 hours/day to make DHW this summer. My nozzle is 1.25 gph. That means I burned 1/2 gallon of oil daily for DHW ONLY with an indirect setup. I paid $3.34 for the oil back in the spring. That means it cost me $1.67/day for DHW this summer. Over a 30-day month, $50.
> 
> ac


 
But the question is:

How much of this is direct heating? VS Maintaining the boiler?

Do you use a low limit on the boiler? Is it a cold start?

Etc...


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## R Mannino (Sep 27, 2012)

avc8130 said:


> I know beyond a shadow of a doubt that my oil burner ran .4 hours/day to make DHW this summer. My nozzle is 1.25 gph. That means I burned 1/2 gallon of oil daily for DHW ONLY with an indirect setup. I paid $3.34 for the oil back in the spring. That means it cost me $1.67/day for DHW this summer. Over a 30-day month, $50.
> 
> ac


1.25 GPH........do you live in a mansion?  My 2000 sq ft ranch has a 0.4 GPH nozzle (I have an indirect water heater too).  It's supposed to be a 0.5 GPH.  I'll wager with the correct boiler size and firing rate your DHW and heating use of oil would be drastically reduced.


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## TheMightyMoe (Sep 27, 2012)

R Mannino said:


> 1.25 GPH........do you live in a mansion? My 2000 sq ft ranch has a 0.4 GPH nozzle (I have an indirect water heater too). It's supposed to be a 0.5 GPH. I'll wager with the correct boiler size and firing rate your DHW and heating use of oil would be drastically reduced.


 
With a 1.25 GPH nozzle, depending on flow rates, the DHW will still run the boiler at max without short cycling in most cases. Most indirect WANT a 1+ GPH nozzle though, per specs.

Mannino with your .4 GPH nozzle, do you take short showers or run out of hot water? With a nozzle that small you are underfiring the DHW. (I am underfiring mine as well @ .6, and only run out of water if we are all taking consecutive showers)


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## R Mannino (Sep 27, 2012)

I haven't run my 42 gallon indirect out of hot water yet. I also don't have a Jacuzzi to fill either..................
I have the DHW on priority, I'm sure that helps   FYI, cold start.


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## TheMightyMoe (Sep 27, 2012)

Yeah, we have 4 people that shower in the morning in a row. =/ Mine is a 50, on priority, not cold start however, I want to but I don't want new controls. I've thought of up-sizing, but .6 is perfectly rated for the house.


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## avc8130 (Sep 27, 2012)

TheMightyMoe said:


> But the question is:
> 
> How much of this is direct heating? VS Maintaining the boiler?
> 
> ...


 

It is NOT a cold start, low limit is set at 130.

I have exact data for start and stop times of the boiler motor.  Generally the wife and I shower in the morning and then the indirect is just maintained at 120F.

Here is Aug 30 for an example:
8/30/2012 6:59:11 AM Turned ON 
8/30/2012 7:06:00 AM Turned OFF
8/30/2012 7:57:04 AM Turned ON 
8/30/2012 8:00:52 AM Turned OFF
8/30/2012 3:21:27 PM Turned ON 
8/30/2012 3:27:56 PM Turned OFF
8/30/2012 10:58:03 PM Turned ON 
8/30/2012 11:04:08 PM Turned OFF

For whatever it is worth, I shower at 6:50AM and the wife showers about 7:45AM.  

As you can see, it runs 7 mins when I shower and only 4 when she does.  This is most likely because the oil burner is just about at low limit when I shower and it is probably close to temp when she does.  Then it is 7 hours until the next 6 min firings.

ac


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## TheMightyMoe (Sep 27, 2012)

With your nozzle, you are gonna have very good recovery, and if the boiler is low mass you could probably cold start it and save another 20-40 a month.


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## velvetfoot (Sep 27, 2012)

Thing is, if anybody uses the hot water during the day, the whole boiler has to come back up to temperature, more like 190 on priority vs. the resultant 120 hot water.  Then it just sits there and cools off til the next time.


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## R Mannino (Sep 27, 2012)

velvetfoot said:


> Thing is, if anybody uses the hot water during the day, the whole boiler has to come back up to temperature, more like 190 on priority vs. the resultant 120 hot water. Then it just sits there and cools off til the next time.


 
Once we accept that the boiler will always be above the temperature of what it is heating, it shouldn't bother us as much.  The key it to eliminate the standby losses as much as possible.  Whenever your heating water for storage standby losses are inevitable.  The key to heating with oil is to have the lowest mass as possible, wood boilers different story.  Control is the other big issue, wrong control strategy can cost a lot of BTU$.


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## avc8130 (Sep 27, 2012)

TheMightyMoe said:


> With your nozzle, you are gonna have very good recovery, and if the boiler is low mass you could probably cold start it and save another 20-40 a month.


 
But won't that cause the boiler to condense?

ac


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## velvetfoot (Sep 27, 2012)

It bothers me that I have to heat up more mass and probably the same amount of water as the indirect tank and just let it cool its sorry self off between firings.  I don't know, but I wouldn't call that standby loss, and it does bother me.  Lowest mass as possible would be a tankless.  I have a Burnham V8 operated as a cold start, with a now-inactivated and drained Amtrol BoilerMate.  I'm using an outdoor reset for some setback (since it's not a mod con and I guess more importantly, the emitters are common baseboards, can't go too low I guess), but for dhw, I think it's gotta be at 190 on priority.


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## TheMightyMoe (Sep 27, 2012)

Your boiler manual will tell if you IF it can be a cold start. A low mass boiler should heat up so fast, that it will not condense long enough to be an issue or in the manual it may call for a system bypass or plumbing primary/secondary etc...

If you want to lessen the calls on the DWH, you can increase the size of the differential on the Indirect Water Heater aquastat, so hand washing etc, will not cause the boiler to run.

It is more efficient to heat water up from 80 to 180 while providing energy to your water heater then to reheat water from 100 to 140 for no reason.

Either way you will have stand by losses, and you have to figure out what is better for your house hold. Most people use a low limit because it is just more fool proof.

Velvet in your case, electric sounds like the way to go =) With baseboards 160 hi-limit is about as low as it should go for COMFORT, you can go lower, but usually that effects the comfort level of the home more then anything. 180-190 is typical priority hi-limit, and the control should by pass the setback hi-limit.


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## BoilerMan (Sep 27, 2012)

AVC, is there a way to tell how much 120F water you in those two showers?  What we need to do this totally right is a totalizer on the DHW pipe of the water heater/indirect.  avc has the oil numbers now if we can get the total gallons of actual hot water used.  Anyone have an old water meter kicking around?????  It would be as simple at calculating the needed BTUs for the termp rise of the water actually consumed divided by the oil used (timer on burner calculation.  *All the rest is standby loss.*  Boiler drafting heat up the chimney, jacket loss of boiler, jacket loss of indirect, loss from associated piping etc. etc. etc. 

AVC, I'd do a heat loss calc on your house, I've followed your threads on backup, type of house you have, and the rest.  1.25gph is alot of heat, you do not need it for DHW as you have proven. 

An underfired indirect is almost a given, as they spec them at riduclous flows and BTU inputs.  Here in the real world, we use hot water at a given rate, and if the boiler and stored hot water in the indirect can keep up, it is a non issue.  Look at heat pump water heaters, they make something like 2,500 BTU/hr but have large tanks to make up the difference, and electric elements for supplement.  Take a typical electric water heater at 4,500 watts, that = .135 gallons of oil at 80% eff. 

TS


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## avc8130 (Sep 27, 2012)

Taylor Sutherland said:


> AVC, is there a way to tell how much 120F water you in those two showers? What we need to do this totally right is a totalizer on the DHW pipe of the water heater/indirect. avc has the oil numbers now if we can get the total gallons of actual hot water used. Anyone have an old water meter kicking around????? It would be as simple at calculating the needed BTUs for the termp rise of the water actually consumed divided by the oil used (timer on burner calculation. *All the rest is standby loss.* Boiler drafting heat up the chimney, jacket loss of boiler, jacket loss of indirect, loss from associated piping etc. etc. etc.
> 
> AVC, I'd do a heat loss calc on your house, I've followed your threads on backup, type of house you have, and the rest. 1.25gph is alot of heat, you do not need it for DHW as you have proven.
> 
> ...


 
Unfortunately I do not know how much hot water is used.  I do know my shower is 7 minutes long on average.  My wife's is similar.  We have our indirect set to 120F.  Shower head is a modern fixture.  That is about as far as I know for fact.  

Monitoring water volume is much more difficult than monitoring oil burner run time.

ac


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## TheMightyMoe (Sep 27, 2012)

Well said Taylor.

Electric water heaters have the benefit of having no-negatives to cycling off/on to maintain temperature, recovery begin instantly. Where as on a indirect, recovery begins at the call for heat (A 5* diff at minimum), and the boiler reaching 140*+.

Easiest way to monitor a shower, would be run it a minute into a 5 gallon bucket, and then you know your GPMs.


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## BoilerMan (Sep 27, 2012)

TheMightyMoe said:


> Easiest way to monitor a shower, would be run it a minute into a 5 gallon bucket, and then you know your GPMs.


 
But we do not know how much actual hot water is used..... There is cold mixed in too. Just trying tobe as scientific as we can here.



avc8130 said:


> Monitoring water volume is much more difficult than monitoring oil burner run time.
> 
> ac


 
This is very true, as we are all nerdy on here, someone needs to come up with a community water meter we can UPS it to each other to find out our actual useages.

Modern shower heads are spec'd at 2.5 gpm, but that is not real life either, as it's just an orface that flows 2.5 gpm at a given pressure, are all houses the same pressure?? Nope. For that matter, is the pressure consistent throughout the shower for us who have wells?? Nope.

I'm still for electric in the summer just for the sake of saving on the entire boiler system short cycleing, and extra soot associated with those 5-10 min runs. Drain the indirect in the summer and fill the electric and flop on the 30A breaker, enjoy not hearing the oil cycle in the SUMMER!

The thread quoted back on page 2 has lots of info on electric water heaters and their almost non-existent losses. New electrics are supposedly .94% efficient, only 6% jacket loss. I maintain, there is sugnificant loss from the top piping arrangement, olb boilermantes had bottom connections to minimize loss, but plumbers hated running their copper to the floor to hook them up ( I don't blame them, as a tradesman) but it was more efficient.

TS


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## avc8130 (Sep 27, 2012)

For what it is worth, I believe my indirect is a priority zone.

ac


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## velvetfoot (Sep 27, 2012)

That was my point, about cycling the boiler.

My water softener has a flow meter built in and I made an assumption of what percent would be hot water.


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## velvetfoot (Sep 27, 2012)

That was my point, about cycling the boiler.

My water softener has a flow meter built in and I made an assumption of what percent would be hot water.


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## fire_man (Feb 19, 2014)

According to this calculator and my electric/oil costs in MA, Oil is slightly cheaper.
I currently have a dedicated oil fired hot water heater.


Cost per Million BTUs


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## BoilerMan (Feb 21, 2014)

I think your 65% number may be high for a Bock water heater.  If you go back to the first page Dick Hill found an indirect setup to be 33% efficient.  Not sure of a direct fired, with that 6" flue right up through the tank..........

TS


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## fire_man (Feb 21, 2014)

This may be just advertising, but it's right off Bock's tech sheet:

"The popular Bock® 32E leads the industry in Energy Efficiency with a .63 EF rating and 170 gallons first hour delivery."


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