Savings on DHW for Summer

[avc8130]

I know a lot has been talked about with the cost of DHW during the summer. I have decided to document something in a slightly scientific style.

The situation:

1 wife (shower daily)
1 14-month old (bath every other day in a plastic tub)
1 me (shower daily)
Clothes are washed with cold.
Dishwasher is run every other day.
Ice maker is fed from hot water (don't ask).

The equipment:

40 gallon Bradford White standard electric hot water heater. No timers, no special wiring, no games.

The results:

I monitored the power used by the DHWH using a Dent Industries logger I borrowed from a buddy.

Over a 4-day period (to capture the "normal" routine) I averaged 6 kWhr/day.

My electric rate is easily estimated at ~$.15/kWhr.

So....average daily cost for DHW FOR ME is....$.90. ~$27/month.

Average value of 1 cord of wood in my area: $200. So...1 cord of wood would have to last 7.5 months heating DHW to "break even" (not accounting for the work/effort/wear and tear on boiler.

Use this information carefully.

ac

 

[infinitymike]

Very cool, or should I say hot.
Either way, its a no brainer.
$27 a month is nothing in the sceme of things.
As you know, I heat DW with the WG and an indirect SuperStor 40, all summer using FREE pallet wood.
I guess my cost would be:
the fuel and time used to get the pallet wood: 1 gallon of diesel $4.20 and 2 hours of round trip time including loading them into the garage. This is a once every 6-7 week thing. so you could say 120 minutes/49 days is 2.44 minutes a day and .0857 cents in fuel a day
The time to to fire up the burner each day: 5-8 minutes 1-3 times daily so 24 minutes max. At what rate per hour?
The cost of electric to run the burner and the circ pumps to charge the indirect, NOT yet monitored. Need to find a friend with a Dent Industries Logger.

All in all, I don't think it costs me to much to heat DHW.

 

[infinitymike]

Oh yeah, the feeling to touch, ignite and watch the Wood Gun burn daily.....PRICELESS!

 

[maple1]

Your $/month figure for electric is in the same ballpark as mine. I might be around $25/mo area. I think there are lots of people who way overestimate what it costs or would or could cost to heat DHW with an ordinary electric hot water heater - as long as attention was paid to detail when it was installed.

Last summer I didn't burn - this summer I am. Had some junk wood accumulate I wanted to get rid of. Next summer I might not again - who knows.

But if I was paying for wood, especially at $200/cord, I would no doubt not be burning it just for DHW right now.

 

[avc8130]

Your $/month figure for electric is in the same ballpark as mine. I might be around $25/mo area. I think there are lots of people who way overestimate what it costs or would or could cost to heat DHW with an ordinary electric hot water heater - as long as attention was paid to detail when it was installed.

Last summer I didn't burn - this summer I am. Had some junk wood accumulate I wanted to get rid of. Next summer I might not again - who knows.

But if I was paying for wood, especially at $200/cord, I would no doubt not be burning it just for DHW right now.

Attention to detail? My setup has NONE. No foam on the floor. No heat traps in the piping. No insulation on the pipes. No timer. NOTHING. Just a "standard" install. LOL

$25, like Mike said, is peanuts in the long run. My monthly beer budget is higher.

ac

 

[91LMS]

My monthly beer budget is higher.

that has to be more like a weekly figure!

 

[velvetfoot]

I added one of those Nyletherms to my 40 gallon tank. Alas, I have no Idea how much money I'm saving. It runs for an hour at a time. The noise doesn't bother me since it's in the basement, but that electric heater was so quiet I forgot to turn it off when I switched to oil for a while (to empty the tank)! We're talking months! There's something to be said for quiet.

 

[peakbagger]

My Solar hot water system has been up for 10 years, the pump runs off a solar panel so its all free from about May to October. If I had to do system now I would just add more PV panels and run a HPHW heater.

 

[avc8130]

My Solar hot water system has been up for 10 years, the pump runs off a solar panel so its all free from about May to October. If I had to do system now I would just add more PV panels and run a HPHW heater.

What did the system cost? May-Oct is 6 months. $180/year savings. If the system was <$1800...

ac

 

[Corey]

Seems reasonable. I've found sometimes its also important to take into account the overall amount of energy usage and how the bill is structured.

For instance:

I'm on natural gas hot water and during the summer, the gas water heater is the only thing consuming gas...furnace and gas fireplace pilots are out and all other appliances are electric. My gas bill is also $27-$30ish, so one might think if I could heat water for 'free' I'd save ~$30/month.

But the bill is actually about $25 worth of customer charges, pipeline maintenance fees, taxes, surcharges, environmental remediation funds, etc. So even if I use 0 gas, I still pay about $25/month in charges. Or I could have the gas shut off in the spring and pay a $150 deposit/connection fee. Not a viable alternative.

It's probably not as bad with electric considering the house likely uses electricity for a lot of other things and DHW is a much smaller percent of the bill. But it's always important to separate out what it costs just to be a customer from what it actually costs to buy the energy.

 

[flyingcow]

I would kind of like to see a full 30 or preferably 120 days of kw/useage. 4 days really isn't enough to get a accurate $$'s. Just my 2 cents.

 

[BoilerMan]

I would kind of like to see a full 30 or preferably 120 days of kw/useage. 4 days really isn't enough to get a accurate $$'s. Just my 2 cents.

My thoughts exactly. Also my electric rate is .17/kWh, slightly higher, but there are more showers. It really depends on how many gallons are used. I think avc's info is a good ballpark. But I'd estimate an "average" electric water heater costs in the $40-50/month range. But with one single old lady who takes a 5min shower/day and washed dishes once a week it may cost $15/month for Electric resistance HW. Standby losses being the majority of that number. A commercial 80gal 5500W electric used for cleaning would likely cost much more with relatively the same standby loss.

Leave for a week, data logger connected and measure real-world standby losses, the rest is actual usage. Also calcium/lime buildup can play with the operating nunbers.

TS

 

[hobbyheater]

DHW; 1 lbs of wood gives me roughly 6 gallons of hot water.
1 cord of wood ($40.00 per cord) supplies our hot water needs from the beginning of May to the end of September.
Summer time is at least 4 showers a day, dishwasher 3 times per day,1 large load of laundry hot water wash per day.
Electric rate $.07 KWH


https://www.hearth.com/talk/threads/did-an-exeperiment.129436/

 

[peakbagger]

What did the system cost? May-Oct is 6 months. $180/year savings. If the system was <$1800...

More that $1,800, I think I was all in around 3K At the time I installed it I had tankless hot water system on oil so I had to run the boiler for 5 months year just for hot water. I figured 1 gallon a day to heat my water (and my basement). At $3 per gallon that's $450 a year or $4,500 for 10 years. I also get some benefit from preheating my hot water in the colder months of the year

 

[avc8130]

I would kind of like to see a full 30 or preferably 120 days of kw/useage. 4 days really isn't enough to get a accurate $$'s. Just my 2 cents.

I don't disagree. I just polled the logger last night. 10 days logged now. Still tracking at ~6/day.

The logger is still running, but my use is VERY consistent.

ac

 

[avc8130]

My thoughts exactly. Also my electric rate is .17/kWh, slightly higher, but there are more showers. It really depends on how many gallons are used. I think avc's info is a good ballpark. But I'd estimate an "average" electric water heater costs in the $40-50/month range. But with one single old lady who takes a 5min shower/day and washed dishes once a week it may cost $15/month for Electric resistance HW. Standby losses being the majority of that number. A commercial 80gal 5500W electric used for cleaning would likely cost much more with relatively the same standby loss.

Leave for a week, data logger connected and measure real-world standby losses, the rest is actual usage. Also calcium/lime buildup can play with the operating nunbers.

TS

I can see the standby losses easily. We don't use ANY hot water from the time my wife showers in the morning until the baby gets a bath at night. This is a period of ~12 hours. I have the logger set to take the following data every 5 mins:

Peaks (min and max)
Average (average over the 5 min period)

I don't remember off the top of my head how often it runs when we aren't drawing. I can check tonight.

ac

 

[avc8130]

DHW; 1 lbs of wood gives me roughly 6 gallons of hot water.
1 cord of wood ($40.00 per cord) supplies our hot water needs from the beginning of May to the end of September.
Summer time is at least 4 showers a day, dishwasher 3 times per day,1 large load of laundry hot water wash per day.
Electric rate $.07 KWH


https://www.hearth.com/talk/threads/did-an-exeperiment.129436/

1. $40/cord? HOLY CHEAP!
2. $.07 KWH? HOLY CHEAP!
3. You run your dishwasher 3x per day? How small is this dishwasher?

ac

 

[avc8130]

My thoughts exactly. Also my electric rate is .17/kWh, slightly higher, but there are more showers. It really depends on how many gallons are used. I think avc's info is a good ballpark. But I'd estimate an "average" electric water heater costs in the $40-50/month range. But with one single old lady who takes a 5min shower/day and washed dishes once a week it may cost $15/month for Electric resistance HW. Standby losses being the majority of that number. A commercial 80gal 5500W electric used for cleaning would likely cost much more with relatively the same standby loss.

Leave for a week, data logger connected and measure real-world standby losses, the rest is actual usage. Also calcium/lime buildup can play with the operating nunbers.

TS

You can estimate all you'd like. You could also collect data.

Use is use. Regardless of the fuel source, the more you use the more fuel you will need. The electric is 100% efficient, so at least the inefficiencies don't pile up as the use goes up.

Standby losses are going to exist in any system.

ac

 

[Mushroom Man]

Last year I cobbled together two (2) prototype solar collectors from scrap (left-over pex, recycled insulation, scrap steel roofing, an old DHW tank from the dump, patio doors from the dump etc). They look horrible but are not highly visible.

My system is a seasonal hookup to avoid burning in summer. In winter the boiler provides lots of hot water at negligible cost. The boiler is in the attached garage so it gets too hot for my liking in summer and the storage tank is in the basement under our bedroom.

The first collector uses a 50 gallon black DHW tank in an insulated box with a glass top and front. Two doors cover the top and front of the box at night (but most of the time I forgot to close them). Water to the indoor DHW tank (oil-fired but no oil is used) is intercepted by this "breadbox" bulk tank and heats up in the sun. No pumps. It is pressurized from the house plumbing.

The second collector, an active collector, circulates water to my sidearm on the DHW tank. The collector itself is serpentine loops of PVC and pex under glass. The sidearm was already attached for heating DHW with the boiler. It works on my house circulation pump in the boiler system. The active collector becomes the boiler in essence. A few Tees and valves were added to the system and a snap switch controls the pump on /off .

Bottom line. The two collectors heated roughly 100 gals of water but not enough for a comfortable shower. On hot sunny days it got near 100 degrees. I showered but the girls grumbled and waited for the boiler heated water. I say it averaged 85 degrees with highs to 100. Not bad considering our well is deep and cold (45-50 degrees).

Some, like my wife and daughters, would consider my efforts last year a failed experiment because the collectors did not get hot enough for showers.
But I thought the two collectors made a great preheater. This year I added a Stiebel Eltron 12 kW tankless electric water heater ($371). With preheating, I likely could have gone smaller (lower kW) but I didn't want to risk failure for $40 additional bucks. I had envisioned just boosting the bathrooms with the tankless but decided to go whole-house. That was the right choice.

Everybody is happy. My wife thinks I am handy to keep around. We cannot run out of hot water and it is (likely to be) much cheaper than conventional resistance heating and oil heating due to the preheating and no standby losses.

The tankless is new so no data is in yet but I am optimistic. The tankless unit can be turned off except for showers and that is OK with the girls; but I doubt that it will be necessary to turn the tankless heater off.

If my calcs are accurate or even close; the cost of operation will be trivial and the jacuzzi tub will be a REAL treat instead of a money pit.

 

[hobbyheater]

1. $40/cord? HOLY CHEAP!

Just the expense for gas, saw chains, etc!
Wood is free road side waste, 17 kilometers a round trip per 1/2 cord load.

2. $.07 KWH? HOLY CHEAP!

60 years ago we had a rarity in Government that planned for the future and built a bunch of Hydro Electric Dams so Cheap electricity today, but if you use over 700 KWH per month, the rate goes to $.11 KWH, so another good reason to save on electricity where possible!

3. You run your dishwasher 3x per day? How small is this dishwasher?

Standard size household dishwasher and but no Microwave oven and no prepared foods. I get a lot of pots, pans and bowls dirty doing food prep!
[/quote]

 

[BoilerMan]

You can estimate all you'd like. You could also collect data.

Use is use. Regardless of the fuel source, the more you use the more fuel you will need. The electric is 100% efficient, so at least the inefficiencies don't pile up as the use goes up.

Standby losses are going to exist in any system.

ac

All I'm saying is that you need TIME to measure real standby loss. Time, as in at least a week, discount the first day as the heater will be recovering or on the verge of recover from a previous draw.

When I was first married, we lived in a 20x24 apartment which was a free standing two car garage converted to living space. Electric 30gal water heater, our bill averaged $60/ month in the summer. We both worked and were not there during the day. I built our current house in 2009, same utility provider and same electric rate, same washer, same dryer, same wife etc etc. My summer bill (when burning oil for DHW) is $20-25/ month, and our house is MANY times bigger. I can't collect data now as I don't have electric resistance hot water, I'm just saying that we may use more water than you do. As an HVAC electrician, I monitor these types of things.

TS

 

[jebatty]

My wife and I, no baby, but frequent adult family guests with children, average 100 kwh/month for DHW with standard resistance HWH, off-peak rate at about $0.05/kwh = $5/mo for electric, $0.17/day. Was twice that before insulating, heat traps, etc. While wood provides 80-90% of space heating needs, would never make sense to change our DHW system.

 

[avc8130]

All I'm saying is that you need TIME to measure real standby loss. Time, as in at least a week, discount the first day as the heater will be recovering or on the verge of recover from a previous draw.

When I was first married, we lived in a 20x24 apartment which was a free standing two car garage converted to living space. Electric 30gal water heater, our bill averaged $60/ month in the summer. We both worked and were not there during the day. I built our current house in 2009, same utility provider and same electric rate, same washer, same dryer, same wife etc etc. My summer bill (when burning oil for DHW) is $20-25/ month, and our house is MANY times bigger. I can't collect data now as I don't have electric resistance hot water, I'm just saying that we may use more water than you do. As an HVAC electrician, I monitor these types of things.

TS

Why can't you monitor? Monitor the on-time of your oil burner and multiply by the nozzle flow rate. I did it before I ripped out my oil burner.

I can save you the trouble...for just 2 people (baby didn't exist yet) we rocked through 1/2 gallon of oil daily. At TODAY'S price in my area, that is $1.60/day. Call it $48/month.

ac

 

[maple1]

We went though more like 1 gallon a day for DHW with the old tankless coil setup (150 gallons lasted 5 months). What a piggy that thing was....

 

[infinitymike]

Ugh, I used to go through 200 gallons from May to Oct.
33 gallons a month $116

SOOOOO, glad to be burning wood.