For non oil burners - how to get hot water

[woodgeek]

My electric company reports that a 20 gal tank will cost $77 per month to run. Electricity is expensive in NH.

Here's your problem, you're hung up on this.

A 20 gallon tank costs nothing to run if you don't use it. It can certainly cost more than 77$ if you overuse it. The cost to heat X gallons of water is the same nomatter how big the tank is. A btu is a btu, a watt is a watt.

When you say heat pump are you considering a heat pump water heater? Those are actually pretty attractive for basement installs where you also need humidity control.

Highbeam

I know I'm hung up on this. Mostly because nh has high electric costs. People I known that have electric HW tanks, want to change them because of costs. I understand that if you don't use water, it will be fairly cheap, but I'm assuming I'm using water.

If I'm using .87 gal of oil a day with an 86% efficient boiler, I'm putting 105,000 btus into heating water. Granted that some of these btus are left over in the boiler and lines leading to the HW tank, I just don't know ho to figure this amount out.

.87 * 30 days * $3.50 = 91.35 per month for oil

1 watt-hr is 3.41 btus

105,000 / 3.41 = 31kwh

31 khw * $.17/kwh * 30 days = $158.00

My left over heat would have to be 43% of the total used. I can't imagine it is that high. I have a low mass boiler that tries to dump all extra heat into the last zone asking for heat.

If my numbers are wrong, please let me know.

Thanks

Your calc assumes that your elec tank would have the same standby losses as your oil system. You are correctly comparing the cost of oil and elec BTUs, but as we said before we think you are losing 2 BTUs to standby losses for every one that goes to delivering DHW. So, if a conventional elec tank used 1/3 the BTUs, its $53/mo and a HP unit at a conservative seasonal average COP=2 would use half THAT, or $26/mo.

IOW, the $77/mo for a tiny tank number from your utility is utter BS.

 

[woodgeek]

If you want to go crazy, measure the gallons per minute in your shower, estimate the minutes per day, and assume a Delta temp of 60°F (45 supply to 105 shower). Take the product * 8 lbs/gallon and that is your BTU/day for showering. IF you are doing all your laundry in HOT, stop, and worst case by different detergent. Add 20% safety factor to the total for dish/hand washing.

Most households use ~10-20,000 BTU/day/adult. See where you come in. Your calc is correct, if you come in under ~60,000, implying less than 60% delivery eff, you come out ahead with **conventional electric**. For a HP system, it will run conventional in the winter (making the previous calculation useful re 'switching' back to a boiler indirect in the winter). In the summer it will have a COP of 3-4 and thus cost equivalent to $1.25-$1.50 oil on a BTU to BTU basis AND give you free dehumidification. That is so cheap that even if (gasp) the price of oil collapsed, i.e. $2, you are still saving money, and if the cost of oil goes above $4 you can save plenty of money in the winter too.

 

[EJL923]

$77/month for hot water seems awfully high. We have a 50 gal hot water heater. I don't know what the hot water heater pulls, but our monthly bill fluctuates from $100-$120/month depending on the time of year. Our electric with everything added on is about 0.18/kwh. I also like the fact that it is virtually maintenance free. My oil fired furnace only gets used for the occasional supplemental heat.

 

[maple1]

A Geyser can be hooked up very easily to almost anything. I have coils in my oil burner, I think I could hook it up to my coils and it would keep my oil burner warm all summer quite cheaply. Maybe even add on a cheap electric hot water tank for more storage & back up if I wanted - they seem to have lots of possibilities.

 

[Highbeam]

If I'm using .87 gal of oil a day with an 86% efficient boiler, I'm putting 105,000 btus into heating water.

If my numbers are wrong, please let me know.

Thanks

That's the only disconnect I can see. You are not putting 105,000 btus into the water, you are putting 105,000 btus into a machine to heat water and only getting a portion of those btus back as hot water. Your 86% efficient boiler is only 86% efficient when it is at steady state being used hard for a long period.

With an electric resistance heater you get nearly 100% of the btus actually delivered to the water.

17 cents per KwH is not expensive. You have relatively cheap power.

I really hope you go for the HP water heater since it is better than 100% efficient. Much better than 100% and then you get reduce the load on the dehumidifier for even more savings.

 

[Jack33]

I was in a similar situation as the OP. I calculated I was using .75 gallons a day just to heat DHW with my oil fired boiler. I have a 40 gallon DHW storage tank off the coil controlled as a zone by the boiler.

I choose to install a new 40 gallon electric hot water heater.

I am in NH and have PSNH as my electric provider. Before the electric water heater, my bill was about $100 a month year round (excluding July/Aug do to AC useage). After I installed the water heater my bill is still about a $100 a month. 2 adults in the house and we don't conserve hot water other than washing clothes in cold water only. I don't sacrifice hot showers, dishwasher, etc. I have the temp on the water heater set at 120. I figure the boiler uses a fair amount of electric running the gun, stats, controller, 2 circulator pumps, etc.

I installed the electric water heater after my boiler storage tank. So regardless of the season, inlet water flows through the coil, into storage tank, and into the electric water heater. So during the winter, I basically have 80 gallongs of DHW in storage. All I have to do is kill power to the boiler and to the storage tank which has a t-stat on it.

I installed this Dec. 21 of 2010. I have about $600 into the electric heater, copper pipe, 50Ft of wire, ball valves, exp tank, etc. I figure from April-Nov oil useage was about 200 gallons of oil prior to install. 200 gallons @ $3.50 is $700. The pay back period was less than year.

The estimate of $77/per month heating water with electric is way off. I would guess I spend about $1 a day to heat water, but I am saving $1 a day in electricity by turning off the boiler.

 

[wannabegreener]

Had a solar installer come in today to give the house a look over. I wanted to see what they would come up with for a price. While he was here, we talked about solar dhw, full electrical solar, and a heat pump. They sell stiebel eltron heat pumps for hot water. Looks like you can get them with 2 coils in case you wanted to do solar. I'm waiting on prices for everything. They are all very interesting and I hope to be able to shut down my boiler in the summer.

One thing I don't quite understand is the 'First hour rating". On the heat pump, the first hour rating is 76 gals, but it is an 80 gal tank. So, if you have 80 gal of hot water and you start using it, if the rating is only 76, does this mean that as the cold water enters the tank, obviously it mixes with the hot, but that the heat pump can't even recover enough to use the complete 80 gals? Is that normal for a heat pump?, what about other fuel sources like pure electric, oil, or gas? I thought I finally understood what this first hour rating was all about.

My roof ridge goes N/S so not optimal for anything solar. They can do it by lifting/tilting the panels for hot water.

 

[woodgeek]

Had a solar installer come in today to give the house a look over. I wanted to see what they would come up with for a price. While he was here, we talked about solar dhw, full electrical solar, and a heat pump. They sell stiebel eltron heat pumps for hot water. Looks like you can get them with 2 coils in case you wanted to do solar. I'm waiting on prices for everything. They are all very interesting and I hope to be able to shut down my boiler in the summer.

One thing I don't quite understand is the 'First hour rating". On the heat pump, the first hour rating is 76 gals, but it is an 80 gal tank. So, if you have 80 gal of hot water and you start using it, if the rating is only 76, does this mean that as the cold water enters the tank, obviously it mixes with the hot, but that the heat pump can't even recover enough to use the complete 80 gals? Is that normal for a heat pump?, what about other fuel sources like pure electric, oil, or gas? I thought I finally understood what this first hour rating was all about.

My roof ridge goes N/S so not optimal for anything solar. They can do it by lifting/tilting the panels for hot water.

Ok, the water in a tank stratifies, hot on the top, cold on the bottom, which is why the heat is delivered to the bottom. As the cold comes in the bottom, the hot leaves out the top. Without any added heat, the FHR will be less than the volume because of 'dead volume'...hot water that can't leave, or imperfect stratification--it will be close anyway. Compared to all fossil heaters, all elec heaters will have slower recovery. 110 kBTU/h = 30 kW. With an electric heater, that would be 135 amps at 220 V! Thus, while a fossil heater could regenerate the water in 30 minutes, a 5 kW element (typ) will take 6x longer, or 3 hours. Since the heat pumps are typically sized around 0.5-1 ton (6-12000 BTU/h), they will take 10-12x longer, or 5 hours to recover. Most HP systems have a nice controller that allows you to use both heaters ('hybrid' mode) to get faster recovery, e.g. when you've got a houseful of guests, at a slight loss of energy savings.

I also looked into solar, and was surprised when the equivalent to FHR worked out to be just 50% of the tank volume. IOW, the backup usually comes on when the tank is half hot and half cold, so the tank can only absorb solar heat into its bottom half. Equivalently, you need a tank which is ~2x your daily usage to avoid blowing a lot on backup.

As I have said elsewhere, the quote for commercial solar DHW was higher than a HP system even with a 70% rebate, and if I used the (conventional elec) backup for 40% of my seasonal needs (likely looking at my low winter solar resource), then the (electrical) operating costs were nearly the same!

Of course, the lowest operating costs would be for a solar DHW + HP backup, but by then I would have >$15k of hardware tied up to get save a few hundred $$ a year.
Even worse, the HP wouldn't work in my application in the winter (semi-conditioned install), so there would be not advantage to having both.

 

[frizman86]

I have read all the way through this thread and boy am I confused. I currently am running my hot water heater on Propane at $2.50 a gallon. it is costing me around $50 a month. I switched from a propane fernace to a pellet stove. The furnace + hot water heater cost me $500 a month for LP. The pellet stove I am factoring in $100 a month for 4 months a year for two years to cover the install cost, and $125 a month in pellets. So my Propane bill is around $50, and pellet heat bill around $225 a month. So I am saving $225 a month. $50+$225=$275. Electric here cost me $.15 per kw, and acording to the Whirlpool website there most effeciet 50 gallon ( I figured that was average) uses 4622 kw a year. So .15 x 4622= 693.3 for the year then / by 12 and it is $57.78 a month. Now that is for me. it looks like the average here is .10 per kw so even then it would be $38.51 a month. So for me propane is cheaper, then electric. This is all asuming they are not lowering the numbers a little to make people want to by their product. Were I am confused is how is it only making your bill around from $5 to $16 more a month. You guys must have some very cheap energy. These things use 4500 watts per hour. thats 4.5kw or at even .10 cents per kw thats .45 cents per hour they are running. now I know they dont run all the time but even then if it is running say 8 hours total in a day. .45x8= $3.6 a day X just say 28 days a month is $100 a month.

I have a wierd feeling if you were to put a energy monitor on your house and and monitor it for just a day with no change, Then shut the breaker off for the hot water heater for a day, you will then see a big differance. My weifes parents own a electric hot water heater that is 5 years old. Thier bill was $112. somthing for the month of Dec. and they are running a wood burning stove instead of a fernace.

Our bill for the month of Dec. Was $55. something. And that is running, normal light usage/TV (10w CFL's and 32 inch LCD TV), a fridge (high efficentcy got summer 2011), a stand alone freezer (15 years old), pellet stove , 55gal salt water aquarium, range, dishwasher, well pump, and dryer. It is a 2,000 sq ft home with two adults, and .15 cents per kw. I guess I just am not seeing were it is so cheap to run. Even if it were to only cost $38 a month it still would not justify buying a $1500 electric hot water heater, with a $12 a month savings it would take me 10 years to recoupe the money back.


For me personaly I am trying to find a way to use the pellet stove or pellet stove vent pipe to keep the hot water heater hot in the winter and do away with propane altogether for 3-4 months.

 

[woodgeek]

Your numbers make perfect sense for you--your propane and elec are similar in cost on a BTU basis. The difference is in using a hydronic boiler to heat your DHW using a tankless coil. The standard oil-fired boilers out east have a really large standby loss, 0.5-1.0 gallons oil/day. At $4/gal that is $2-4 a day for standby loss, before you even think about the BTUs needed to heat the water. In my case, I am burning ~300 gallons oil/year, just for DHW, works out to ~$100/mo. Your point is well taken...I could get a propane water heater and have a good operating cost.

 

[frizman86]

I Hope I did not come across as trying to push propane more the electric. I am just trying to wrap my head around how it is only making other peoples bills go up a few dollars.

 

[nate379]

The standby loss on any modern water heater with a tank isn't much. Something around 1/2* per hour. Tank vs tankless, there isn't that much benefit IMO.

I have shut mine down before to do work on the boiler and even after a couple days there is still fairly hot water, provided I am conserving the water.

I'm not one to stand in the shower for long either though, pretty much a 15-20 min chit/shower/shave guy... as I'd imagine most of us are.

 

[woodgeek]

I Hope I did not come across as trying to push propane more the electric. I am just trying to wrap my head around how it is only making other peoples bills go up a few dollars.

No problem. You just have to wrap your head around ~5 million oil-fired systems in the US that were designed for and made perfect economic sense when oil was $1 gallon, and which now make so little sense at $4 that almost anything you replace it with (e.g. rabbits on treadmills eating organic micro-green arugala) will have a nice ROI.

Something I have thought about....we spend a lot of time here talking about (simple) ROI or 'payback'. Just b/c something has a quick payback doesn't mean its the best solution when changing/upgrading a system. One really should think about cost of ownership, like install cost + operating cost over a time span of your choosing (i.e. 10 years). In the case of this thread, the OP and any oil burner can make a long list of alternatives that have great payback, but the fastest payback does not equal the lowest cost of ownership.

It is my contention that an electric HP system will have to lowest cost of ownership over ~10 years, with the exception of a NG-fired system that many of us do not have access to. Specifically, while more upfront than a conventional elec tank, the lower operating cost makes it come out ahead. While a solar DHW system has even lower operating costs, it isn't all that much less if the electric backup provides 30% of the BTUs, so it is hard to recoup the initial outlay unless you build it DIY.

I am not an electric chauvinist. I just don't have propane now or a great place to put a tank. The propane people currently share the oil folks' pain on a cost per BTU basis, but for a well insulated tank-type propane fired DHW system (oil equivalents are available but seem rare to me), the lower standby means that they are not useless. And since propane is a byproduct of gas fracking, it is possible that expanded fracking operations will eventually drive down the cost of propane, as it already has for NG. Or it may not.

 

[Highbeam]

And where in the world must you pay 1500$ for a 50 gallon electric water heater?

 

[nate379]

I'd be interested to know what the cost per month is on a std nat gas water heater vs a boiler mate/indirect fired water heater?

During heating season it's probably not much extra to heat DHW off the boiler since it's likely already running, but in the summer I have to wonder what kind of heat loss from the pump/piping and actual boiler. My setup is a cold start boiler too so it has to heat 60-70 water in it to 120* just to get to the point of warming the water too.

I do know summer use for natural gas runs me around $30-40. 2 people and kitchen stove and dryer also are gas.

 

[woodgeek]

And where in the world must you pay 1500$ for a 50 gallon electric water heater?

(broken link removed to http://products.geappliances.com/ApplProducts/Dispatcher?REQUEST=SpecPage&Sku=GEH50DNSRSA)

 

[Highbeam]

Don't be silly.

(broken link removed to http://www.homedepot.com/Plumbing-Water-Heaters-Residential/h_d1/N-5yc1vZbqowZ1z109sqZ1z11t6dZ1z11zlcZ1z0yv00/R-100034997/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053)

 

[woodgeek]

In 12 years, I will have to buy two of those, and spend $8000 on electric, versus 1 geospring and $3000 in electric. Don't I come out $4000 ahead over that period?

Maybe your kWh out in WA are basically free, mine aren't.

 

[Highbeam]

The point is that you need not spend 1500$ on a tank heater unless you want to. Even the 250$ water heater will be much cheaper than the oil indirect which is the topic of this thread.

I am becoming a fan of the HP water heater if you have 1500$ to spend and can live with the noise.

 

[woodgeek]

The point is that you need not spend 1500$ on a tank heater unless you want to. Even the 250$ water heater will be much cheaper than the oil indirect which is the topic of this thread.

Aaah. Agreed.

 

[greythorn3]

as much as i hate our on demand hw heater it cut our gas usage by 1/3 over the tank one we had before.

 

[wannabegreener]

I'm going to guess that the on demand won't work for me because of well water. I had it in my old boiler when I bought the house and the previous owner said that the "coil" or whatever it is needed to be replaced frequently. This was because of the build up of minerals on the inside of the coil. Because of this, I'm going to assume that the geyser won't work either.

I got my quote for solar and it claims that I will only save 120 gals of oil per year. OUCH At about 3.50 per gal, it would take about 14 years to pay this back. That doesn't include the electricity to run the pumps so it will probably be closer to 15 years.

Anybody use the steible-eltron heat pump for hot water? The same company that quoted me for solar sells that brand as well and gave me a rough quote of $4000-$5000 to install. I can find the same unit on amazon for about $2000. I can't believe it would cost $2000-$3000 for installation costs plus pipe, elbows, etc.

Still trying to figure this out. I really appreciate all of the comments and experience in this thread and forum.

 

[woodgeek]

I was looking at the80 gallon AO Smith:
http://www.hotwater.com/water-heaters/residential/hybrid/voltex/
which seems to be re-labeled and resold by a number of other vendors. I have plenty of space, and wanted a higher FHR than the 50 gal GE unit.

I would think that a local plumbing contractor would be cheaper than a top $$ solar company.

 

[woodsmaster]

I have a famly of 5 (3 girls lots of baths ) We used to use elec. WH to the tune of $75.00 / month. I now use
a wood boiler and the money save on hot water would buy 2/3 of my total wood heating home shop and dhw.
It was a large investment, so It will be a few years before I see a return.

Woodmaster, what are you using in the summer. I can't imagine you are using your wood boiler in the summer.

Sorry for the slow response. Been a while since i've looked at this thread. I will heat my hot water with the wood boiler
this summer. I have to fire once every 5 days for hot water. My wood is free other than time and a little gas and oil for
the saw. I hope to build some solar panels for summer water somtime in the next couple of years and tie into the
boiler storage.

 

[begreen]

I am looking at the GeoSpring system. For those who what installed one, do you notice the heat loss in the basement? If so, by how much? How difficult was the install? Did you put in a new storage tank or did you use your old electric(?) tank?

The Geospring is an integrated unit, HP + tank. You might be thinking of the 'AirTap' retrofit system... The all in ones have a significantly better COP than the retrofit approach.

So I have now looked at the GE unit too. (Thanks for the HD link Highbeam!) One question I have is about the recovery time is for a full tank? Is it slower than resistance electric or about the same? Or does it just go to resistance heating for rapid recovery? How noisy is it? The spec says 58db which seems a bit high. That maybe ok for a garage but I am not sure I like that for a basement or closet installation.

PS: Nevermind, I just found this review on GE's site for the GeoSpring. The more I look, the more bad reviews I am finding for these hybrid heaters.

http://blog.yagelski.com/2009/11/ge-hybrid-water-heater-does-heat-pump.html