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Simple solution? Oil fired FHW

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by babalu87, Nov 8, 2007.

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  1. babalu87

    babalu87 New Member

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    The only time my oil burner runs if for hot water. The house is heated 100% with the wood stove.
    It is a tankless system with an expansion tank and we have baseboard heat.

    Would it be more economical to have storage for the hot water? The boiler runs during the day just to maintain hot water and then runs again for showers etc.
    I am planning building something solar this winter or at least getting it laid out and finish gathering materials but there has to be a fairly simple solution to at least assist the boiler in heating the hot water. As simple as a well insulated 55 gallon plastic barrel?

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    Offhand, I'd say you'd be ahead to shut off the boiler and get an electric hot water heater, or buy an oil-fired hot water heater. I don't think using a boiler exclusively to heat DHW is a good way to save money.

    But I'm just guessing. This would be a good one for castiron, who seems to have his act together where things electrical are concerned.

    Also, babs, you might try posting your question over at heatinghelp.com. They have a bulletin board called The Wall where HVAC pros answer homeowner questions. I'd be interested in their replies; you might get some diversity of opinion, but all of it will be well informed. They know a lot about solar as well.
  3. babalu87

    babalu87 New Member

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    Thanks Eric for that site, I posted and will copy/paste replies here.

    When we built the house oil was .85 a gallon and propane was cheap too.
    I really should have addressed the hot water when I installed the wood stove.
    Tankless hot water is pretty economical when heating a house with the same system but it is like pissing into the wind now. Than damn thing runs all the time because the basement is so cold.

    We have a propane dryer and oven, propane is at $2.90 a gallon on the latest bill.
    By comparison electric is under 9 cents per KW
    I think the way to go for us is with an electric hot water heater, I just need to figure out if it should be a tanked system or tankless.
  4. titan

    titan Minister of Fire

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    For my money I'd install a 40 gal. electric tank.The new 'smart' tanks use a rigid foam for insulation, cuts down on standby heat loss better than the old fiberglass insul. tanks.If the tank goes in the basement get it up off the concrete floor with 2" Sm styro. underneath.
  5. babalu87

    babalu87 New Member

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    Titan, that is the route I think we will go.
    I was thinking of building some type of shelter for it as well to help insulate it from the cold of the basement.

    Hell, with tax credits etc I can get a HW heater for about the cost of filling my oil tank.

    I'd like to know approximately how much juice a 40 gallon electric heater uses for 4 people one dishwasher and all laundry done with cold water.
    There must be somewhere to figure out how often it will be"running'
  6. Nofossil

    Nofossil Moderator Emeritus

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    I had the exact same situation, but my boiler needed a heat storage tank for efficient operation. I left my indirect oil-fired hot water heater in place, but my domestic water is heated in several different ways:

    1) The cold well water runs through a coil in the heat storage tank before going into the bottom of the DHW tank.
    2) The storage tank is heated by solar in the summer and wood in the winter.
    3) If the storage tank is hot enough and the DHW tank needs heat, I circulate water from the storage tank in place of water from the oil boiler
    4) If the wood boiler is operating, it heats (actually, superheats) the DHW tank.
    5) If the oil boiler runs for any reason. once the demand is gone any extra heat in the oil boiler goes into the DHW tank.
    6) Finally, if all else fails, the oil boiler heats the DHW just as it did originally - just nowhere near as often.

    I kept the oil because it's also a backup to heat the house when we're away.

    Here's a link to a writeup on my hot water system - I think you've already found my writeup on my hot water solar panels.
  7. n1st

    n1st New Member

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    Funny, I was going to post this exact question. I'm in the same boat but my electricity is $.21/kwh, so I guess I'm in a worse boat.

    Just started researching tonight. Have you looked at the on-demand propane/gas/oil water heaters? They do look interesting. Anyone have one of these and can comment on them?
  8. Nofossil

    Nofossil Moderator Emeritus

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    My brother has a propane model and loves it. It does have some limitations if you want to combine it with other energy-saving concepts such as preheating your hot water with wood or solar. The on-demand units supply a fixed amount of heat. If you try to use preheated water, you run into overtemperature/underflow problems. Topic for another post....
  9. cbrodsky

    cbrodsky Member

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    I would suggest an electric tank is worth thinking about depending on your local electric rates.

    You will hear a lot of fairytale stories about how tankless heaters will save you a fortune. It is smoke and mirrors IMHO compared to a well insulated tank sized right for your house - you'll never recoup the capital cost, and they're bad for the grid. And electric rates are getting close to heating oil these days.

    1 kWh of power = 3412 BTUs.
    1 gallon of oil = 139,000 BTUs.

    With electric, all the energy goes right into the water tank. Your oil burner at best is probably doing about 75% efficiency for transferring heat, so out of that gallon, you probably only get 104,250 BTUs. This is equal to 30.6 kWh. If you're paying about $3/gallon for oil, and $0.10/kWh for electric, then the two costs look pretty similar.

    Next, you have to consider standby losses - an oil boiler will lose a lot more heat while it sits idle as compared to a well insulated electric tank. I have not seen as much good data on this, but some studies claim overall boiler efficiency for tankless coils can drop to 50%. This further tips the scale to make electric look better.

    You can run the math on your power rates to see how it works for you to help decide how close the options are - a couple years ago it would be crazy to consider, but now it's not such a bad idea.

    In my case, I am using solar to partially heat the water this time of year and using electric to finish it off. This is letting me keep my boiler off much later than normal. But once I fire up the boiler, I'll turn off the electric and use oil to finish heating the water. I paid $2.39 this year for my tank of oil and electric is about 0.12 so easy decision IF I have to have the boiler on for heat use anyway - at that point, I'm already paying the standby loss penalty for home heating needs.

    -Colin
  10. cbrodsky

    cbrodsky Member

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    ps - a local outfit was offering tankless gas/oil water heaters installed for about $3,000. For that price or incrementally more, you could probably swing a solar installation in NY State after tax credits - much much smarter investment than something that will still require expensive fossil fuel to run. And in the case of oil, far more maintenance than a drainback solar HW system requires.

    -Colin
  11. babalu87

    babalu87 New Member

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    Nofossil, do those solar panels sit right on the ground?
    Could they be better served sitting on some rigid foam insulation?
    Are you running glycol in the panels?

    I am looking to go with a very similar system, especially one that can be worked on and serviced at GROUND level.

    Nice system, now I see how you got that username ;)

    EDIT
    How are those pool heating panels made? Could they be copied with access to the right materials?
  12. Nofossil

    Nofossil Moderator Emeritus

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    The glazed panels are right on the ground. They have fiberglass insulation internally behind the collector surface. The pool heater has a sheet of foil-faced foam board under the top 8' - I'll add more when I get around to it ;-)

    I run water in the system, unpressurized. I have a vented reservoir under the deck above the top of the storage tank. Five reasons for not running glycol:

    1) It's expensive
    2) I'm still dealing with leaks in the panel plumbing
    3) The sun angles are pitiful in fall and winter - not much heat to be had.
    4) It's a slightly higher viscosity, which would reduce flow.
    5) It's toxic

    My solar season ended in mid-October - two days before my first wood fire. Once the wood boiler is going, there's no need for solar anyway. Half an hour of wood boiler is more heat than the solar panels could generate in a day, and the tank temps are so hot that the solar panels couldn't add any at all.

    The pool panels are extruded polyolefin. Polyolefin as far as I can tell means 'plastic made of whatever we had lying around'. I bought mine off of eBay for $140 including shipping. I contacted the manufacturer, but they had decided to develop their own solar hot water system and were not interested in talking to me. Haven't seen it yet, though.
  13. babalu87

    babalu87 New Member

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    Thanks for the input. Whatever system we adopt I will need to go with glycol. If anything, I want it to at least warm the storage tank to take the load off the water heater during winter and it should provide all the hot water we need during the summer season.

    I feel a little stupid using the boiler for hot water three seasons running now, what a waste. Its a GREAT way to heat hot water when the boiler is running for heat but other than that its a waste. Especially during heating season.

    I already have glass for collectors and I think refrigerator tubing encased in a well insulated panels with everything but the glass painted black will be a start to the system anyway. I plan on having it so I can change the pitch for Summer/Winter sun angles.
  14. Nofossil

    Nofossil Moderator Emeritus

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    Sounds good. There are a couple of other considerations. If you're going to use a pump, you will need to control the flow rate. Too fast reduces the temperature of the water that you get out of it. A small amount of hot water is more useful than a lot of lukewarm water.

    If you're using thermosiphoning, think very carefully about bubbles - they are your enemy. They will collect at any high spot and stop flow. Also, take pains to ensure there are no restrictions. The pressure differential that makes thermosiphoning work is extremely small. Lots of parallel flow paths is much better than a smaller number of paths laid out in series,

    Lastly, plan for high temperatures. I've actually boiled water in my panels - see comment on bubbles above. You can burn yourself, and plastic fittings will fail. You will also want to install a tempering valve to ensure you don't get scalding water out of the tap. You also have to plan how to dump excess heat if you don't have a really large storage tank. I heated my 880 gallon storage tank to over 150 degrees with the panels that I have. A smaller tank could lead to boiling in the panels.

    Good luck - post pictures and results!
  15. thephotohound

    thephotohound New Member

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    I am also running an oil fired boiler just for hot water, and it's driving me up a wall. My thought was to also go electric with a super-efficient 40-60 gallon tank (Babs - I live in Central MA, and the total price thru National Grid is around $0.13/kWh incl. delivery charges). Here's my question... when I eventually go solar, can I retrofit any electric tank to fit my solar system?
  16. Nofossil

    Nofossil Moderator Emeritus

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    IMHO, the answer is yes. I would use solar to heat a larger tank that can preheat the water going into the existing electric tank. I have another thread that documents what I did for solar hot water. In my case, the domestic hot water tank was an indirect oil fired unit, but the principle is the same.
  17. cbrodsky

    cbrodsky Member

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    You can but you won't get as good performance with your solar setup later.

    If you're going that way, you might be better off simply buying a solar storage tank up front that includes an electric element. It's basically a somewhat more expensive highly insulated water heater that includes all the ports you'll need for connection to any type of solar HW system along with a good in-tank heat exchanger that will help optimize your stratification, which is an important part of how well a solar HW system will function. The solar tanks are usually 80 or 120 gallons. You can find them online too.

    -Colin
  18. thephotohound

    thephotohound New Member

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    That will probably make even more sense a few more years down the road, as I plan to heat 1000 SF of new construction (all bedrooms) strictly with solar. Is heating this size space just a pipe dream, or possible (for a reasonable price)?
  19. Nofossil

    Nofossil Moderator Emeritus

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    Others may have more concrete data, but my observation is that the sun doesn't always shine in New England. I think the 'strictly' part is a pipe dream, but you could certainly reduce the need for other forms of heat. Some sort of storage would be necessary. Our house heats itself via passive solar just fine during the day, but we have to supplementary heat during the night. Remember that nights are longer than days this time of year :)
  20. cbrodsky

    cbrodsky Member

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    I think at best, you could supplement your heating needs a little bit but you'd need a very good site for sun exposure with the panels mounted at just the right angles, and would need to plan on radiant heat that runs in the 90s. Baseboard requires temperatures much higher than what you'll get out of solar in the winter.

    In the summer, you'd be so incredibly oversized that you'd have to build yourself one awesome outdoor spa to keep them cool :)

    The price will also depend greatly on what tax incentives are available, but in general, I don't think you'd find it to be cost effective compared to other options.

    -Colin
  21. babalu87

    babalu87 New Member

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    A water softener is probably a MUST for a tank HW system.
    My well water is hard as a rock and full of minerals but the water softener makes it nicey nice.

    If too much heat during the summer is an issue with a solar system couldnt one just cover up a portion of it during that time of the year?
  22. cbrodsky

    cbrodsky Member

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    That's true if you don't have a true solar HW tank/exchanger system and is an important point to be aware of - it is one of the reasons why the retrofit solar wands that you just stick in the top of your existing tank can't deliver the same results. You do best by selectively pulling out your coldest water to send it up to the solar panels, and then sending that water back such that it ends up in the hotter portion of your water storage.

    However, the Rheem tanks achieve phenomenal temperature stratification within a single (large) tank - regularly maintaining 40-50 degree differences top-to-bottom. There is a diptube that reaches to the bottom of the tank to draw water for heating and a second shorter diptube that returns it to the top of the tank. It does this with remarkably little mixing as well, as evidenced by the very large temperature difference you can observe at any given time in the tank. I'm not sure if they have internal baffles that are somehow assisting this process or not.

    -Colin
  23. babalu87

    babalu87 New Member

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    Update
    After looking through the old oil receipts I find out that we have been burning about 200 gallons of oil per year to heat hot water.
    Even at $3.00 a gallon that is probably cheaper than propane or electric.

    I am starting to think that a Boilermate and the eventual Solar attached to what we currently have may be the best option.

    Since my sister is in the propane and propane accessories business I know a propane system for a family of four is going to go through 25-30 gallons/month in "Winter" and 15-20/month in the "Summer".

    Wish I knew what an electric hot water tank really used per month.
  24. Nofossil

    Nofossil Moderator Emeritus

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    I don't know, but that's never stopped me ;-)

    First of all, the 15-20 gallon per month number rings true and is very consistent with everything I've seen. Oil is about 130k BTU per gallon. An indirect tank gets heat transferred to it with something like 75% overall efficiency, so at 20 gallons per month you're putting about 2 million BTU into the tank each month. Converting BTU to KWH, that would be somewhere in the 500 to 600 kWh range. (Electric hot water heaters are 100% efficient at turning electricity into heat in the tank)

    On-demand heaters are more efficient because they lose less heat to the environment when no hot water is being used.
  25. Eric Johnson

    Eric Johnson Mod Emeritus

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    I put in an electric water heater for summer duty, and I know my electric bills didn't go up by $50 a month. And my girls use some hot water. But it should be an easy calculation to make, given the right information. One way is to look at what it says on the side of the water heater, i.e., "average annual cost of this unit," and so forth.

    It pays to remember that an electric water heater is 100 percent efficient, at least as far as energy input is concerned. Nothing goes up the stack and nothing is lost moving water between appliances. No pilot lights, etc., either. That doesn't necessarily make electric a better deal, but it's something to consider. The thing I like about electricity is that the rates are set by the PUC--so they're not going up without a lot of advance notice and a lot of public scrutiny and input. Can't say that about oil or gas, I don't think.

    Somewhat OT, I just passed by the local gas station and was shocked to see diesel going for $3.65 a gallon. If that's the trend, the heating oil probably isn't far behind. Not to be a total Liberal, but you'd think the govt. would think about capping the price of home heating oil at some point or people won't have any money left over to pay their taxes come April.

    EDIT: Nofo beats me to again. He made my point about efficiency and gave you some numbers to work with. Good man, as usual.
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