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30 year old oil boiler conversion to mod con propane

Ok so I'm a novice when it comes to this stuff but I'm looking for guidance from all of the knowledgeable people on here.
I live in southern New Hampshire. My house is over 30 years old. The current oil boiler was installed when the house was built. The boiler has been "rebuilt" I have been told at least once. I know one of these days it's probably going to leave me stranded and that's what I want to avoid. I'm wondering first off if it would be wise to switch to propane that is already on my property with its higher efficiency. I have heard both good and bad thing about the new gas mod con boilers and don't know exactly what true and what's sales pitches from the local heating guys. I currently have a an indirect hot water heater also that I have been told is the best way to maintain my domestic hot water supply. Problem I have with the super store is I run out of hot water with one shower. It takes 15-20 min to replenish the full 40 gallons after the shower has been completed. I can't even fill a bath tub to an adult level with my current set up. I'm wondering if my current oil boiler is undersized or just plain set up wrong. I would like to switch to a new LP mod con and possibly get rid of the 40 gallons of hot water I'm keeping warm all day and night. Also I'm seeking to reduce my heating cost as well due to my 2400 sq ft house costing me $3400 to keep at 67* for5 months. If anyone could help it would be greatly appreciated.

Comments

  • Paul48
    Paul48 Member Posts: 4,469
    You're planning for next spring?
  • njtommy
    njtommy Member Posts: 1,105
    edited November 2015
    Well a nice mod boiler would be a nice set up with some either extra storage capacity for DHW, but it may not be your best option.

    What temperature is your tank storing water at?

    You may need just plain more storage.

    A big factor on filling that tub is the amount of water flow you need to fill it and what temperature your trying to achieve.

    How many gallons is the tub?

    Also if your thinking mod con boiler that is a combi unit you will end up sizing the unit too big for the heating load just to handle your needs of DHW.

    If you stay oil I would only install a 3 pass oil boiler with outdoor reset control. Along with a larger indirect tank set at around 150 degrees. Then just mix down ur temp to either 115-120.
  • Robert_25
    Robert_25 Member Posts: 527
    The controls may not be setup properly, and/or the indirect water heater may be piped wrong.
  • Gordy
    Gordy Member Posts: 9,546
    edited November 2015
    How about some pics of present setup in boiler room? Several shots of boiler it's piping, and indirect, and it's piping.

    What type of emitters does your home have? Baseboard, radiators etc.

    What is your goal? Get present system working better, or get away from oil fuel with a new system?


    To get high efficiency from a mod/con some things need to fall into place. Proper boiler sizing to the heat loss, and existing radiation survey to see if there is more than enough to allow for lower water temps to get the boiler to,condense.
  • kcopp
    kcopp Member Posts: 4,418
    edited November 2015
    3400 to heat your house is very high for NH. Especially a 30 yr old house. I am in the NH Seacoast , my house is 200+ yrs old, about the same size and I am < 1/2 of that.
    Before going the LP route I would have the house given an energy audit.
    I would also stick w oil unless you are getting a sweetheart of a deal on LP.
    njtommyGordy
  • Chester
    Chester Member Posts: 83
    Get the energy audit. Look into any rebates but well worth the cost in any event.

    The size of the boiler and quality of the installation may be more important than the type of fuel or brand of equipment. Find a contractor via this board or somewhere else that you like and trust and look at pictures of their work. Good heating contractors are real craftsmen and take pride in what they do.

    I have a 30-gallon indirect and have no problem filling a large bathtub. You might start by figuring out where the thermostat on the tank is set. I run mine at 140F and could set it at 160F if I needed to. A higher tank temp would give you more effective shower time because you have more stored energy to draw from. But if you set the tank above 120F make damn sure you have a mixing valve so you don't scald anybody. I'm not sure a 15-minute recovery time is unreasonable, but if your boiler's big enough to heat your house it should give you plenty of Btus for DHW recovery if everything is piped and running correctly.

    How big is your existing boiler? It should have a DOE or I-B-R rating on a label somewhere. This is an educated wild-****-guess but a 2,400 sq/ft house probably doesn't need more than 70,000 to 100,000 Btu/hour. My 70-year-old 1400 sq/ft house has a design day heat load of less than 30,000 Btu/hr. I've replaced windows and done some insulation and air sealing. Even my 57,000 Btu/hr boiler is slightly oversized.

    It would be very uncommon if your existing boiler is undersized. Chances are it's way oversized.

    What kind of emitters to you have? (Baseboard, radiators...?). If you have nice cast iron radiators like I do a modcon is a great fit. If you have baseboards you have to make sure you have plenty of output (linear feet). Baseboards are generally sized to run at 180F, but you need to run lower supply temps with return water temps below 130F or else your modcon will never see its claimed efficiency. You may have to install more baseboard or replace with baseboard that is designed for lower temps.

    If you go with a modcon, what are you planning for intake and exhaust? You can't run the exhaust from a modcon up an unlined chimney and if you line it it has to be according to the boiler manufacturer's specifications, not just the cheaper aluminum or stainless liners most people get. (The beauty of a high efficiency unit is that the exhaust temp is so low but that means the acidic vapor in the exhaust is highly corrosive.) So you need to either put some extra $$ in the budget for that or go through a wall. If you go through a wall put it somewhere you won't mind a gentle cloud of steam when the unit's running. You can drive around and see what other folks' installations look like.

    I've attached a spreadsheet that lets you compare the relative heating cost of propane, natural gas and heating oil. Just plug in whatever numbers are appropriate for you and you can at least get a general sense of whether relatively more expensive propane at a higher efficiency is cheaper to run than relatively less expensive oil at a lower efficiency. But just remember that's only part of the overall equation since you need to look at up-front costs and system performance. "System" includes the house, so get the energy audit!
  • SWEI
    SWEI Member Posts: 7,356
    What are your current prices for LPG and #2?
  • Chester
    Chester Member Posts: 83
    This is a link to a thread from another board that was helpful to me when I made my decision. Among other things it discusses a way to do your own heat load calculation using actual fuel use over a winter period.

    http://terrylove.com/forums/index.php?threads/when-is-it-time-to-replace-the-boiler.60754/