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Switching from oil fired hydronic heat with cast iron radiators to gas fired forced air w/AC

hutchinsronhutchinsron Posts: 8Member
Hi Everyone,
This is my first post here. I live in a 150-year-old house with about 2800 square feet (less actual living space). My wife and I have been evaluating our heating costs and at the same time are looking to install central AC. We are leaning towards moving to a gas-fired (natural gas is already in the house) furnace and using a forced air system with both natural gas in the attic and basement (no closets to send duct work down/up). This is obviously a big investment so I am looking to get opinions. I hear how this will save us money in heating costs, but the oil people always talk about the warm of cast iron radiators. Our current boiler was made in 2002 and recently we were told we needed to put 1400 into it for a new larger expansion tank and new coil (on demand hot water built into boiler). Looking for insights.

Comments

  • SnowmeltSnowmelt Posts: 1,101Member
    Keep the boiler, get a separate ac system, give us some pics of boiler
  • hutchinsronhutchinsron Posts: 8Member
    edited January 17


    Here is one photo of the boiler's info plate. I will work on getting a picture of the unit itself which is a Peerless. I believe 286,000 BTU output but will get more info on the boiler and a better picture later. Single zone if that helps.
  • KC_JonesKC_Jones Posts: 4,182Member
    Do you have steam or hot water system now?

    I'd keep the hydronics, run it on gas and then add AC, no way would I let anyone tear out the radiators. Your comfort will suffer.



    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    https://www.facebook.com/media/set/?set=a.10202744301871904.1073741828.1330391881&type=1&l=c34ad6ee78
  • BrewbeerBrewbeer Posts: 592Member
    Depending on where you live, and how often AC is required vs. how often heat is required, I will second snowmelt's recommendation to install a completely separate AC system.

    I would keep hot water heating, install an indirect water heater, and abandon the tankless coil. The only problem with this approach is that your boiler is probably 3-4 times bigger than needed for your space heat requirements.

    Interestingly, I did the exact opposite of what you are thinking about doing: I ripped out a forced air heating system (w/ AC) and replaced it with a hot water system, due to the superior comfort offered by hot water heating.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • KC_JonesKC_Jones Posts: 4,182Member
    Oh yeah, that boiler is most likely triple the size you need and costing you money.

    No matter what you do, if you get any new equipment the contractor MUST do a room by room heat loss calculation to size the equipment properly.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    https://www.facebook.com/media/set/?set=a.10202744301871904.1073741828.1330391881&type=1&l=c34ad6ee78
  • Jamie HallJamie Hall Posts: 11,162Member
    You will be much better served -- and save considerable money -- and have more comfort -- if you update the boiler with a modern mod/con (modulating/condensing) boiler sized to fit the heating needs of your house. You can do this at your leisure, when and if the old boiler needs serious work. An accessory like the new expansion tank will not be lost investment, if it's sized correctly to the system, as it will be used for the new one as well.

    If you are presently satisfied with your hot water from the boiler, you can keep that. However, you could also install a new, gas fired hot water heater as a stand alone unit, if you liked and preferred to do that rather than have the coil in the boiler replaced.

    On the A/C, you have, really, two choices, either of which are reasonable. One would be to install two A/C units, as you suggest. The one in the attic I would be a little concerned about; is the attic insulated and a partly conditioned space? The other option would be to consider two heat pumps, which can function either as air conditioning in the warmer months, or as heating in the cooler months -- the "shoulder" seasons. The existing hydronic system in the latter case, would be used for when it gets colder.
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • hutchinsronhutchinsron Posts: 8Member
    KC_Jones said:

    Do you have steam or hot water system now?

    I'd keep the hydronics, run it on gas and then add AC, no way would I let anyone tear out the radiators. Your comfort will suffer.



    Hot water.
  • hutchinsronhutchinsron Posts: 8Member
    edited January 17
    Thanks for the input so far. Here is the answer to a few of your questions. The attic is insulated up to the knee walls but the roof is not (floor has sheathing and under that is blown in rockwool insulation), I am looking to insulate that now regardless if we decide to go further with a new system. I am trying to figure out how to handle the knee walls being sealed up as I would think I would have to get my proper vent to link into the soffit vents in order to keep the roof cold to prevent ice dams.
    We are located in Connecticut so zone 1 I believe.
    We don't mind the hydronic heat, its the cost of oil that bothers us. We know we can do some things to help manage our costs such as the indirect HW heater which people have already suggested.
    I am encouraged to hear people say stick with the hydronic heat and just do a separate AC system. We originally got into this because our natural gas supplier was offering some rebates and financing options by moving to gas heat. I have been told by one plumber already he wouldn't suggest converting our present boiler to gas because the efficiency wouldn't be there and you are talking about then relining the Chimney at a cost of about $.
  • hutchinsronhutchinsron Posts: 8Member
    Yes, hot water system 1 zone. A few cool rooms that are on the end of the line.
  • pecmsgpecmsg Posts: 903Member
    Do not give up the HW.
    Search drafts and forced systems. Unless sized and installed perfectly (not going to happen) there will be cool / cold air drifting down.
  • KC_JonesKC_Jones Posts: 4,182Member
    I wouldn't convert that boiler because it is over sized, think clown car level of ridiculousness for the amount of over sized it is.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    https://www.facebook.com/media/set/?set=a.10202744301871904.1073741828.1330391881&type=1&l=c34ad6ee78
  • Jamie HallJamie Hall Posts: 11,162Member
    Some years natural gas is cheaper. Some years it isn't. I do think, though, that in the long run you will be best served with a modern mod/con boiler - which means gas, among other things -- with all the bells and whistles.
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • GWGW Posts: 3,445Member
    edited January 18
    2.5 gallons of oil is 350,000 btu input. That’s enough for you and a few of your neighbors.

    You’re on a pro- hydronics web site, I would rather see you get a new properly installed boiler and get a couple of ductless units.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    www.wilsonph.com
    [email protected]
  • HVACNUTHVACNUT Posts: 2,548Member
    > @hutchinsron said:
    > I have been told by one plumber already he wouldn't suggest converting our present boiler to gas because the efficiency wouldn't be there and you are talking about then relining the Chimney at a cost of about $.

    He must be in real real rural Connecticut.
    He's referring to an atmospheric gas boiler and installing a stainless chimney liner.
    Read what @Jamie Hall wrote and run with it.
    And dont even let that plumber tell you the time because he still uses a sun dial.
  • flat_twinflat_twin Posts: 224Member
    I was in your shoes a couple years ago. 1780 sq ft two story built in 1835. We kept our cast iron radiators, abandoned a chimney that would have required some repair and a liner, installed a natural gas modcon boiler and a year later replaced an old electric water heater with an indirect water heater tied to the boiler. Best heating system we've ever had and cost 45% less to run than the fuel oil boiler it replaced. We use two window air conditioner units, one upstairs, one down. I can see replacing those eventually with a pair of mini splits which would also give us some back up for heating if there was ever a problem with the boiler.
    As suggested, you need to know your home's heat loss and you need to know the EDR or output capabilities of your cast iron radiators. Then you'll know if you're able to take full advantage of the efficiency of the modcon boiler. Keep those radiators!
  • HVACNUTHVACNUT Posts: 2,548Member
    As far as the A/C, or heatpump goes, are there closets or inside corners that can be boxed out to bring duct drops to the first floor? Maybe you can go with one system fed from the attic.
  • hutchinsronhutchinsron Posts: 8Member
    HVACNUT said:

    As far as the A/C, or heatpump goes, are there closets or inside corners that can be boxed out to bring duct drops to the first floor? Maybe you can go with one system fed from the attic.

    Yes, one of our issues related to AC and needing two air handlers is because one side of the house has no closets and we don't want to box any ductwork in, especially since our rooms are ringed with beautiful plaster crown and cove moldings.

    So a few people have brought up replacing the currently oversized boiler with a more accurately sized modulating/condensing unit. From what I have ready our cast iron radiators need water temps close to 180 and that's something that doesn't really work with these modulating condensing boilers because they are not efficient and those temps, therefore, negating the advantage.
  • BrewbeerBrewbeer Posts: 592Member
    Post some photos of your radiators. Unless they are really small, they don't need 180F water temps.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • Jon_blaneyJon_blaney Posts: 55Member
    I went through this same process recently. The cost of all new equipment will cost you a goodly sum. You have the advantage of having natural gas, which I did not. I kept my current hot air furnace and put in window ac units. The new units are much more attractive than old style ones, weigh much less, and cost hundreds not thousands. Just do a careful install. You also do not have to look at them all the time. I would look at a stand alone hot water heater so you can turn the boiler off in the warm weather. Maybe a indirect tank and a stand alone in series.
  • rosbournerosbourne Posts: 7Member
    Hi,
    I am running an oil system with steam and I am being told to switch to gas. The boiler seems relatively new got with house in 2010, house was made in 1930.

    I have attached a few pictures of boiler and also the piping which a plumber said he thought was piped incorrectly. I notice the radiators to the left side seems to get way more heat than radiators on the right also, based on the loops in the pipes from my layman eyes piping seems inefficient. I have been playing around with gorman valves to try and balance the system(Thanks to this forum)

    I have no intention of selling this house anytime soon.
    I have gas in property for water heater and stove.
    (I am located in Bronx, NY)
    I don't think my oil bill is super high compared to other folks I know but my buddies using gas claim their bills are way lower.

    So my question is should I switch burner to gas or replace the entire unit and do over pipes etc?. I see lots of mention about mod con.
    TIA
    Robert
  • Jamie HallJamie Hall Posts: 11,162Member
    @rosbourne -- you'll get much better results here if you start a new thread...

    @hutchinsron -- it is quite true that the big radiators will need 180 F water to put out their maximum output, and at that you won't get condensing -- nor, if the boiler is sized right, will you get any modulation. However -- they don't need that temperature if it is warmer outside than the design day, and by definition the design day is extreme. With a properly calibrated outdoor reset curve for the boiler, it is quite likely that most of the time they will be operating at a much lower temperature, and you will get both modulation and condensing -- and the related higher efficiency.
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • rosbournerosbourne Posts: 7Member
    Thanks Jamie, did as u suggested
  • SeanBeansSeanBeans Posts: 403Member
    Turns out those radiators willl be getting 212+ degree @Brewbeer
  • BrewbeerBrewbeer Posts: 592Member
    @SeanBeans why is that? OP indicates they have a hot water system.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • SeanBeansSeanBeans Posts: 403Member
    edited January 18
    He posted a photo of what looks to be a steam boiler. @Brewbeer

    In which case you can throw that idea of getting a mod/con out the window! @rosbourne

    On second glance, I 100% thought rosbourne was the OP..

    Oops
  • HVACNUTHVACNUT Posts: 2,548Member
    The larger the radiators and water content only gives you another reason to go with a mod con. I think you wrote "from what I've read..." typo in there. Read again. You misinterpreted the benefits of large piping and emmiters with a mod con.
    With outdoor reset the boiler will only get to 180° on the coldest day(s) of the year. The curve to be set by the installer. Ex. 180° boiler temp @ 0° outdoor temp
    163° boiler temp @ 23° outdoor temp.
    All while keeping the temperature in your home steady.
    But then again, I'm biased towards oil so never mind.
  • hutchinsronhutchinsron Posts: 8Member
    Hot water system. 1/2 copper feeds from loop to the CI radiators. House is assumed not to have insulation in the walls, wood windows about 50+ years old. Wood siding with vinyl siding over that.
    I think those details should give you the more complete picture. I will work on getting a few picks up of the CI radiators and boiler. I really appreciated everyone's insight.
  • flat_twinflat_twin Posts: 224Member
    edited January 18
    Hot water cast iron rads max output is calculated with 180 degree water. They do not require 180 degree water. There are charts to show their output at various temperatures. It is extremely likely your house's heat loss is far less than it used to be with improvements like better door seals, windows, insulation in the attic and walls.

    This is exactly what happened to our house. My radiators all combined are rated for 101k btu output at 180 degree boiler water. With the improvements mentioned above, my heat loss is now only 57k btu. This means on the coldest day of the winter the boiler only needs to make 126 degree water. On warmer days the boiler water may only be 100 degrees or 90 degrees. Better still, it means the entire heating season my modcon boiler is condensing and achieving 95% efficiency.

    That's why you have a huge advantage just having those cast iron rads in your house. Modcon boilers are a perfect match for all that mass.


    Find your radiator type and size on these charts. You can calculate the max output of your radiator system.

    https://www.expressradiant.ca/pdfs/product_classic_sizing_how_to.pdf
  • GWGW Posts: 3,445Member
    confusion galore-- we are talking hot water it seems.

    So big cast iron (CI) rads are super good. No need to get to 180 in many cases. As the heat dudes know, lower boiler temp is better, and the bigger the better for the CI rads. The bigger the rad, the lower the boiler temp that's needed to heat the house.

    If the rads are jumbo- may need to upside the boiler a smidgen to handle all the mass. I had a sales guy years ago- I went to install the new mod con with my crew and almost gasped out loud when I saw the large CI system (big diameter steel and large rads). We installed the dinky mod con and I just crossed my fingers. Never got a call but that was just too close. "Don't turn the thermostat up and down" was our instruction to the homeowner.

    Look at the Viessmann CU3A, it's a horse and doesn't need all the protection items the wall hungs or the aluminum boilers do.


    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    www.wilsonph.com
    [email protected]
  • mikeg2015mikeg2015 Posts: 987Member
    Get small furnaces... small as possible to satisfy AC airflow needs and keep the oil boiler for the really cold weather. Run the furnaces and eventually change the burner on the oil boiler or replace it.

    You will get zoned heating in mild weather when you need it. And get nice warm radiant in the coldest weather for comfort. Plus, furnaces are a second backup heat source.

    I wish I had done that. Equipment cost of a single stage furnace is not a lot more than an air handker if you keep it small.

    If you need a 2 ton AC put in a 40-50k furnace. If you need a 3 ton put in a 60-70k furnace.

    At night, you can run just the upstairs furnace only for example.
  • hutchinsronhutchinsron Posts: 8Member
    I realize I never posted pics of my boiler or radiators for the person that was asking. These are the commonly sized radiators I have, large ones. Thanks again for everyone weighing in. Despite the HVAC guy I had come in to give me a quote and was trying to talk me into gas-fired furnace with hot air/AC combination I have yet to see a proposal from him.







  • SteamheadSteamhead Posts: 13,281Member
    You could have that boiler converted to gas, using a Carlin EZ-Gas burner.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
    https://heatinghelp.com/find-a-contractor/detail/all-steamed-up-inc
  • IronmanIronman Posts: 5,221Member
    A properly sized and installed mod/con and indirect could very easily save you 30 - 40% in energy cost. We do it regularly with old systems and our customers confirm it to us.

    The key is to find a COMPETENT hydronic contract and that's not always easy. Check the contractor locator above or post your locale.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
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