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Thread: Recommended replacement for ancient oil-fired boiler ? Gas boiler? Heat pump?

  1. #16
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    I have designed many combi hydronic heating systems for temperate climates from San Francisco to Anchorage, OK not so temperate. There is but one uncompromising system for moderate sized homes. This is a condensing water heater sized to the heat load and the largest tub, one for output and the other volume. With the addition of a sub-system to separate potable from space heating water and outdoor reset the perfect small footprint is made. We have this system in new homes and old all over N.America. The smallest micro-zone and the largest room are served the same with the efficiency of condensing natural gas.

    I have a heat pump, but it goes off in the fall in deference to the unmatched comfort afforded by our radiant floors. If I didn't have radiant floors, walls or ceilings an old cast iron radiator would be my very next choice.

  2. #17
    DIY Senior Member jch's Avatar
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    Cool--I like the look of the towel bar radiators! Would they be compatible with cast iron rads? Probably running the system at under 120F and need about 150-200W.
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  3. #18
    DIY Senior Member jch's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    The key here is an accurate room by room heat loss and sizing the radiators properly so that the boiler will actually condense.
    There are already cast-iron radiators throughout the original part of the house.

    To avoid changing those, would we just be able to adjust the water temp and water flow rate to get the return temp we need??

    I did a radiator square footage calculation (i.e. sq ft of the radiators themselves) and it appears that we'd get the typical heat output we need if we run the water at under 120F.
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  4. #19
    In the Trades Tom Sawyer's Avatar
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    Perfect, you may want to either individually feed and return each radiator back to manifolds or gang a few up on manifolds. Use 5/8" heat pex and thermostatic radiator valves either at the radiator or on the manifolds will help you balance the system.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  5. #20
    DIY Senior Member jch's Avatar
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    duplicate post removed by author
    Last edited by jch; 07-26-2013 at 10:01 AM. Reason: duplicate post
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  6. #21
    DIY Senior Member jch's Avatar
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    Just had a follow-up call from the mini-split guys...

    1 ton Goodman: $3,700 incl electrical
    3/4 ton Fujitsu: $4,800

    So quite a bit more than the prices you folks are seeing state-side...
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  7. #22
    In the Trades Tom Sawyer's Avatar
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    Oh yes indeed, keep your radiators. Unlike copper fin tube, radiators give you both radiant and convective heat and they will also give you a greater water mass which will allow you to run much lower return and supply temps too.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  8. #23
    In the trades Dana's Avatar
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    Quote Originally Posted by jch View Post
    Just had a follow-up call from the mini-split guys...

    1 ton Goodman: $3,700 incl electrical
    3/4 ton Fujitsu: $4,800

    So quite a bit more than the prices you folks are seeing state-side...
    The odds of any ~1000' house would have a heat load over 20,000BTU/hr @-3C (or even -10C) are pretty remote, provided there is glass in the windows, the doors actually close, and there's at least some insulation. The output of a pretty-good 3/4 ton mini-split @ -15C is typically around 10,000-11,000BTU/hr and considerably higher at -5C. A typical 1-ton puts out ~15,000 BTU/hr @ -10C (which could equal or exceed your actual heat load at -10C). You don't have to take the manufacturers' word for it (but you usually can), many will actually exceed spec on capacity, when bench-tested by third parties.

    For doored off spaces with tiny heat loads, cove heaters (preferably with occupancy sensor cut out, not merely thermostat control) can make up quite a bit on the comfort end when being remote from the fully-heated spaces leads to a temperature sag. The last thing you want to do is put a 6000-9000 BTU head in a room with a design heat load of 1000BTU/hr, but you can reasonably put a 500W (1700 BTU/Hr) cove heater in there, which has huge comfort advantages over electric baseboard, and it'll be able to bring it up to temp at a reasonable rate without feeling like you're in the broiler, and can still be pretty comfortable when the room is still 3-5C below setpoint, since it's heating up the human occupants directly- sort of like sitting in the sunny window on a cold day.

    The average COP of any decent mini-split will be about 3.2-3.5 in your climate, but round down to 3.0 if you're using cove heaters or baseboards for temperature balance. That means your $/MJ cost for heating with electricity get's divided by 3. A condensing boiler or hot water heater will probably average about 95% on the fuel, with another cost adder for the pumping power, but even ignoring the electricity use, multiply your gas $/MJ number by 0.95, then compare the numbers.

    Your per MJ costs from your earlier post:

    Gas: $0.0143/MJ
    Electricity: $0.1034/kWh ($0.0287/MJ) - but will be increasing 20% over the next 2 years.

    Condensing boiler or HW heater @ 95% efficiency: $0.0143/MB x 0.95= $0.0136/MJ


    Ductless & cove heater averaging a COP of 3: $0.0287/3= $0.0097/MJ

    That's 29% cheaper than the condensing gas option, but figuring it which will rise 20% to

    .... (1.2 x $0.0097/MJ=) $0.0115/MJ...

    ...which is still 15% cheaper than heating with condensing gas at todays gas prices.

    Goodman is now owned by Daikin (purchased within the last year). Daikin is the world-leader in variable-refrigerant volume HVAC, and you'd usually be paying a premium per-ton for a Daikin-nameplate mini-split, but it's not clear to me whether what's under the tin on the Goodman will be Daikin vs. somebody else's hardware, but I suspect it's nothing like the Daikin nameplate units. The rated heating output of their 1-ton is only 13,000BTU/hr bit on the low side compared to competitors' 1-tons, and comparable to the -10C output of the 3/4 ton Fujitsu AOU-9RLS2. (Would need the extended range output tables each to know for sure where the Goodman lives) A Daikin 1 ton puts out about 14-15K, a Daikin 3/4 ton puts out about 10K.

    That's not to say that condensing gas won't be a realistic (and quite comfortable) option (and yes it DOES come with hot water heating included) but the installed cost will likely exceed $10K when you include low-temp radiation for what's now handled by electric baseboard, maybe a bit less if you went with a Vertex HW solution (tbd), and it'll cost more to operate. Even at the (truly) exorbitant $4800 quote for the 3/4 ton Fujitsu, a pair of them still under $10K, with enough left cash over for a few 300-700W cove heaters for temperature balancing as-needed.

    But start with the room-by-room heat load, look at the big picture (including the hot water part), and I'm sure you'll figure it out.

  9. #24
    DIY Junior Member American's Avatar
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    I regret removing our old cast iron coal (converted to oil) boiler and replacing it with a new oil fired boiler in 2007. If I had it to do over again, I'd have kept the old boiler and converted it back to coal. Yes, that means two to theree trips to the cellar and a couple of hour work per day to keep the house warm - would it be worth it? Of course all the heating contractors recommended we replace it. I wonder how much additional cash the boiler installer got when he sold our old boiler to the scrap yard. I had no idea how much heavy metal was hiding under the sheet metal box that housed the boiler until I saw him hauling pieces of it up the cellar steps - so heavy he could barely lift them. Alternatively, I'd have gone to gas as there are gas lines in the street here. But at that time, gas and oil cost the same.

  10. #25
    In the trades Dana's Avatar
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    American: Scrap rates for cast iron hadn't peaked yet in 2007, a period where CLEAN shredded scrap STEEL was fetching ~$250-300/ton at the smelter or dock on the way to China (not the local scrap yard.) Even if it weighed a ton (and it might have) don't think for an instant that cast IRON fetched even as much as $50 at the scrap yard in that time frame.



    In 2007 the retail residential price of natural gas in most of New England was still well under that of heating oil. Heating oil hasn't been cheaper than gas on a $/MMBTU basis in this region since back when natural gas prices spiked above the trend lines in 2002.





    In 2007 heating oil was in the $2.50-3/gallon range (~$18-22/MMBTU, source energy) to natural gas peaked at ~$17/MCF (under $17/MMBTU). An 86% gas burner vs. an 86% oil burner would have still tipped in favor of the gas-burner, and a mod-con would have tipped HEAVILY in favor of the gas burner. Even an 82% efficiency gas burner would have had the slimmest edge over 86% oil at the very bottom of 2007 oil prices. The argument might have been made that there was little advantage to making the switch at that time, but it's simply not the case that the cost of oil & gas were truly the same- gas was cheaper, just not all that much cheaper.

    Since 2004 heating with ductless mini-splits has been cheaper than heating with 86% efficiency heating oil in most of New England (and in cheaper local electric utilities it's been longer than that.) At the past 5-year average they are self-financing, paying for themselves in offset oil use in 3 years or less. (Show me a safe & legal investment with that type of after-tax return!) If you are on a gas main and there isn't a huge hook-up fee retrofitting a gas burner to the oil boiler is DEFINITELY cost effective. Otherwise, retrofitting a mini-split would be then next most cost effective strategy. Or, if you don't have air conditioning and are adding it, the upcharge for a heating + cooling mini-split is tiny, and always worth the up-charge as a hedge against gas price increases. During the shoulder seasons when it's 40F+ outside it's cheaper to heat with a mini-split than an 82% efficiency gas boiler due to the extreme efficiency of mini-splits at part load & temperate outdoor temp.

    Even at dirt-cheap $/MMBTU source-energy coal prices, burning coal in a ~50% efficiency antique wouldn't have much economic rationale beyond the avoided first-cost of a new boiler. (And the spectre of carbon monoxide poisoning from using those low efficiency antique boilers wasn't just a bad dream either- it's the reason why people would sleep with the windows open even when it was -10F outside, and needed to put the radiator right under the window to keep from freezing even with the heat on.)

  11. #26
    In the Trades Tom Sawyer's Avatar
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    He probably made about 40 bucks on the scrap which weighed against the stress on his back muscles seems cheap lol

    Your old beast, even converted back to coal would cost you way more to operate than your new boiler. Old boilers had passages large enou to throw a cat through, 800 to 1000 degree stack temperatures were the norm which means that generally, close to 1/2 of the fuels energy was going up the stack. There really is nothing good to say about old boilers except that they sure did last.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  12. #27
    DIY Senior Member jch's Avatar
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    After a long delay, time to get back at it!

    Got a natural gas line installed and ready to go. Heavily leaning towards installing a Lochinvar WHN-055 Mod-Con boiler.

    The problem is that I have an old house, carved up in to little rooms, that people like at different night-time temperatures. My son (who doesn't have a mm of fat on his body) likes it tropical, whereas my daughter likes her room cool.

    Heat loss calcs (@26F/70F) for their rooms are 1,800 btu/h and 1,900 btu/h respectively. Going to use the existing oversized cast iron radiators in their rooms. Calcs show that 120F feed water should put out that much heat.

    Given that the minimum firing rate of this boiler is 10,000 btu/h (and the total house heat loss is 21,100 btu/h), will it be a big problem running individual thermostats to their bedrooms (i.e. each on their own zone) because other zones will likely be calling at the same time?

    Was planning on using a Grundfos Alpha (in AutoAdapt or delta-P mode) driving a 11 port manifold directly (with actuators on each zone). No buffer tank. No primary/secondary loop.

    Am I asking for trouble??
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  13. #28
    In the trades Dana's Avatar
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    As long as all of the radiation is high-mass radiators, not fin-tube, you'll be OK micro-zoning it with a boiler that modulates down to 10K. There may be a few short-cycles over a season when the call for heat is from but one of the smaller zones, but the zone call overlap factor will be high.

  14. #29
    In the Trades Tom Sawyer's Avatar
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    Go with thermostatic valves at the radiators, constant circulation and no room thermostats.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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