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

  1. #1
    DIY Senior Member jch's Avatar
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    Question Recommended replacement for ancient oil-fired boiler ? Gas boiler? Heat pump?

    We have an old oil-fired boiler (1970's?) that is so expensive to run that we've been using portable electric heaters in its place (yet still saving $1,000+ / year in the cost differential).

    **Looking to get a permanent solution in place and am not sure where to start. Do I install a gas boiler? Condensing? Modulated? or a multi-stage Heat Pump?

    Location: Victoria, BC
    Blower-door test: 6.39 ACH
    Average HDD/yr: 1066
    Design temperature: -10C (14F)

    Original 2x4 stucco framed house was was built in 1942, with 900 sq ft heated by an oil-fired boiler and cast-iron radiators (running around 180F). Uninsulated concrete basement walls, not directly heated, but used for office space. Main floor walls insulated 2 years ago with dense-pack cellulose.

    A 180 sq ft addition was added on plus the 500 sq ft attic was developed about 20 years ago. Both areas have electric baseboards.

    When the oil-fired boiler was in operation, a tech measured its efficiency at 69% based on flu-gas temperature. Its placard says 78,000 btu/hr.

    Our current fuel costs are:
    Oil: $1.36/Litre ($0.0356/MJ)
    Gas: $0.0143/MJ
    Electricity: $0.1034/kWh ($0.0287/MJ) - but will be increasing 20% over the next 2 years.

    Based on the actual oil usage before we stopped using it, and on the jump in electricity usage after we became all-electric, the amount of Delivered heating capacity works out to 22,000 btu/h (6.4kW) including 40% oversizing.

    What would you folks recommend??
    ----------
    - John

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Look into a mini-split heating/air-conditioning unit. Your heat load is reasonable, your low temp expectation is well within their capabilities without auxiliary resistance heating. It does depends somewhat on the room layout and how open the arrangement is. They can come with multiple heads. While you may not need a/c often, it'll be there should you want it. At your implied heat load, the smallest boiler available would still be big, and big on a boiler means less than optimum performance. You can make it work reliably if you get someone that is good, but many of the hacks out there will not give you a good end result.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member jch's Avatar
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    Interesting suggestion. Am I correct in assuming that mini-split heads are similar in noise to those heating/cooling units found in many hotels? If so, I don't think I could take the noise. One thing I really like about electric baseboard / hot water heating is that it's essentially silent.

    Or are they quite different from the hotel units?
    ----------
    - John

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    Retired Defense Industry Engineer jadnashua's Avatar
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    VERY different. The compressor is outside, only the circulator fan and evaporator coil is inside. Many have variable speed fans, and are almost silent on low, where they'd be most of the time unless it was a really cold day. The fan is typically mounted high up on the wall. There are some that can feed a duct system, but you probably don't want to add ducts. You've probably come across some, but didn't know it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member jch's Avatar
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    Sounds like it might be an option for replacing the resistive baseboards too...

    Am I correct in assuming that, like window air conditioners, we'd need a head inside each room? It a 40's house -- the opposite of an open concept.

    If so, how do you run the refrigerant to the front rooms of your house without tearing the walls apart??
    ----------
    - John

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    Retired Defense Industry Engineer jadnashua's Avatar
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    It all depends on whether you close off the doors regularly or not how many heads you need. Some units can support a fair number. Some also support feeding ducts which would allow it to serve multiple rooms. SOme of them come with precharged, quick connect tubing, sort of like the hose on an air compressor. You'd need to talk to someone that deals with them. There are some other threads that discuss them a fair amount here, try the search function and read up, then come back with some more questions. Bottom line, though, at least for capability, where you live, it should be more than adequate to heat and cool the home.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    Ductless air source heat pumps are VERY quiet compared to the PTHPs found in most hotels, and are nearly 2x as efficient. While running with the blower in low-speed mode (which is where they will be most of the time if correctly sized) they're quieter than most refrigerators. At high speed it'll be comparable to or a bit louder than a refrigerator, but that's about it. There are now MANY home's on the other side of the Strait from you (including some of my relatives) heated with this technology, and in your climate the average efficiency is comparable to ground source heat pumps (but a fraction of the cost.)

    With a heat load of 22KBTU/hr and a 99% outside design temp of about -3C (yes, I know it gets colder than that in Victoria, but -10C is about a 99.5% design temp, and overkill) you'd be able to do pretty well with a single 1.5 ton mini-split, or a pair of 3/4 ton units, which would run ~$4500-5000USD installed, if you lived in Port Angeles or Port Townsend- I'm not sure how competitive it is on Vancouver Island. On the US side there has been a large scale promotion & study of this technology over the past half-decade or so with well documented efficiency & cost averages.

    A room-by-room heat load calculation is in order- you don't need one mini-split head per room, and if you oversize the head for the load it'll cycle on/off rather than modulate with load, which cuts into both efficiency and comfort.

    Mitsubishi & Fujistu own the lions share of the North American market, and having multiple installer resources near you can be more important than the absolute raw efficiency numbers. That said, the popular Fujitsu AOU-xxRLS2 series edges out the popular Mitsubishi MXZ FExxNA in side by side third party lab testing. A pair of FE09NA or 9RLS2 is probably your best bet, one head per larger zone, using the existing electric baseboard for temperature balancing on the doored-off rooms. If yours is a fairly open floor plan a single FE18NA or 18RLS2 would get you there. (That works just fine for my relatives on Whidbey Island and Port Orchard, both with heat loads comparable to yours. Both went for -FE18s rather than -18RLS2s due to the much higher density of Mitsubishi installer expertise in their local areas.) Since your calculated heat load includes a 40% oversizing factor, you may be able to do it with a single 1-ton rather than a 1.5 ton, which put out 15,000BTU/hr at -15C, and a good bit more at -3C. (22,000/1.4 = 15,714 BTU/hr.)

    There are mini-duct cassettes that can sometimes work with pre-existing duct work, but they're both more expensive and measureable less efficient unless your ducts are very short, very tight, and properly sized. You may have to go with a 2-ton to get the capacity with that approach unless the ducts are pretty ideal, and you'll likely run a true coefficient of performance of about 2.5-2.8 compared to 3-3.5 using ducless heads. That's still more than twice as efficient than with baseboards, and not a bad option if your floor plan isn't very open. Mini-duct cassettes can be used to split the output between adjacent rooms with very short duct runs at comparable efficiency to the wall-unit heads though, and is sometimes a better solution than multiple oversized heads or baseboard heaters.

    [edited to add]

    If you opt for a gas-fired solution, your heat loads are well within the bounds of a condensing tank type water heater like the Vertex, and now that you've insulated the place you don't need anything CLOSE to 180F water. In many systems with high-mass radiators in houses that were originally uninsulated, leak air, and fenestrated with single-pane windows (no storm windows) the output of the radiators is sufficient to handle the design-condition load with 125-140F water after the insulation & window upgrades. Replacing the electric baseboards with euro-style panel radiators or recycled cast-iron baseboard is usually a big uptick in comfort too.

    But at your fuel & electricity pricing ductless heat pumps will be substantially cheaper to run, even if electricity goes north of 15 cents/kwh. A condensing HW heater based system may hit 90-92% average efficiency if done reasonably, but the ductless will run better than 300% efficiency in your climate. Do the simple math on your source-fuel $/MJ using the efficiency corrections, and you'll see it's a no-brainer, if the financial aspects dominate your decisions.

    If the externalities matter more than the economics, the ductless solutions still win (big time!), since the local grid in BC is very low-carbon/low-pollution, and even clean-burning gas has a much higher carbon footprint.
    Last edited by Dana; 07-12-2013 at 11:41 AM.

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    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    Dana has it. Vertex or Polaris with a sub-system to isolate potable from heating fluid and pump both sides with weather sensitive controls for more quiet comfort than most realize or can afford for that matter. Here in Minnesota we think of the long cold winters first and the short hot summers second.

  9. #9
    In the trades Dana's Avatar
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    In Victoria it's more like long very mild winters, with short tepid summers that feel kind of like May in Minnesota, before the heat & humidity arrive.

    Mark Twain has been credited with the statement:

    "The pleasantest winter I ever spent was one summer on Puget Sound."

    Which could well have applied to nearby Victoria, which has ever so slighly warmer waters than Puget Sound to moderate the winter averages, but is similarly mild & comfortable most of the summer. The 99% / 1% outside design temps are 26F / 80F for Seattle, 26F / 75F for Victoria, with very low (negative, actually) latent loads for both. July in Victoria makes for a pretty pleasant winter month indeed! :-)

    Even though the heating season is fairly shallow by midwestern terms, (there hasn't been a year since 1957 that logged more than 1000 HDD base 65F in any single month in Seattle) it's long- about 10, sometimes 11 months out of the year, assuming any month with more than 100 HDD and at least 2x more HDD than CDD counts as a heating season month. Most people are still running the heating in June, and back up again in September, sometimes sooner. Most years won't see ANY single month with as many as 100 CDD, maybe one out of every five years, looking at 50-year datasets.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Depends on if you want some dehumidification or not. The mini-split would provide that. Course, you can get a stand-alone unit to provide that, should you wish. But having the mini-split would allow that as a side benefit for your heating demand.

    Cost wise, the Polaris is likely your least expensive option, but is less flexible.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    Dew points in Victoria almost never exceed 60F, and when they do it's a short-lived event. Latent-cooling/dehumidification is a moot point there- averagel latent loads are actually NEGATIVE. (It sometimes makes front page news in Seattle when dew points break into the mid-60s, which would seem pretty comfortable compared to what we have going in New England this week, eh? :-) ) Most of the summer dew points stay in the 50s. So far this year the outdoor dew point has yet to break 60F in Victoria, though it nudged up close a few times the week of 30 June 2013 (pull up a dew point graph, and take a gander at the dew point history.)

    Cost wise a Polaris based hydronic system will come in considerably more than a couple of 3/4 ton mini-splits and an electric cove-heater or three for temperature balancing, especially if you add panel radiators or something better than fin-tube for the attic & addition zones. (I've penciled that out more than once for relatives in the region.)

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    DIY Senior Member jch's Avatar
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    Thanks for all the great information so far!

    I've had a few contractors come in to talk about:
    - multi-stage (hydronic) heat pump replacements for the oil-fired boiler: nobody here offers them;
    - mini-split heat pumps (Lennox and Fujitsu): great efficiency numbers (although $6k + 3k for each additional head);
    - gas forced-air (requiring 5-6" air ducts to be installed throughout the house, including boxed-in runs up to the 2nd floor);
    - gas boilers (Lochinvar, Weil-Mclean)

    Only one of the contractors said they do an actual heat-loss calculation for sizing. The others either measured the size of the existing radiators, used the square footage, or looked at the nameplate on the old boiler to make their sizing recommendation.

    So I'm going to go with the heat-loss calculator folks if possible, but use the other estimates as a sanity check.

    I really like the idea of a heat pump, but all our rooms are small (~100 sq ft) and we usually have the doors closed (for sound). The smallest head they had was 7,000 btu/h which would make it smoking hot (or cycle a lot) and the ducted version would have to sit in our (super-hot/cold) side attics which would negate a lot of the efficiency. They'd also be running their 3" piping up the outside of our walls which would definitely scream "retrofit".

    So, for now it's looking like a gas boiler. Thanks for all your help so far. I'm sure I'll have more questions as things progress.
    ----------
    - John

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    In the trades Dana's Avatar
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    While measuring the radiation is necessary for a system design, it's useless for sizing the boiler. Using the nameplate output of the older boiler is even worse, since it's a meaningless bit of data even for designing the system. Only the contractor who does heat load calcs is worth considering.

    The mini-split folks sound WAY overpriced. In WA the cost adder per head for multi-splits is about $1500, not $3K.

    For $3K you can even install a standalone 3/4 ton mini-split and still have money in your pocket! (Maybe you need some cheap undocumented immigrants from across the strait to come install 'em? ;-) ) The most expensive quote I ever saw for a 1-ton Fujitsu was about $4.5K, which was insane compared to what competing bids were for the same job- slightly more than the 1.5 ton Mitsubishi unit that was eventually installed there. A 3-head 2-ton multisplit might come in around $7.5K ($3K for the compressor unit, $1.5K per head) for the whole thing, not $6K + $3K per head. The hardware itself just isn't that expensive, maybe $3500, and installation of a 3-fer is about 1 man-day, 2 at most. At a burdened cost of $100/hr for the installers even if it's a 2-day (16 hour) install that leaves a reasonable gross margin for the contractor.

    If you're allowed to do your own electrical work without a license in B.C., a dedicated DIYer can usually handle the bulk of a ductless installation if they're reasonably competent, and only call in the pros for the final refrigerant-charging/commissioning & test to keep the warranty fully up to snuff, probably for less than $500 of tech-time. Sizing the heads for the intended spaces and deciding on the number of heads takes bit of head scratching and crayon-on-napkin math.

    The gas boiler approach surely works, and should be cheap enough to run. Just be sure to go with the absolute smallest in the series, and be sure the radiation on the smallest zones are sized to deliver 100% of the minimum-fire output of the boiler at 50C or less.

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    DIY Senior Member jch's Avatar
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    I was shocked at the estimate for the Fujitsu mini-split too. He wanted to put in an AOU36RLXFZ plus two ASU12RLF's and one ducted ARU12RLF. This would not be EnergyStar rated and would cost $10-11k with installation. One head would be in the 12x12' living room and so would probably be cycling like crazy.

    He also said he could do an AOU24RLXFZ (2-ton) with an ASU7RLF, an ASU7RLF and an ARU9RLF for $9k-ish.

    But I was really hesitant about his (lack of) determining the actual heat loads.


    As far as installing my own 3/4 ton mini-split in the coldest part of the house, I'd still need something to take care of the rest of the house. Plug in 110V baseboards have worn out their welcome...


    One thing I was toying with was zoning a gas boiler with one zone for each bedroom so we could use a setback thermostat in each room and make it easier to give everyone the temp they like and not run in to the heat balance issues we had when the oil boiler was in operation. This would allow us to move the *entire* house (basement + 2 floors) to *one* heating system, with the option of temporarily turning off the heat to unused rooms (I have a home office).

    Currently the bedrooms require <500W during regular heating season (~1,500 btu/h) so I'm not sure whether this would work if only one zone were calling for heat. I did a Manual-J on the coldest area and came up with 5,800 btu/h which is still fairly low.

    The smallest boilers offered (by a different contractor) are:
    Lochinvar WHN055 (55,000 btu/h, 96%, 5-to-1 turndown with outside reset)
    Lochinvar CDN040 CADET (40,000 btu/h, 95%, 5-to-1 turndown with outside reset).

    Both have stainless boilers, but only go down to 8,500 or 11,000 btu/h without cycling... i.e. bigger than any one of the zones would need.

    Suggestions?
    ----------
    - John

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    In the Trades Tom Sawyer's Avatar
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    I'm not convinced a mini split is the way for you to go. I like the Locnnivar boilers and you could look into these http://www.qhtinc.com/radiators/. Along with thermostatic radiator valves to control heat to each zone or individual radiator. The key here is an accurate room by room heat loss and sizing the radiators properly so that the boiler will actually condense.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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