Heating small cottage

Discussion in 'HVAC Heating & Cooling' started by Hunter01, Aug 6, 2013.

  1. Hunter01

    Hunter01 New Member

    Messages:
    15
    Location:
    Wisconsin
    I'd appreciate some thoughts: My son lives year-round in a small (660 sq ft) cottage (Southern WI). No crawl space, no attic access, poorly insulated, no natural gas available, no chimney. He has been heating with a pellet stove, but works 10 hour days and has had problems with the unit (cleaning, staying lit, etc.). We'd like to replace the pellet stove with some type of central unit (the place is open concept and no place to put ducts, obviously). The question is, What type of heating unit? He doesn't need air conditioning ('cooler by the lake'). I've read some posts here about 'mini-splits' - don't know what they are, and we have considered a direct vent LP unit (he has an lp water heater). Advice?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    A mini-split is an air conditioner where the compressor is outside, and the fan and evaporator coil is inside, connected by two hoses for the refrigerant. These can be purchased as heat pumps strictly for heating purposes, or heating&a/c. It depends on how cold it gets there whether it would work as a reliable heating device on the coldest days. It would work fine for most of the year, probably...it all depends on how cold it gets on the typical coldest day.

    Not all pellet stoves are created equal...some have the ability to light themselves, hold a large quantity of fuel, and should work reliably for probably at least 24-hours...it would be an issue if you were going away for longer, so a backup plan would be required.

    There are a bunch of wall-hung, through-the-wall furnaces that can be run off LP.

    There are also some nice water heaters that are designed to also provide space heating...he'd have to put in some baseboard heaters or, better, find some refurbed cast iron radiators or low profile heaters. Those would provide a more even, comfortable heat that won't dry the place out like a forced-air system would, and when arranged properly, would provide a more even heat.

    Before you consider anything, though, you'd probably want to try to figure out the actual sized unit required...this is called a manual-j calculation. There are some free on-line calculators that aren't too bad, but a good analysis would require a pro with the right tools. The inputs required are the size, location and type of windows, the size and orientation of the cottage, the amount and type of insulation in the walls, floor, ceiling, and an idea of how air tight it is. Some work on making the place air tight would go a long ways towards minimizing the energy costs and improve the comfort radically for often a small investment.
  3. Dana

    Dana In the trades

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    A mini-split can almost certainly handle his heating & cooling loads, the question is only how big it would need to be to do the whole shebang. It would cost a lot less than heating with LP, possibly less than heating with pellets.

    Like wall-furnace solution it would take up some wall area, but not as much. The indoor heads look like this:

    [​IMG]

    The outdoor half of the unit looks like this:

    [​IMG]

    In a WI location it would be important to mount it above the record snow depth, bracket mounting it on the wall protected by overhangs is good practice- preferably under the rake of the roof rather than the eaves, to avoid having to dig it up after a big storm.

    At southern WI outside design temps it's probably better to go with the Mitsubishi Hyper Heating series or the Fujistu Halcyon "H" series, since those both have features designed for non-destructive operation down to -15F or so, with rated outputs at those temps. Others may have issues with defrost-water icing up in the bottom of the unit during extended cold snaps, potentially damaging the fan on the outdoor unit.

    Even a pretty crummy 600' house would likely be heated comfortably with a 1-ton like the Mitsubishi MSZ-FE12NA or the Fujitsu AOU-12RLS2H, but may be within the reach of the 3/4 ton units, the -FE09NA or the - 9RLS2H. In my neighborhood either of the 1-tons would come in about $4K installed, but a competent DIYer doing most of the installation and letting a qualified tech handle the final charge & test commissioning for a hundred or two could do it for a lot less. The hardware itself isn't outrageously expensive at internet pricing, eg:

    http://ecomfort.com/muz-fe12na-1-ms...-mounted-wireless-remote-12000-btu-26884.html

    http://www.greendroplet.com/index.p...ir-conditioner-26-seer-9-000-btu-3-4-ton.html

    http://www.greendroplet.com/index.p...air-conditioner-25-seer-12-000-btu-1-ton.html

    http://www.greendroplet.com/index.p...-conditioner-27-2-seer-9-000-btu-3-4-ton.html


    Got a zip code (for weather data) and a better description of the cabin & insulation levels, window size/type, etc (for heat load estimation)?
  4. Wet_Boots

    Wet_Boots Sprinkler Guy

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    Metro NYC
    Too bad about no chimney - an open 660 sq ft space could be handled with a coal stove.
  5. Dana

    Dana In the trades

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    A coal stove (even a small one) would likely be way oversized for the heating load, and wouldn't necessarily keep burning all day while the guy was at work, eh? (The pellet stove was probably oversized too.) But then, with a coal stove you'd want to keep the window open to mitigate the CO poisioning risk, eh? ;-)

    Direct vent LP wall furnaces and mini-splits are the best bets for finding something close to right sized that isn't a PITA to deal with. Assuming a 99% outside design temp of -5F (Beloit's is -3F, Milwaukee's is -2F) a 660' house with crummy R19s in the attic and crunched up poorly installed R11s in the walls, and at least storm windows over leaky single-panes will still be under 20,000BTU/hr, and may be under 15K:

    Assuming a perimeter of ~100' and 10' from the bottom of the floor joists to the ceiling, and R11s in the walls you have about 1000' of gross wall area with a U-factor of about 0.12. With an interior temp of 70F that's a 75F delta, so the wall-losses would be about

    U0.12 x 1000' x 75F= 9000BTU/hr

    Assuming 5 windows @ 10' each for 50' of windows with a U-factor of 0.5 you have window losses of:

    U0.5 x 50' x 75F= 1875 BTU/hr.

    With R19s in the ceiling, with framing-losses and convection -performance losses when it's -5F out you get a U-factor of about 0.08 for a ceiling loss of:

    U0.08 x 660' x 75F= 3960 BTU/hr

    Throw in 1000BTU/hr for a poorly weatherstripped 2" door, and another 2000 BTU/hr for floor losses you're still at only ~18,000 BTU/hr, which is within the rated output of a 1.5 ton cold-weather mini-split @ -5F. (Either an MSZ-FE18NA or AOU-15RLS2H would cover it.)

    If it's much tighter than that (or if it could be made tighter than that) you'd be within the output of a 1-ton. If it's 2x6 construction and there's R30 or something in the attic you could be within the output of a 3/4 ton.

    A pretty good ~21KBTU direct vent LP Rinnai would save a few hundred on in up-front hardware costs, but in most places would cost 2-3x as much to operate as a mini-split, and the difference could be made up in lower operating costs in at most 2 heating seasons (in less than 1 season in many locations- it depends on your electric rates and the local propane pricing.) And you wouldn't have to worry about running out of propane and having to wait for the delivery truck during a cold spell.

    Buck-fifty propane (the recent price average for propane in WI) burned in an 82% wall furnace delivers about 75,000BTU for $1.50 or $50/MMBTU. A pretty-good mini-split will have an average coefficient of performance of about 2.7 in that climate, delivering ~9000BTU per kwh over the course of a heating season. The average residential retail-delivered price of electricity in WI is about 14 cents/kwh, so the mini-split delivers heat at about $16/MMBTU, about 1/3 the cost of heating with a propane wall furnace. It would take 50 cent/gallon propane to match operating costs.
  6. Hunter01

    Hunter01 New Member

    Messages:
    15
    Location:
    Wisconsin
    Dana & Others:

    Thanks for the information. Dana - You're pretty close with your estimates - R11 walls, about right, but 8' ceilings; 9 windows - about 10' each, double pane, double hung, vinyl, no storms; R19 ceiling; he does have a decent little unheated porch, so it provides decent air lock on the entry door. Zip is 53040. Here's another small problem - 60 amp service. What does a one ton split draw? Probably have to have the service replaced. Not a bad idea anyway; about time. I certainly like the idea of cost of heating, but it DOES get cold here - sometimes (although not recently) -20 degrees.
    Thanks, again, I'll look into the split.
    Hunter
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    Yes, you'd want to upgrade the electrical service regardless of what you put in. Some of the minisplits work to -15F or so. There may be a couple that can handle a bit more. This is a far cry from what was available not that long ago, but mini-splits have been around for a long time - they just keep getting better.
  8. Dana

    Dana In the trades

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    The Mitsubishi Hyper Heating units turn themselves off to self-protect at about -20F, but automatically re-start when they get up to temp. The lowest tested-rated output is at -25C/-13F, but they're still putting out decent heat at lower temps until the controls self-stops. If that's a show-stopper, move on to the Fujitsu units.

    The Fujitsu xxRLS2H series just keeps on chugging no matter how cold it gets, but the heat of output isn't tested or guaranteed below -15F. Second hand beta from folks in the Adirondacks of NY say the the RLS2 (not -H) series is still putting out a decent amount of heat at -20F. The Fujitsu AOU-15RLS2 puts out about 17-18K @ -5F, and is probably a better choice than the 1-ton. It draws draws 6.1A @ 230V in heating mode, and even a 2-ton will usually be under 10A.

    I wasn't too far off with the -5F design temp, eyeballing the WeatherSpark dataset.


    So new napkin math:

    Walls, 8' x 100' for 800 square feet, for U0.12 x 800' x 75F= 7296 BTU/hr

    Windows 90' @ U0.5 (unless they're low-E, argon filled or something) for U 0.5 x 90 x 75'= 3375 BTU/hr

    Same 660' attic for 3960 BTU/hr

    Same crummy leaky door at 1000 BTU/hr

    Same 2000 BTU for floor loss fudge factors & random air leakage.

    Adds up to 17631.

    If you wanted to invest in low-E storm windows (the Larsen low-E storms sold through box stores are on the order of a couple hundred per, so it's not ultra-cheap, but it the payback is quicker than cheap clear-glass storms- should be under 5 years at the ultilty pricing & efficiencies we've been descussing.) A low-E storm enhances a U0.5 window into U0.28-U0.3 performance, peeling about 1400BTU/hr off the total.

    Any air-sealing you can do (including the holes for the pellet stove venting) can knock another 500-1000BTU/hr off it at VERY low cost, if you're the type of DIYer who can take it seriously. A ~20 square foot solid wood door has a U-factor of about 0.5, so with decent weatherstripping it would come in at 750 BTU/hr, not 1000, and that's probably not the biggest air leak in the place. The closed in porch probably takes 500-1000 BTU/hr off the whole thing if it's reasonably tight.

    You can take off another 250 BTU/hr per sleeping human, and another 150 for the refrigerator (unless it's on the closed-in porch, or IS the closed-in porch. :) ).

    The better than random guesstimate is you're looking at something on the order of ~15,000 BTU/hr @ -5F. A 1 ton like the -12RLS2H or -FE12NA would do, if you don't mind waking up to a house that's a bit under 65F on the very coldest nights, or want to install a 1500W (5000 BTU/hr) space heater or radiant cove-heater to cover the shortfall for when it's REALLY really cold. Cove heaters are cheap and provide very comfortable heat (way more comfortable than finned baseboards of similar cost), but if controlled via thermostat you'd want to set it for something like 65F when the mini-split is set much higher, so that it only runs when the mini-split really CAN'T keep up, (which should be less than 5% of the time even with a 1-ton.) Heat provided by the mini-split uses only about half the power of the cove heater even at -15F outdoor temps, and only 1/4 the power at +40F, so any resistance backup heat should be used only when needed. But the -15RLS2H or -FE18NA is probably going to be the better choices here. Both put out ~15,000BTU/hr at -15F outdoor temps, but 17-18K @ -5F, so they should handle the whole load most years, if not quite keep up during the cold-snap of the century.

    I think that's an -FE18NA compressor on the side of that green house in the picture. It's heating & cooling a whole ~1400' multi-story superinsulated house with some margin in a climate comparable to yours (Cambridge, NY), but the R-values are 3-4x those of your cottage.
  9. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    If the pellet stove inside a cottage is safe, so can be a coal stove. Same CO risk as with any combustion taking place within living space. No doubt a CO monitor is already in place. While nothing beats a masonry chimney, there are direct-vent coal stoves to be had.

    Direct-Vent and Power-Vent usage with coal stoves
  10. Dana

    Dana In the trades

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    Got a link to a manual on a direct-vent coal stove that has less than 30KBTU/hr of output? (Say, 2x oversized for the likely peak load or less.) The Harmans are 75KBTU/hr (4-5x oversized), the smallest Keystokers start at 125KBTU/hr (6-8x oversized.) They're not cheap either.

    And assuming you could find a suitably sized direct vent coal stove, why would you? I find it tough to believe that it would be any more reliable at staying lit than a pellet stove (particularly if it was way oversized and had be be run at the very bottom end of it's firing range to keep from turning the place in to a sauna.) The localized particulate & sulfur emissions issues surrounding coal burners isn't exactly a plus.

    And outside of coal country the fuel isn't always super-cheap & available either. There's little to no coal mining in WI:

    [​IMG]

    [​IMG]

    A low volume user in WI could easily be stuck searching for a reliable source at a reasonable price, (unlike much of PA/WV/KY coal mining regions.)

    The mini-split option (or even a direct vent LP burner) takes up less space, and heating without combustion or needing to handle & manage bulk fuel has it's advantages too. As long as the grid is up, you don't have to be concerned about keep the fuel supply up.
  11. Hunter01

    Hunter01 New Member

    Messages:
    15
    Location:
    Wisconsin
    Thanks, again for the help. I appreciate it, as well as your sense of humor: the refrigerator is IN the cottage, it's not the closed in porch. Glad I asked the initial question - I just have no experience with heat pumps or their ilk, even though I built my own house 20 years ago, and a different (our hunting) cabin about 25 years ago, so have some mechanical/building/electrical experience. Thanks, again

    Hunter
  12. Dana

    Dana In the trades

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    Something to keep in mind that may not be obvious: The high efficiency mini-splits are fully modulating systems large turn-down ratios, and they run at much higher efficiency modulating at part load than when cranking at full-speed. Most of the time it'll use less total power if you "set & forget" the temperature setpoint rather than turning it way down (or off) for the 10 hours you're away at work.

    And when sized close to the the margin so that it spends most of it's time modulating, if you use a large setback the recovery ramp getting back up to temp can be pretty long when it's actually cold out. Some people will set it back 3-5F for when they're away for the day or for sleeping, but it's not always going to save anything on the power bill- sometimes it'll save a little, but sometimes it's less than a break-even proposition. If going away for the weekend or something it'll make sense to set it back 10F or more, but hopefully it'll be warmer than -5F when you get back, or it could take several hours to bring it back up to temp. But if it's a balmy +25-30F out, the warmup ramp time is not much of a problem if the unit is sized for the -5F heat load, even from a 10F setback.
  13. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    I once rented a similarly-sized cottage, minus the open design. It used a 38,000 BTU direct-vent natural-gas heater. Thermostat was the old-fashioned metal bulb-and-tubing type that directly connected to the gas valve, which had a knob for setting the heat level. No power required, as the pilot light provided all the needed electricity by way of the thermocouple in the flame chamber. I think the brand name was Cozy. They also have LP models.

    I doubt there is one. It might be possible to apply a power vent to a standard coal stove. If there is a direct-vent unit in place, said vent could always be replaced with a more conventional steel chimney pipe, and one of the smaller "parlor stoves" could go to work. I've used one of the all-manual Franco-Belge stoves, with a top heat setting of 48,000 BTU (plus a just-in-case 15% boost setting) - top setting was rarely used, unless temps were low teens or less - at a more moderate setting, it could operate untouched for 12 hours or so.

    Of course, coal is regional in use, and the little stoves require anthracite, not the more commonly strip-mined bituminous coal.
    Last edited: Aug 8, 2013
  14. Dana

    Dana In the trades

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    Yeah, LP wall furnace type heaters are the only really other viable option here, but would cost 3x as much to operate as a lo-temp mini-split. A 38,000BTU hr unit would be 1.5-2x oversized for the load, but would still hit close to it's ~65-80% AFUE numbers. A hydronic heating loop running off a condensing propane HW heater would hit ~95%, but the expense of setting it up wouldn't be worth it given that mini-split solutions are cheaper, with much lower operating costs. In an off-grid situation some of the LP wall furnaces might make sense, but a tiny sub-40KBTU/hr soapstone wood-stove might be even better from an operating cost & comfort point of view. (They're not cheap either.)

    Burning high grade anthracite to heat a cabin would seem almost like a crime in some parts, and I doubt it's readily available anywhere in the midwest, and it still has significant local air pollution impacts. Coal stoves were resurging in popularity parts of New England back in the early 1980s, but got banned in most locations due to the sooty particulates. While wood stoves & pellet stove have similar issues, secondary burner technologies have taken the edge off that fairly dramatically.
  15. Wet_Boots

    Wet_Boots Sprinkler Guy

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    Anthracite actually burns very clean, compared to what enters the chimney of a wood stove. And at less than $200 a ton, it beats almost everything else for BTUs for the buck. There are some hard-core cheapskates using manual coal stoves that burn bituminous coal, and they even manage to avoid the purchase price of the coal, if they know where an open coal seam can be found, so they can have at it with picks and shovels. :) (their chimneys, I don't want to look at)

    Cozy has some 20K BTU units, if that's determined to be enough for the required heat, but a heat requirement that low, in the 17K BTU range, could be handled by way of electric baseboard, even on 60 amp service. At 3.412 BTUs per Watt, you would need less than 5000 W to get 17K BTU, a bit over 20 amps on 240. Electric baseboard would probably be the last choice, if power rates were high. I did see some homes convert to it when heating oil and natural gas prices shot through the roof a few years ago.
  16. Tom Sawyer

    Tom Sawyer In the Trades

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    What brand is his pellet stove.
  17. Hunter01

    Hunter01 New Member

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    15
    Location:
    Wisconsin
    OK, guys - Need some help, again

    I purchased and installed a 15RLS2H system from Fujitsu and did 90% of the installation myself. Today, I had a HVAC guy come over and hook up the line set, vacuum the lines and release the refrigerant (things I couldn't do myself.) We powered up and used the remote to attempt to start the unit. The indoor unit opened up, and fan started, but that was it. Outdoor unit didn't start, and it obviously wouldn't produce any heat. We looked at the troubleshooting guide, and, if you're familiar with the unit, at the end of the troubleshooting guide, it says: "If the problem persists after performing these checks, or if you notice burning smells, the OPERATION indicator lamp and the TIMER indicator lamp flashes, and the ECONOMY indicator lamp flashes fast, immediately stop the operation, turn off the breaker and consult authorized service personnel." This is exactly our condition, and the HVAC guy had no clue. We checked power and other obvious things to no avail.
    HELP! Any suggestions??
  18. Hunter01

    Hunter01 New Member

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    15
    Location:
    Wisconsin
    Well, I tried this yesterday, but it apparently didn't post, so here goes, again:

    So, I bought a Fujitsu 15RLS2H system and did 90% of the installation myself. Yesterday, I had a HVAC guy come over and connect the line set, vacuum the lines, and release the refrigerant. (Things I thought I shouldn't or couldn't do myself) We powered up, the indoor unit opened like it should, and the fan started. Then, nothing. (No action from the outdoor unit) We went through the trouble shooting guide, to no avail, and at the end of the guide, it says: "If the problem persists after performing these checks, or if you notice burning smells, or the OPERATION indicator lamp and the TIMER indicator lamp flashes, and the ECONOMY indicator lamp flashes fast, immediately stop operation, turn off the electrical breaker and consult authorized service personnel." That's exactly what the indicator lamps are doing (no burning smells, thankfully) My HVAC guy didn't know what to do, so, any suggestions (short of calling, now, an authorized dealer who would, hopefully, know what he's doing)
  19. Dana

    Dana In the trades

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    Is there a Fujitsu distributor available who will talk your HVAC guy through it? It's a brand new unit, they should be willing to provide tech support to a qualified installer.

    The RLS2-H series is new, but it's based on the tried & true RLS2 (no -H). Hopefully this isn't your HVAC guy's first mini-split.
  20. Hunter01

    Hunter01 New Member

    Messages:
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    Location:
    Wisconsin
    Dana - I emailed Fujitsu's tech service dept and they came up with the answer in their first try! Something I could do myself. So, as of this afternoon, we're making heat 'out of thin air'!!! It's awesome! My son and I are in your debt. If you ever need advice on human resources, carpenter work, or deer hunting, let me know! :) This is a great site which I have used to my benefit a number of times.

    Have a great day!
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