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new construction heating advice wanted

leeelson
leeelson Member Posts: 2
Looking for advice. Building a 2700 sq ft vacation home in rural Northern Vermont. Home will be used about a month by up to 10 people, mostly in the summer but occasionally in winter (temps down to -20 F). Need to keep house from freezing in winter. Only utility is electrical ($.19 kwh) but could install propane. Will have efficient wood stove. For cooling in summer, plan to use Mr. Cool heat exchange system. This can supply some heat also but efficiency drops with temperature, so likely not sufficient for vacant winter low level freeze protection. Ample room in basement.

Questions:
1)For water heating (including possibly radiant heating) I assume propane makes more economic sense and heats faster.
2)Water heating for 2 bath/showers and dishwasher could be (2?) tankless water heaters. Do these require more maintenance than other methods? Is one large heater better than 2 smaller ones given distribution requirements?
3)Are tankless water heaters good for radiant heating system or would it make more sense to do a boiler, possibly with an indirect water heater tank?
4)Is there another option that would be better?
5)Any sizing suggestions?

Comments

  • Hot_water_fan
    Hot_water_fan Member Posts: 1,005
    edited October 2022
    1). Electricity is substantially cheaper than propane right now for central and water heating in the northeast. The electricity $/MMBtu equation is: $/kwh x 293 / COP and propane is $/gal x 10.92 / COP. So about 60% cheaper to use a heat pump vs propane based on current prices. You could use the mr cool system or a professionally installed heat pump system. 
    2). A combi boiler (looks like a tankless heater but is made for central heating and DHW) can do both hot water and central heating, but must be sized for hot water usage. So it’ll depend on how many simultaneous showers you’ll have.  
    3). Size the central heating to the heat load, unless it’s a combi then size to the DHW. 
  • Paul Pollets
    Paul Pollets Member Posts: 3,568
    You would need to have glycol in the boiler for freeze protection. Many use furnaces because they don't need frost protection. The domestic water also needs draining when the house is unoccupied in cold months. A boiler and HW system is more comfortable, but will require some planning to make it work to expectations.
  • hot_rod
    hot_rod Member Posts: 18,195
    Depends a bit on what type of heating system you install. If it is radiant, requiring supply water below 120, an air to water heat pump may be the least expensive to operate. Some brands can now do DHW and heat.
    If it is a higher temperature hydronic like panel rads or fin tube, or air coil you want a boiler. I like combis for heat and DHW in one component.

    You need to look at fuel cost in your exact location. Then look into the crystal ball to see where prices will be down the road :)

    As you can see the heat pumps, properly applied, are often the lowest operating cost.

    There is a heat pump buffer tank that has a back up electric element, so you could still get some heat if the HP fails.
    Assuming the power stays on :)

    https://coalpail.com/fuel-comparison-calculator-home-heating
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TAG
    TAG Member Posts: 738

    1). Electricity is substantially cheaper than propane right now for central and water heating in the northeast. The electricity $/MMBtu equation is: $/kwh x 293 / COP and propane is $/gal x 10.92 / COP. So about 60% cheaper to use a heat pump vs propane based on current prices. You could use the mr cool system or a professionally installed heat pump system. 

    2). A combi boiler (looks like a tankless heater but is made for central heating and DHW) can do both hot water and central heating, but must be sized for hot water usage. So it’ll depend on how many simultaneous showers you’ll have.  
    3). Size the central heating to the heat load, unless it’s a combi then size to the DHW. 
    At .20kw and Propane at $2.50 .... heatpump with COP above 2 wins.
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,005
    @TAG plus the EIA has northeast propane at $3.50!
  • WMno57
    WMno57 Member Posts: 663
    Check out Joe Lstiburek's designs for cold weather homes. On new construction I would have foam boards completely surround the outside of the basement. Floor, footers, walls, all the way up to the sill plate. Spend a lot of money on insulation. Whatever you were planning to spend on insulation and sealing, suck it up and spend more.
    https://www.buildingscience.com/users/joseph-lstiburek
    Pex for domestic water.
    Shut off water ever time you go away.
    Have drains in basement for domestic water. (never know when you might need them)
    Don't put kitchen and bathroom sinks on outside walls.
    Automated fresh air system (forget the word for this).
    I think a good heat pump will work well for most of the year. It is six of one, half a dozen of another wither you go all electric or not.
    Me personally, I would have propane for a backup generator and a backup propane forced air furnace that is part of the heat pump system.
    Assume a well? Get a 5 to 10 KW permanently install genset with a transfer sub panel. 1800 rpm 4 pole if you can find one. I would not get a whole house generator, and I would not configure for automated transfer. That could completely drain your propane tank unattended. Don't undersize or oversize the genset.
    YOU WANT A BASEMENT. SLABS AND CRAWL SPACES ARE FOR THE SOUTH!

    Paul PolletsLarry Weingartenkcopp
  • TAG
    TAG Member Posts: 738
    edited October 2022
    We had a place in Stowe for many years .... building new the cheapest and best thing you can do is build it correctly with the best insulation you can afford.

    There are just too many variables .. the fact that you want to use it at all in the winter makes big changes.

    All electric is easy .. but, can have high running costs depending on use.
  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    Passive solar, dang it! If you are building new, there is absolutely no excuse -- unless your site is deep in a valley -- for NOT going passive solar.

    It does take some thought and an intelligent architect to heat a house in northern Vermont to 70 solely by passive solar, I'll grant that. However, it can be done -- I've done it. To heat a house to the point where a decent wood stove will bring it up when you come in the winter is easy. That would be to hold it at no colder than say 50 when you are away.

    The house doesn't even have to look weird or out of place, although it is easier to do if it is a more modern design.

    Nor does it have to be significantly more expensive to build than any well built structure.

    Which brings up the next point: Don't cheap out on the build. Yes, insulate it heavily. That's a must -- for any heating approach. But watch your construction: insulation is no substitute for poor workmanship which results in multiple, if small, air leaks in the envelope. Your builder doesn't have to be a fanatic, just a very good and conscientious craftsmen, paying attention to details. They do exist.

    Which introduces the next point: true 100% passive does have some problems; the two most difficult are solved in the same way. Cheat. The two are a lack of indoor air exchange and the problem of overheating on brilliant winter days with good snow cover. The solution to both is to provide a heat recovery (NOT energy recovery) ventilator with a low speed high volume fan and minimal ducting. That takes it out of the 100% passive (there's that fan) but is easier than doing the same thing entirely with gravity air circulation (which is feasible, but gets fussy).

    OK. That gets rid of the heating problem.

    It also gets rid of the problem of freeze protection if something fails. There's nothing to fail, and the house won't freeze.

    Now domestic hot water. You really have four options. LP fired storage water heater, LP fired on demand water heaters (probably two, unless your plumbing is very concentrated), electric storage water heater, and heat pump water heater. Each has advantages -- and disadvantages. The "greenest" is the heat pump water heater, but only if it is set up so the electric resistance fast recovery mode can be disabled. The flip on that is that on heat pump only, recovery is very slow, so it will have to be big enough in terms of storage alone to supply all the hot water (multiple showers, etc.) that you expect to have in a time span of eight hours or so. They also are very expensive. The only real advantage I can think of for conventional electric storage water heaters is that they are cheap to purchase. That leaves LP fired storage and LP fired on demand. These will both cost about the same to run. The storage will cost less to buy, but recovery is good so it doesn't need to be outrageously large. LP on demand has a good deal to be said for it. The only real problem I've run into with it is that it is not uncommon for it to be undersized, particularly in cold climates. Be sure that it or they have enough capacity for all the fixtures you remotely think of using together can indeed run together -- and that that capacity is at the temperature rise you are expecting to need (they are commonly rated for a 60 degree or so rise -- 50 F incoming water. You are likely to have 32 F incoming water in the winter, which would need a 90 degree rise to be usable, or to look at another way, half again the output in the advertising. If I were to do it, I'd likely go with LP on demand -- but I like my hot water hot, and plenty of it.

    As an aside, why not solar domestic hot water? Much too fussy. Freeze problems. Big storage tanks.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Larry WeingartenBobZmuda
  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    And PS -- please feel free to PM me if you want more information on passive solar, or just other questions.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,936

    new construction heating advice wanted


    Can I ask for wheelchair access to the pool and a first floor bedroom? PM me the address and when house might be completed and vacant so I can crash there and relax. Promise to leave the house as clean as I found it! Can't guarantee I won't drink any beer you leave there.

    Otherwise any type of heating system will be acceptable for my needs.

    Thanks
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • WMno57
    WMno57 Member Posts: 663
    One of my favorite sites on the web. A blog describing the construction, power systems, and life at an off grid home in Michigan's Upper Peninsula. Three miles from the nearest electric.
    https://offgridcabin.wordpress.com/

  • Hot_water_fan
    Hot_water_fan Member Posts: 1,005
    A positive I can think of for a cheap resistance domestic water heater is that the place will be mostly empty. Who cares if it’s less efficient if it’s off? 
  • hot_rod
    hot_rod Member Posts: 18,195
    Search around for net zero and passive homes in Vermont. Plenty of track record that they work.

    Mini splits and PV can get you to net zero with a bit of a wood stove perhaps.

    Use this site to get incentive info. After the first of the year new federal will be available
    www.dsireusa.org

    https://bensonwood.com/portfolio/vermont-passive-house/
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TAG
    TAG Member Posts: 738
    hot_rod said:

    Search around for net zero and passive homes in Vermont. Plenty of track record that they work.

    Mini splits and PV can get you to net zero with a bit of a wood stove perhaps.

    Use this site to get incentive info. After the first of the year new federal will be available
    www.dsireusa.org

    https://bensonwood.com/portfolio/vermont-passive-house/

    That guy made a kit for me when he was just starting out. They did timber frames. Project was in PA near a well known trout steam in the very late 80's
  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    edited October 2022
    TAG said:

    hot_rod said:

    Search around for net zero and passive homes in Vermont. Plenty of track record that they work.

    Mini splits and PV can get you to net zero with a bit of a wood stove perhaps.

    Use this site to get incentive info. After the first of the year new federal will be available
    www.dsireusa.org

    https://bensonwood.com/portfolio/vermont-passive-house/

    That guy made a kit for me when he was just starting out. They did timber frames. Project was in PA near a well known trout steam in the very late 80's
    They are one of the better outfits -- but there are a few others and, as I say, an intelligent architect can do very well also. In a way, it's not totally unlike steam in one regard: build quality is almost as important, if not more so, than design.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • WMno57
    WMno57 Member Posts: 663

    A positive I can think of for a cheap resistance domestic water heater is that the place will be mostly empty. Who cares if it’s less efficient if it’s off? 

    Keep hot foods hot, and cold foods cold.
    Legionella.
    Now if someone made a control that would jack up the temp to 140 and circulate that through all the pipes every week unattended. Hmmmmmmmmmmmmmmmmmmmmmmmm. That would need a good marketing name. The PasteurBot.
    Hot_water_fanLarry Weingarten
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,005
    Keep it on then. Idle loss is very low for electric tanks :) 
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,782
    edited October 2022
    Hi @leeelson , Now is the only real opportunity to get the shell right. Consider SIPS, thicker than people tell you makes sense. They make it easy to build a tight, very well insulated, vapor resistant, and structurally sound home. Also, insulate down 3-4 feet along the perimeter and "earth couple" the home. Here are some fancy ways of doing that: https://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger . The un-fancy way is to simply put a slab on top of the insulated ground under the house. The ground acts as a very big thermal battery, trying its best to maintain the average year-round temperature.

    A trick for cooling in summer is to run a fan that pulls air from the highest, hottest places in the house, and runs it through pipes in the soil to cool it down. Drains need to be placed at low points so water cannot build-up in the buried line. That heat winds up helping you in cooler times of year. This can be very helpful when it's -20F outside! Reading this thread, I think you've been given a lot of good advice based in hands-on experience.

    Yours, Larry
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,084
    Jamie hit the nail on the head.... Passive solar. Nothing to break down. I'm in Northern Illinois and built my 24 x 34 garage with 2x6 walls, r-21 and r-30 in the ceiling. I had the interior drywalled using airtight drywall technique. , but hadn't finished taping the ceiling seams. I insulated down 4 feet at the footings and the garage floor was insulated ( I planned on running radiant floor). We had 3 about 4 foot x 6 foot standard thermopanes on the southside with full solar exposure. Over the 2 winters we owned the home, I kept a gallon jug of water on the garage floor and it never came close to freezing. 70 Sq ft of passive solar was enough to keep the 800 Sq ft space warm ( along with ground coupling). If I did it again I would leave the slab uninsulated for better ground coupling since I never needed the floor heat.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,084
    Just a quick addition to the above..... A sensible, balance solution would probably be to design for passive solar to heat the house at -20F and the interior around 45F so the home will be heated when not occuppied without any additional energy. Then use a conventional system to add the heat needed to make it comfortable when occuppied. During typical more moderate winter weather, you may not need any supplemental heating even when occuppied.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    Or use the wood stove... thank you for the endorsement, @The Steam Whisperer ! (oh -- and it's amazing how much solar gain one gets from even normal windows -- the mass in your floor stores the heat when the sun sets or its cloudy. Really folks, it does work!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 18,195
    If you go passive, beware if too much of a good thing. Without proper roof design or control, summers in a passive home can be unbearable. 

    The roof  shading and possibly operating window shades need to be considered.

    We fought overheating passive sunrooms for many years in the Utah mountains,  You don’t want to end up with AC bills larger than the heat energy you save.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • leeelson
    leeelson Member Posts: 2

    Passive solar, dang it! If you are building new, there is absolutely no excuse -- unless your site is deep in a valley -- for NOT going passive solar.

    It does take some thought and an intelligent architect to heat a house in northern Vermont to 70 solely by passive solar, I'll grant that. However, it can be done -- I've done it. To heat a house to the point where a decent wood stove will bring it up when you come in the winter is easy. That would be to hold it at no colder than say 50 when you are away.

    The house doesn't even have to look weird or out of place, although it is easier to do if it is a more modern design.

    Nor does it have to be significantly more expensive to build than any well built structure.

    Which brings up the next point: Don't cheap out on the build. Yes, insulate it heavily. That's a must -- for any heating approach. But watch your construction: insulation is no substitute for poor workmanship which results in multiple, if small, air leaks in the envelope. Your builder doesn't have to be a fanatic, just a very good and conscientious craftsmen, paying attention to details. They do exist.

    Which introduces the next point: true 100% passive does have some problems; the two most difficult are solved in the same way. Cheat. The two are a lack of indoor air exchange and the problem of overheating on brilliant winter days with good snow cover. The solution to both is to provide a heat recovery (NOT energy recovery) ventilator with a low speed high volume fan and minimal ducting. That takes it out of the 100% passive (there's that fan) but is easier than doing the same thing entirely with gravity air circulation (which is feasible, but gets fussy).

    OK. That gets rid of the heating problem.

    It also gets rid of the problem of freeze protection if something fails. There's nothing to fail, and the house won't freeze.

    Now domestic hot water. You really have four options. LP fired storage water heater, LP fired on demand water heaters (probably two, unless your plumbing is very concentrated), electric storage water heater, and heat pump water heater. Each has advantages -- and disadvantages. The "greenest" is the heat pump water heater, but only if it is set up so the electric resistance fast recovery mode can be disabled. The flip on that is that on heat pump only, recovery is very slow, so it will have to be big enough in terms of storage alone to supply all the hot water (multiple showers, etc.) that you expect to have in a time span of eight hours or so. They also are very expensive. The only real advantage I can think of for conventional electric storage water heaters is that they are cheap to purchase. That leaves LP fired storage and LP fired on demand. These will both cost about the same to run. The storage will cost less to buy, but recovery is good so it doesn't need to be outrageously large. LP on demand has a good deal to be said for it. The only real problem I've run into with it is that it is not uncommon for it to be undersized, particularly in cold climates. Be sure that it or they have enough capacity for all the fixtures you remotely think of using together can indeed run together -- and that that capacity is at the temperature rise you are expecting to need (they are commonly rated for a 60 degree or so rise -- 50 F incoming water. You are likely to have 32 F incoming water in the winter, which would need a 90 degree rise to be usable, or to look at another way, half again the output in the advertising. If I were to do it, I'd likely go with LP on demand -- but I like my hot water hot, and plenty of it.

    As an aside, why not solar domestic hot water? Much too fussy. Freeze problems. Big storage tanks.

    First, thanks for taking the time for a detailed reply. Very useful.

    17 years ago we built a passive solar house with solar hot water and photovoltaics. I did the energy design myself using the DOE Energy 10 program (which I still have). We live in a cold climate (not as cold as Vermont) and the result was amazing. Temps today were 24-48. House was 69-77. Partly cloudy. No added heat. We have wood (masonry heater) as a backup and natural gas after that (heating index ~ .9 BTU/degree-day per square foot).
    So I'm totally on board with passive solar. The problems are manyfold for the current site. Mountain to the south and west, heavily forested (mostly but not all deciduous) so there is significant shading, even in winter. Enough to make domestic solar hot water impossible in the summer and spring. Also, the (to die for) view is to the east. The footprint is somewhat restricted by the state and township, i.e. an east west axis would not be allowed due to constraints. This house is being built by committee, not all passive solar diehards like me. That being said, we do plan more east facing windows than north and, (perhaps most important) we're planning double pane windows and cellular shades with side tracks and as much insulation as we can afford.
    One thing I learned living in a passive solar house for many years is that there is a fair amount of manual adjustments that must be made for optimum performance. A good example is the shade operation: hard to automate given that shades down in direct sunlight can break window seals (or worse) and shades up at night cause more net heat loss over 24 hours than if the window were not there at all. This type of maintenance does not lend itself well to a vacant house.
    I also know that mother nature can be quite wicked at times. I seriously doubt that you or anyone else can keep a home in Vermont at 70 without added heat if there is a week of overcast/storms and sub-zero temps. You can't change physics. If I'm not there, I may find some serious damage when I return.
  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    Camel: a horse designed by a committee.

    @hot_rod 's comment about shading is important; that's why you really need an architect or experienced designer to help out some. However, if it is done carefully, you don't need the kind of manual adjustments you mention, at least not to keep within say plus or minus 5 degrees of where you really want to be.

    Do not be fooled by domestic hot water -- it takes much more care in orientation and exposure than passive solar heat does. While an east to west orientation for a nice big glass wall is optimum, it's by no means mandatory. If there is an opportunity for considerable glass in an east facing exposure, that will go a long way. There are two main aspects to successful passive solar design. The first, obviously, is collecting enough sunshine. With careful construction and very good insulation you should be able to get the heating load down to around 50,000 BTUh, even on the coldest nights. That's around 14 kilowatts, but that's over the whole day, and the sun doesn't shine for 24 hours! A convenient estimate I've used is that, on average, one will get about 3 hours of sunshine per day in your climate (some days more, some days less) so you need to be able to get about 120 KW of power while the sun is shining. That takes 1200 square feet of glass. But that's holding about 70; if you want the solar to provide the base load -- say hold 50 -- that drops to about 900 square feet. But that doesn't have to be all one big glass wall! As long as it's there, somewhere, and the sun is shining on it you're good.

    The other key, as @The Steam Whisperer hinted, is storage. LOTS of storage. And the best way to get that in most cases is concrete and masonry. Mass concrete floors are great. So is, if your committee would tolerate it, the use of concrete for some or all of the exterior walls and even some of the interior partitions, possibly faced with something more elegant. The exterior wall concrete must, of course, be INSIDE the insulation!. The heat capacity of concrete is around 30 BTU per degree Fahrenheit per cubic foot, so if the concrete is allowed to drop form 70 to 40, that's almost 1000 BTU of storage per cubic foot of concrete. A two foot thick floor in your situation would drop to 40 from 70 in about 4 days, for instance, assuming NO solar input in that time.

    No, it won't stay at 70 and you'd have to be daft to suggest it could. But it will stay above freezing for your week of miserable weather.

    Where is this, by the way? Up near Jay perhaps?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • TAG
    TAG Member Posts: 738
    I was going to say ... VT can be cold and overcast in the winter.

    With 10 people regularly -- get an on demand water heater. I have a dedicated one at my beach house for the outdoor shower ... nothing else would keep up. Mine is natural gas because we have it.

    Propane vs electric --- electric is 2x the cost of Propane at $2.50 ( I paid last month). That's if you own the tank and use enough.

    Modern heat pumps really work .... a high end heat pump w/ propane furnace makes for a nice set up. That's what I installed in my last project .. the place also has full radiant w/ boiler for when we are there for extended lengths of time (I'm an HAVC nerd)




  • Hot_water_fan
    Hot_water_fan Member Posts: 1,005
    edited October 2022
    Seems much easier and cheaper to install only as many windows as you visually desire and insulate, air seal, and use a hybrid ducted system. You can get a nice low heat loss and if you’re setting back the house while you’re gone, you can knock usage down even more. Heat pumps perform better when outdoor temp is closer to indoor temp, so you can outperform the rating. If your annual heating usage is 50-100MMBtu, which it roughly should be, you’re not spending much on heat and the high mass passive solar juice isn’t worth the squeeze, have you seen the price of concrete recently? Solar PV is another story, would probably pencil well! 

     @TAG the poster said electric was $.19/kwh. That’s about 40% cheaper than propane at $2.5. Makes little sense to burn propane unless absolutely necessary (I think including it makes sense for backup/cooking/propane fireplace, etc.). 
  • Jamie Hall
    Jamie Hall Member Posts: 20,439
    For my benefit -- as much as our OP here -- what heat pumps have a COP of better than 2 at -20F?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,005
    For my benefit -- as much as our OP here -- what heat pumps have a COP of better than 2 at -20F?
    Zero I assume. How’s that relevant? 
  • TAG
    TAG Member Posts: 738

    Seems much easier and cheaper to install only as many windows as you visually desire and insulate, air seal, and use a hybrid ducted system. You can get a nice low heat loss and if you’re setting back the house while you’re gone, you can knock usage down even more. Heat pumps perform better when outdoor temp is closer to indoor temp, so you can outperform the rating. If your annual heating usage is 50-100MMBtu, which it roughly should be, you’re not spending much on heat and the high mass passive solar juice isn’t worth the squeeze, have you seen the price of concrete recently? Solar PV is another story, would probably pencil well! 

     @TAG the poster said electric was $.19/kwh. That’s about 40% cheaper than propane at $2.5. Makes little sense to burn propane unless absolutely necessary (I think including it makes sense for backup/cooking/propane fireplace, etc.). 

    You must be plugging in a heat pump in the price/ usage converter. Propane is cheaper than resistance electric at my numbers ... it's not going to be w/ a heat pump above 2 COP. The OP wants hot water and enough for 10 people ... that's a lot of hot water. With a vacation house it's going to require two big tanks -- sort of dumb unless he has a lot of extra space for them. I'm not in love with on-demand -- they are OK if planned for when building new and you can keep them close to the needed outlets.

    Mini-splits are great problem solvers ... long term planning new I still like proper ductwork for a typical house.
  • Jamie Hall
    Jamie Hall Member Posts: 20,439

    For my benefit -- as much as our OP here -- what heat pumps have a COP of better than 2 at -20F?
    Zero I assume. How’s that relevant? 
    Because that's when you need backup heat in northern Vermont -- and I just don't think a heat pump is going to be a happy camper.

    If solar isn't going to do it all -- and on aesthetic grounds I'll grant it may not be, in short answer to the OP's question I'd go with LP hot water, radiant floors and additional radiators as required. I'd go as much solar as I could get away with, to reduce or eliminate the freeze problem (see comments above).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,005
    edited October 2022
    Agreed, LP should be used as the backup. Since OP wants AC and won’t be there much in the winter, a heat pump and propane hybrid seems the best of both worlds for central heating. And as many properly placed windows as desired.  We’re in agreement @Jamie Hall!

    You must be plugging in a heat pump in the price/ usage converter. Propane is cheaper than resistance electric at my numbers ... it's not going to be w/ a heat pump above 2 COP. The OP wants hot water and enough for 10 people ... that's a lot of hot water. With a vacation house it's going to require two big tanks -- sort of dumb unless he has a lot of extra space for them. I'm not in love with on-demand -- they are OK if planned for when building new and you can keep them close to the needed outlets.
    I’m talking central heating not DHW. You’re right about resistance being more expensive. I think either propane or electric would be fine for DHW since it's not lived in 24/7.