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Comfort, radiant heating vs forced air (minisplits)?

Davor Radman | Posted in General Questions on

I am biased. I grew up in an insulated (for the time era, but still very leaky) house with hydronic. It’s really comfortable. We don’t really get warm feet per se, but it’s not unpleasant to sit on the ceramic tiles without a carpet. I really like it.

Right now I live in another leaky house with weaker insulation, with panel radiators. it’s noticeably less comfortable.

Between these two, hydronic 100/100 times.

But problem is, I have never in my life been to a house that has forced air heating in the dead of winter.

So I have a few questions:

1) How much unpleasant can blowing/moving air be?

2) How is the noise? for some middle-of-the-road units?

3) How often do these turn on in a “pretty good house” with low thermal loses?

4) if the house is 1700sqft with “pretty good house” level of insulation, do walls and floors ever get nearly as warm as when hydronic heating is used?
I know that with good insulation there is no “warm feet” in hydronic system, but with panel radiators where I live now, tile floors in uninsulated ground floor are cold. Would simply insulating under slab help with this?

5) how many indoor units would I need, if there is a living space + 1.5 bathrooms + 4 bedroom + reading/work room? So, 8 rooms that need to be heated in total. Taking into account that there will be ducted ventilation, so air is moving around the house.

6) PTV is than resistance electric?

2 minisplits with 8 indoor units are still cheaper than hydronic + gas installation. Even if we do not take into account that I would need 1+2 mninisplit for summer cooling.
Running costs would probably be lower for minisplits as well, with gas being 1/3 / kwh of electricity, and average oct-april temp being 40-45 f.

I really like the idea of minisplits, aesthetics be damned, but comfort is a make or break factor for me.

I know there are great articles about radiant, minisplits and some QA posts, but perhaps there is some new development?

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Replies

  1. Ben Balcombe | | #1

    In my 8 years living in New England I've spent 7 of them in homes with central air and just this last winter in a home with hydronic baseboard and I much prefer the latter.

    We had a new construction 'energy star' home with contractor grade forced air and during the heating season we would have what I'd call the cyclical heat. By that I mean the air temperature drops below the set point on the thermostat, heating kicks in, the room warms up until the heat turns off and then the warmth slowly rises to the point where you're sitting in the cold and the air temp at the thermostat hasn't quite dropped below the set point again, until it does and the cycle repeats.

    Hydronic baseboard with a wood stove makes for a much nicer living environment, even in the 30 year old home we're currently renting.

    From asking similar questions on this very site, my understanding is that a properly sized and installed system, using quality equipment in a well sealed and insulated home leads to a completely different experience. Especially with the latest mini-split systems that can vary their output down to a couple of thousand BTU just to keep a gentle flow of heat into the home.

    If I think back to the HVAC install in our 'energy star' house, it was all flexible duct with lots of knifing and the second floor system, even though zoned, was a single speed blower 'sized' for the full ~1400 sq/ft which meant that when only one zone was calling for heat it was getting a full gale of air through the registers.

  2. Stephen Sheehy | | #2

    I can give you my experience in Maine. Two years ago, we moved from a house with radiant floors into a new, Pretty Good house with two minisplits. The new house is tight and well insulated. Design heat load (at 0 F) is about 12000 btu/h.

    Our finished floors are concrete and are certainly not warm, but are also not noticeably cool either. We have 4" of reclaimed XPS under the slab. In our old house, we'd get the toasty floor, but only when the heat was on and if we got solar gain during a sunny day, we didn't need heat so the floors ended up at ambient air temp. The slow response of radiant heated floors is a negative factor.

    We have two minisplits, one in the great room of about 700 square feet and one in the master bedroom suite of about 450 square feet. The minisplits are quiet. You don't notice air blowing around unless you stand under a unit and even then, it's barely noticeable. We leave the fan set to auto.

    The current outside temp is 26 F and it's cloudy. The bedroom unit is shut off. The great room remote is set at 72 and the air temp is 72. The unit isn't noticeably running at the moment, so it's either off or operating at a low level. Bedroom is 70 even though the unit is shut off. The spare room/TV room/office/ guest room (about 225 square feet) is about 69.

    Last year we shut off both units in early April. We used both a bit for AC in the summer. In April and May, even with temps sometimes in the 40s at night, the house stayed comfortable, so I think the key is a good building envelope. We get lots of solar gain on sunny days this time of year.

    I can't imagine you'd need a head in every room, but a room by room manual J will help decide where to put units. We leave the interior doors open all the time, so the heat gets pretty evenly distributed.

    At your typical winter temps, minisplits would be very efficient. Here in Maine, even when it gets well below zero, the minisplits have no problem keeping the house warm.

    As for aesthetics, the units are wall mounted about 9' above the floor and hardly noticeable.

    All in all, we are very happy with the minisplits. I'd never want radiant in a well insulated, tight house. In any but the coldest times, the slow response would be a big negative. A couple of minisplits are much cheaper than the typical radiant system.

  3. Richard McGrath | | #3

    Davor,

    Not sure if these are still considered a new development or not but you do not necessarily need mini splits also for summer cooling .
    This panel rad type fan convector is able to provide heat and cooling through one unit . It also offers room by room zoning without complex controls . An HE water heater can provide your heating water using only 2 ECM circs and a flat plate heat exchanger to keep DHW water and heating fluid separated from each other . A quality residential sized chiller unit provides the cooling fluid , due to the small tank in a ChillKing unit the equipment will also not short cycle . Comfort , efficiency , lower first cost than what others will recommend / specify . You will also be capable of utilizing outdoor reset strategy for heating . No boiler needed for low temp heating operation , this saves plenty of money .

    http://www.htproducts.com/fan-coil.html

    http://www.chillking.com/specpage/HORIZONTAL/GC24CK1.pdf

    http://www.chillking.com/specpage/VERTICAL/GV18CKB1.pdf

    Any water heater that is approved for space heating also will be capable . Mind you that a water heater used for hydronic applications should include the heat exchanger for health and safety purposes . I do suggest a modulating / condensing H2O heater . HTP manufactures 3 water heaters (tank type , 20-120 gallon , 1,600.00 / 5,000.00) that would be more than capable of this function . The theory that the heater knows whether it is flowing through an air handler coil or piping to multiple terminal units is silly .

    http://www.htproducts.com/literature/RGH75100-brochure.pdf

    http://www.htproducts.com/literature/lp-191i.pdf

    You could also just choose a Chiltrix unit along with their similar ( i think identical ) fan convectors which heating and cooling would be done by a single outdoor unit . In either case in this crazy world when refrigerants change and / or become obsolete you can just replace the outdoor units as opposed to the very real possibility of changing outdoor / indoor equipment both because of compatibility issues .

    If first cost is your only concern above comfort and efficiency that may be your driving factor . If you are looking to have everything you want without compromise you should really look into other than what everyone and their cousin is shouting about . truth is that everything the air based crowd has done , is doing , will continue to do is all based on one thing , attempting to be as efficient and comfortable as the very first heating systems , HYDRONIC .

    There is much to be said about having heat / cool where and wehen you want it and not playing a shell game about someone's knowledge about air flows , zoning and how well it will work . that is a fools errand .

    Do not forget that no matter what you get a room by room heat loss calculation will be necessary . Variable water volume and variable water temp will always be better than VRF alone . R718 just plain offers more value than any other refrigerant , the environmentally friendliest refrigerant .

    http://www.r718.com/articles/3451/the_basics_of_r718_water_vapour_compression_br

    Good Luck

  4. GBA Editor
    Martin Holladay | | #4

    Davor,
    As Stephen Sheehy's post confirms, the main factor determining occupant comfort is the quality of your home's thermal envelope. If the envelope is relatively airtight -- without much infiltration and exfiltration; if the R-values are above code minimum values; and if the windows are high-performance windows; then the occupants are likely to be very comfortable, regardless of the type of heating system that is installed.

    If the house is leaky and poorly insulated, and the windows are cheap, it doesn't matter how the place is heated and cooled. You'll be uncomfortable.

    So spend your money on the envelope. Don't worry about the heat delivery system.

    -- Martin Holladay

  5. Bob Irving | | #5

    I've built several "pretty good houses" with mini splits, so when I wanted to stop hauling and burning wood and using my loud and obnoxious, old hot air furnace, we started working on the envelope; installed three mini splits and tossed the oil burner. They are wonderful. Also (#2)very very quiet, and (#1) we're barely able to feel the streams of warm air. If you want to feel it, you need to hold your hand up near the unit. (#3)They are on all the time, but you'll never notice. They have a different way of operating: a standard furnace/boiler operates on "set points", so when the room temp is 4o (or whatever) below the set point, the unit comes on and heats up the space to a few degrees above the set point, using pretty hot air, then shuts offs and lets the room col down. Minisplits operate continuously near the set point, and maintain that temperature.
    (#4) in a very tight, above average insulated house the room temperatures will typically be even throughout the house, and all the surfaces as well as walls, ceilings and floors, will run at the same room temperature. (This assumes that the basement is also conditioned space.) I've used both oil and gas boilers and furnaces of many brands as well as radiant heat in several homes. IMO, you won't find a more comfortable method for heating and cooling. Plus, with a few solar panels you never have to buy fuel!

  6. Davor Radman | | #6

    My biggest fear (perhaps too strong a word, since we are discussing 1st world problems here) is zoning.
    As is mentioned in pretty much every minisplit thread :)

    I have read all those that i could find, but I'm still not smart enough.

    I don't know how many indoor units would i need. 2 compressors is enough, 1 for each floor. But indoor units..

    I will have the following rooms that need to be heated/cooled:
    1x500sqft living room+dinning+kitchen space
    1x100sqft reading/work room
    +a small bathroom on the ground floor

    1x150sqft masterbedroom + 150sqft closet (not sure if I need heating/ac here)
    2x150sqft bedrooms
    1x150sqft bathroom

    That is 8 rooms. Assumption is that doors will not be generally left opened.

    1) Do I need 8 indoor units in this case?
    2) Should i put "oversized" bathroom wall radiator instead in bathroom or possibly also electric underfloor heating?
    3) I don't think we need closet room conditioned as well, just that it is not too hot or too cold. A "leaky" door + good thermal envelope of the house could take care of that?

    So that leaves me with 6 indoor units. Prices for indor units are quite low.
    Mitsubishi MXZ-3HJ50VA + MSZ-HJ25VA + MSZ-HJ25VA + MSZ-HJ25VA Multi inverter set 3+1
    3x2.5kwh cooling / 3x3.15kwh heating is ~2000$ (sans installation). Indoor units are 300-500˘a piece. So price is not an issue.

    Does having 6 units have some hidden cons?

    I have read Are Seven Heads Better Than Three? article here, but still not sure if this is directly applicable in my case.

  7. GBA Editor
    Martin Holladay | | #7

    Davor,
    1. Unless I missed it, we still don't know your geographic location or climate zone.

    2. You haven't provided details of your building's thermal envelope.

    If you have a very tight house with very high R-values and excellent windows, you'll be very comfortable.

    Large windows in bedrooms can make things tricky. In other words, we need to know more about your house and location.

    -- Martin Holladay

  8. Jon R | | #8

    If you want a closed door room at the same temperature as the adjacent rooms, then you definitely need a head in it.

  9. Davor Radman | | #9

    Croatia, climate zone, corresponding with USA hardiness zone 7 (~NYC, Philadelphia).

    We only have some rough papers. But the house is being planned to have 8000 BTU/sq ft/year (2 times as much as a passivhaus standard). 20 cm EPS on the outside, 10 cm XPS underneeth, 20+ cm in the roof assembly. Combination of triple and some double glass windows, with mostly low SHGF. I will try to be as airtight as possible, no idea what can we aim for.

    We will have.. Moderate windows in the bedrooms. ~6x4 feet. Triple glass.
    There will be aluminum solar shades on all of the windows.

    Ductless minisplits are simply called AC (klima) here. Since we don't ever use ducts. So no need to have ductless in the name :)
    On paper, it's really great. Much cheaper to build and run. I'm just concerned about comfort :/

  10. Davor Radman | | #10

    But, as many before me, i have come in front of the insurmountable obstacle. Called wife.
    I could not imagine how strongly would she be against this idea. Comes down to.. Aesthetics. Sad.

    I'm still curious about how this system works, but it seems almost certain that we will have to go ASHP or gas + radiant. Which is OK for me, but it will obviously cost more.

  11. Randy Bunney | | #11

    Davor, I assume the aesthetics obstacle is the sight of the mini-split unit hanging on the wall. My wife and I found that we soon don't even notice the wall unit's appearance. We have 1.5 years experience living in a cold winter climate (North Central Minnesota, USA, 46 degrees north latitude) using the Fujitsu Halcyon unit in a 1,100 square foot, all electric home, passive solar home. Concrete floors, R29 walls, R56 ceiling, triple pane windows. Our project is described here: https://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/designing-hvac-system-cold-climate

    Relying upon a single mini-split to heat/cool multiple room would be uncomfortable for my wife and me: too much temperature variation in rooms without mini-split. Instead we have a unit in our great room/kitchen and bedroom. We rely upon electric baseboard to heat our small bathroom.

    Moreover each room has electric baseboard as backup and for use when winter temps drop below the Fujitsu's effective operating range (-15 degrees F below zero). We also use the smallest available Jotul wood stove as ultimate backup should be lose electrical power.

    Our only complaint on the mini-splits is that the wall units expel puffs of air cooler than room temp during the winter when the exterior compressor goes into defrost mode.

    Homeowners contemplating air source heat pump in a winter snow climate: please, place the outside condenser on a stand above expected snow level. You'll need this snow clearance for reliable operation and to keep the condenser bottom above the ice that forms when the unit goes into defrost.

    Secondly, place your unit well away from the drip line of your roof's eve to protect it from snow sliding off the roof in the winter or rain water during rainy season. The gable end of a house is often cited as a good compressor location.

    However, our air source heat pump takes advantage of being snuggled against a south facing wall which radiates heat from the winter sun.

  12. Expert Member
    Dana Dorsett | | #12

    US plant hardiness zones do not have a good correlation with U.S. Department of Energy climate zones. Historically Croatia averages something like ~2700 heating degree (Celsius) days (base 18C) per year, which would make it equivalent to US climate zone 4 (Yes, both NYC and Philadephia are in US climate zone 4A, but have colder overnight temperatures in winter than Zagreb.) (DOE zone 7 would be like northern Sweden or northern Norway.)

    Compare the temperature averages for Zagreb with those of Philadephia:

    https://weatherspark.com/averages/32017/Zagreb-County-of-Zagreb-Croatia

    https://weatherspark.com/averages/31282/Philadelphia-Pennsylvania-United-States

    Philadephia is a few degrees colder in winter, and a few degrees warmer in summer than Zagreb.

    That is a fairly temperate climate, well suited to heating with mini-splits. With 20cm of continuous EPS insulation and triple pane windows your heating loads in Croatia will be smaller than your air conditioning loads, and if they are sized for the air conditiong needs you will have more than enough capacity for heating even at your -15C/+5F extremes temperatures, way more than is needed at your roughly -10C/+14F 99.5ths percentile outside heating temperature.

    Comfort isn't an air temperature- it's all about radiant temperature. With a poorly insulated house you need the higher temperature floor or radiators to balance the cool radiant temperatures of the exterior walls and windows, which are more than 5C below the air temperature in the room when it's -10C outside. But with 20cm of EPS and triple pane windows the wall & window surface temperatures will stay within 2C of the average room temperature, and simply raising the room temperature ~1C would deliver the same or higher average radiant temperature that you would have with "normal" house heated with a radiant floor. Heating the room with the floor in a room with 20cm of EPS & triple-pane windows only requires floor temperatures a degree or so warmer than the average room temperature even at -10C outside, which is a much smaller difference than in a less-well insulated home, with very little comfort advantage over a home heated with mini-split heat pumps. With the heat pumps you would only need to raise the temperature one degree to have the same or higher comfort levels as heating it with a radiant floor.

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