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Community and Q&A

Best Type of Back-Up Heat

CRC1 | Posted in Energy Efficiency and Durability on

New construction.  We are doing mini splits.  We are being required to install additional heat sources in each and every bedroom and bathroom for “backup”.

Double stud walls.  Raised heel trusses.  Aiming for tighter than average envelope with blower testing, correction, and retesting.

The HVAC contractors are planning cadets for each room.   Our contractor has offered electric resistance heat in the bathroom floor which we really want to only use on demand.  Will they take too long to be usable?  Would radiant panels provide more immediate infrared?  How long do cadet type heaters take to warm?

The bathrooms will be used for 20-25 minutes each morning and night.  I don’t want to run these things for hours.   The bedrooms heaters may not ever be used.   We set our night time temps very low and prefer blankets over whole house heating for sleeping hours, much more pleasant.

https://www.homedepot.com/b/Heating-Venting-Cooling-Heaters-Wall-Heaters/Cadet/N-5yc1vZc4k3Zbd?storeSelection=

Ceiling radiant?

In floor electric resistance?

Are these reasonable?

Regards,

Carl

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Replies

  1. Walter Ahlgrim | | #1

    If you want a bath heater that will make you feel warm quickly I would look a inferred heaters.

    https://www.amazon.com/Heat-Storm-Tradesman-Outdoor-Infrared/dp/B00667DVB6/ref=sr_1_5?crid=2ATGT7XZBFSWE&dchild=1&keywords=infrared+heater+wall+mount&qid=1627168156&s=home-garden&sprefix=infrared+heater+wall%2Cgarden%2C210&sr=1-5

    My guess is it is one of those ideas that sound like you will use a lot but never gets used

    The old school way is a retardant ceiling heating wire applied to the drywall and hidden in a textured finish and very unobtrusive to my eye but even lights texture is out of fashion today.

    https://www.greenbuildingadvisor.com/question/backup-heat-for-mini-splits-electric-cove-heaters

    Walta

  2. Expert Member
    Peter Engle | | #2

    Who is "requiring" you to install backup heaters, and why? If it is a local jurisdiction and you are confident that you won't need it, I would go with the cheapest solution and even consider removing it once the house is finished. That would probably be electric baseboard. The Cadets would also be a potential solution, as they take up little space in the room and are not very expensive. Any radiant panel solution is going to be slower and more costly than either of these solutions. As Walter says, Infrared heaters are probably the fastest.

    If, OTOH, it is a comfort question from a family member or significant other, the calculus changes. I prefer in-floor electric heating for bathrooms, as it does take the chill out of the air and make the room more comfortable. It is not fast, however. Typically, you would have it on a timer so that the floors are warm when you get out of bed in the morning and then they shut off for the remainder of the day. I would doubt that radiant floor, wall or ceiling would be the best solution for the bedrooms based on your information above. None are fast-reacting, but all could comfortably and quietly add heat to the room if the central system is having trouble keeping up. All are more expensive than the alternatives.

  3. Expert Member
    Malcolm Taylor | | #3

    Carl,

    I'd be temped to instal something like this that can be easily removed - or on the off chance you did need back-up heat, put back in. https://www.convectair.ca/en/products/120v-plugin/apero

  4. Roger Berry | | #4

    CRC1,

    I have done heated tile, infra-red lights and radiant heaters in assorted prior homes. While the feel of a warm tile floor is nice, they do take a long preheat. I had two thermostat failures and two sensor failures in the space of two years....so heed the advice of others on this site that recommend embedding at least three floor sensors and pray for better QC than I got on my thermostats. It should be noted that a warm tile floor does not have any significant effect on air temperatures, which I have found to be far more important. A bath mat keeps my feet warm enough.

    The radiant cove heaters in my current bathroom do just fine at keeping the room's ambient temperature at 70F, but I do not rely on them for bath-time comfort. The air is essentially ignored by far infra-red radiant, so the air gains its heat via conductive transfer from the heated objects in the room. (walls, etc.) The more aggressive near infra-red sources like you see for patio dining will definitely throw enough warmth to feel quickly, but your distance from the source is critical. And the side of you away from the heat source will not be warmed. Another downside is that anything very close to the source is at real risk of igniting. The lighting effect also makes you feel like you are in a toaster oven.

    The electric baseboard heaters will warm the air in the room, albeit a bit slowly. Convective flow can only move air just so fast. You would likely need a very extended run time to push up the air temperature high enough for comfort.

    I generally do not bathe with my clothes on, so stepping out of the shower into 70F air feels very chilling. Prior attempts to use heater bulbs in overhead fan/heater units mostly resulted in my bald spot getting cooked, the rest of me remaining chilled.

    I have found the simplest and cheapest answer to be a small fan-heater that sits on the floor or edge of the counter. Ten minutes before a shower, I put it on mid level heat and let it run until I am finished toweling off. No chills. The regular bath fan then goes on to dump the excessive humidity outside. The only significant downside is how much lint collects in the newer heater types that have very fine fins. I have an old school fan-heater that is easily blown clear.

    While there are inset wall heaters widely available, I don't recommend them for two good reasons. They consume wall space generally needed for towel bar placement and the risk of hanging something in front of them that will burn is too high for my taste. I have removed them for others after near disasters with towels and robes catching fire. They also suck up lint and are much harder to de-lint. Some do come with filters...another maintenance item.

    For the other locations you have mentioned, I would push for cove heaters over ceiling radiant or baseboard. Very cost effective and much less constraining on how you do the ceiling. I grew up with early radiant ceiling panels, which required very stout mounting and resulted in a suspended ceiling appearance. The panel placement was very dominant, which might be a bad thing if in the future someone attempts to put up a hanger. The embedded wire varieties and others remain at risk for damage from ill informed hook placements.

    As I have said in other threads, I wish we had put in mini's, but a variety of constraints led us to the cove heaters. No hair problems, no furniture placement restrictions, no noise. Like wall paper they have become invisible to us. My next design will have mini's and cove for back up. Even if resistance heating is expensive, they make a nice back up to a dead mini or the random -25 winter day.

  5. CRC1 | | #5

    "Who is "requiring" you to install backup heaters, and why? If it is a local jurisdiction and you are confident that you won't need it, I would go with the cheapest solution and even consider removing it once the house is finished. That would probably be electric baseboard. The Cadets would also be a potential solution..."

    Good question and one I have asked my GC more than once. I may have to chase it down myself. Suffice to say that the minute you say you intend to use a mini split system and refuse to install forced air/central air with all the associated ducting shenanigans contractors start to look at you like you are from outer space. "We can't recommend that! Etc." This in a hopefully well insulated/air sealed home in a dry climate that rarely goes below 10F or above 100F.

    "I'd be temped to install something like this that can be easily removed - or on the off chance you did need back-up heat, put back in. https://www.convectair.ca/en/products/120v-plugin/apero"

    That's a nice enough looking unit and would not require wiring and drywall work. And mobile as well. Have you used them?

    "I have found the simplest and cheapest answer to be a small fan-heater that sits on the floor..."

    Is that what the Convectair unit is?

    1. Expert Member
      Malcolm Taylor | | #7

      CRC1,

      I haven't used the Apero, but it seems like a good solution for rooms that may need a small boost for several months without taking up space the rest of the year. Closer to a portable heater, but should be accepted as a permanent heat source the way a small floor fan-heater may not.

  6. Roger Berry | | #6

    CRC1,

    I checked out the Apero by Convectair and my best understanding is that it is essentially a large plate of aluminum with heating wires embedded in it. The heat flow is by convection like the company names implies. The main advantage to such types of wall mounted heaters is the relatively lower temperature of the heated plate and greatly expanded contact area. It would be hard to ignite towels or clothing items with this format. It will also be slow to warm the air. I think the idea that the louvers will direct heat to the center of the room fails Martin's magic arrows test.

    Convectair has a line of forced air heaters, (Soprano, Piccolo, etc) just use the link and scroll down to see links for other product types. The high mounting position of the Soprano might easy the lint accumulation problems I have with my floor based unit. The Piccolo is wall mounted between the studs much like many wall heaters. The heater element appears to be single rod like the ones found in toaster ovens. Far less of a lint catcher than the coiled wire element in mine.

    The newer offerings for small bath heaters by Lasko and others provide safer use in tight quarters by using either ceramic elements or hybrids that have the appearance of numerous small fins. The idea is to prevent very hot elements creating fire or burn risk. They do tend to clog up pretty quickly.

    You can find ceiling mounted heaters from Broan and others that use a fan to pass air over heating elements which does save the wall space for towel bars and robe hooks. I keep my fan heater on the floor because we don't have any cabinets in the shower half of the bath.

    You mentioned being in a dry environment, which sounds like our semi arid environment. The one thing I have learned about very low humidity air is one flash dries if stepping out of the shower. The effect is greatly enhanced by very high ceilings. My comfort work around is to keep the shower in effectively its own room and to warm the air fast with the heater fan. The combination of higher humidity provided by the shower and the rapid heat of the fan makes bathing less chilling.

    The air temperature can go up to 78-80 pretty quickly, which sounds nuts but works out. The convection type of heaters will simply take much longer to warm the total volume of air. Think of them as being like a lazy river and the fan being a rushing rapids. I have two wall mounted convection type heaters that are best for placement in a bedroom where slow even heat is more appropriate. And I do emphasize slow.

  7. Expert Member
    Zephyr7 | | #8

    I'll add the "who is "requiring" this "backup" heat? I've heard of this kind of thing being required by insurance companies before by people who heat their home with wood. In that case, backup heat makes sense since wood boilers and wood stoves require a person to load them with the wood "fuel", so they can't operate automatically entirely unattended. The insurance companies don't want a freeze risk, so they require a "conventional" heat source such as electric, natural gas, propane, etc. They just want something that can work entirely unattanded in case you're away.

    Heat pumps are an established technology! They've been around for a looong time now (decades), and they can operate completely automatically and unattended with no need for user intervention. Many already have electric resistance "auxillary" (backup) heat in case it ever gets too cold outside for them to work.

    I don't see why anyone, municipality or insurance company, would require "backup" heat for a heat pump system. If either of those two types of entities is the one doing the requiring, then I'd install whatever is the absolute cheapest thing that passes muster and isn't too intrusive in the rooms. This might mean electric resistance baseboards, or it might mean some kind of radiant or in-wall electric resistance setup. Efficiency doesn't really matter, because it'll never be running anyway -- YOU know your HEAT PUMP is going to be doing all the work after all.

    I'd first try making the argument with the one doing the requiring that your mini splits are heat pumps, an established technology, and you don't have need of a backup system. If the one doing the requiring is a spouse, then, well.... You'll have to find something that satisifies said spouse.

    Bill

    1. Paul Wiedefeld | | #10

      In my experience it was the bank. However, it had nothing to do with the heat pump (it was a furnace at the time). Their concern was that without a permanent heat source in every room, an occupant would use a portable space heater that might cause a fire in the house they own.

  8. CRC1 | | #9

    "You mentioned being in a dry environment, which sounds like our semi arid environment. The one thing I have learned about very low humidity air is one flash dries if stepping out of the shower. The effect is greatly enhanced by very high ceilings. My comfort work around is to keep the shower in effectively its own room and to warm the air fast with the heater fan. The combination of higher humidity provided by the shower and the rapid heat of the fan makes bathing less chilling.

    The air temperature can go up to 78-80 pretty quickly, which sounds nuts but works out. The convection type of heaters will simply take much longer to warm the total volume of air. Think of them as being like a lazy river and the fan being a rushing rapids. I have two wall mounted convection type heaters that are best for placement in a bedroom where slow even heat is more appropriate. And I do emphasize slow."

    Good insight. Thank you. Fan heater in the bathroom. Slower more continuous convection heaters in the bedrooms, possibly removeable as we may never use them.

    "I'd first try making the argument with the one doing the requiring that your mini splits are heat pumps, an established technology, and you don't have need of a backup system. If the one doing the requiring is a spouse, then, well.... You'll have to find something that satisifies said spouse."

    Ha ha. Yes, I definitely need a comfortable spouse. My neck is on the block on this one and I think it will work out but all you have to do is look around to find that no one has exact solutions.

    Meanwhile, on further questioning our GC the code here states something to the effect that the house must be "adequately heated" giving the HVAC guys free rein to require lots of heat sources in lots of places before they will sign off on the install. Remember, these are the same guys who want to install forced air systems for guaranteed comfort and, in addition, get directly incentivized to increase cost which translates into their own personal wallet comfort. They hold us captive to their designs unless we, as homeowners, pull our own mechanical permit and perform the entire install ourselves. Catch two is that they are also tapped as our electrical contractor and it is not clear they would even cooperate with running the legs to our mini splits if we do the installs ourselves...

  9. Paul Wiedefeld | | #11

    CRC1, how many minisplit indoor heads are you thinking?

    1. Expert Member
      Dana Dorsett | | #12

      My question exactly!

      With double studwalls and raise heel trusses for way better than code-R the heating loads for individual rooms are going to be pretty small- TOO small to run wall-coil type mini-split heads efficiently & comfortably.

      Electric baseboards or cove heaters SIZED FOR THE CALCULATED MANUAL-J HEAT LOADS of those rooms isn't a terrible idea, even though it's mostly unnecessary expense in a high-R/low-load house. Oversizing a baseboard or cove heater isn't terrible for efficiency, but it's not great on user-comfort when they are actually needed. Like any space heating problem it's best bend over backwards to avoid oversizing the heaters you want it to be comfortable, even with intermittent use.

      1. Paul Wiedefeld | | #13

        Exactly - if it’s a head per floor there’s a discussion. If it’s a head per room, it’s a waste

  10. CRC1 | | #14

    "Heat pumps are an established technology! They've been around for a looong time now (decades), and they can operate completely automatically and unattended with no need for user intervention.

    I don't see why anyone, municipality or insurance company, would require "backup" heat for a heat pump system. If either of those two types of entities is the one doing the requiring, then I'd install whatever is the absolute cheapest thing that passes muster and isn't too intrusive in the rooms. "

    Yes, it has been revisited and the GC claims "adequate heating" is required by code here in Hood River Oregon. The upshot is a strong recommendation to embed "Cadet" heaters and pay for drywall holes on 240v legs in bedrooms with two units in some common spaces... GRRR.
    They are not willing to accept anything that is not hardwired.

    1. Expert Member
      Zephyr7 | | #15

      If this is your GC’s interpretation, it might be worth double checking with the city. Maybe your GC just doesn’t like heat pumps. If the city requires “hardwired” equipment, a heat pump should still satisfy the rules since heat pumps are hardwired and permanently installed too. Maybe a visit to the city with spec sheets for the heat pump in hand to show that the unit is rated to ha doe the full heating load of your structure down to the usual cold temperatures that can be expected in your area would get you an OK here.

      Bill

  11. Jon R | | #16

    IRC 303.10 requires 68F with non-portable equipment and presumably closed doors. Hard to meet that in bedroom/bath/office with only non-ducted mini-splits.

    If you intend open doors and don't mind colder, then "backup" is a reasonable description for the required heaters. I like the bathroom warmer.

    Bathroom infrared bulbs are very fast (no timer or pre-warming needed) and work OK if there are several at different angles. Other types of bathroom heat are likely to get left on all the time, providing more than 100% of that room's load (making "supplemental" a misleading term).

    1. Keith Gustafson | | #18

      yup, while we may know a superinsulated house will not see cold temps in almost any conditions, the room would count as unheated per code. I had to put a wall mount fan heater in the bath of my last house, and the building inspector was right! I loved that little heater you could dial up to blow on you while on the pot in the middle of the night.
      If you are pre sheetrock, a few electric baseboards or fan units will be super cheap, and hell, if 10 years from now your heat pump dies, you won't be overpaying for a rush fix

  12. Trevor Lambert | | #17

    My house is similar to yours. A mini split on each floor. We went with cove heaters in the bedrooms. Also have some on the main floor, enough to cover the entire heating load of the house. This already paid for itself when the main floor mini split stopped working in the dead of winter and the HVAC company took weeks to figure out the problem (they wired it up wrong; so much for "pro advantage", eh?).

    No regrets with the decision. The bedroom heaters are on a thermostat, but barely come on. The main floor, aside from that one emergency incident, never needs back up heat. We have no supplemental heat in the main floor bathroom, and don't miss it. It's a couple of degrees cooler in there on the worst nights, but it's just a two-piece bathroom. We have infloor heat in the upstairs 4-piece bathroom, and I'd recommend that as well. Set it on a timer for when you're often bathing/showering.

    I think the key to making this setup work is passive house levels of insulation and air sealing. We're in zone 6, insulation is 48/56/116, with 0.2ACH50 leakage.

    Having said all that, I'd still strongly recommend a ducted mini split for the bedrooms. The cove heaters are fine for winter, but summer is another story. We're getting by with leaving the bedroom doors open as much as possible, but it would be nice not to have to worry about that. In fact, I did install a slim duct mini split upstairs, I just haven't gotten around to retrofitting ducts. I wish I'd thought of that in advance.

  13. CRC1 | | #19

    Keeping doors open in a tight house seems like a good idea anyway given the improved air quality. Are you saying you the cadet heaters are not turning on much, or not at all?

    I like the near instantaneous potential of a heater fan since it can be used at random times, a heated floor can't do that.

    Meanwhile the calculated heat load sheet from the HVAC installer lists default values for air sealing and insulation, "average" or whatever, and includes some consideration for "ducts" that we would not have so with that in mind I have no idea how much oversizing to assume in their results. The heat load is @36,000 Btuh by their Man J. With other fudge factors they likely included I'm wondering how much they are over estimating. 10 or 20 % would not surprise me but I'm no expert.

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