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Is there any way around putting a heat source in every bedroom?

Alyssa Hoyt | Posted in Building Code Questions on

I was speaking with an HVAC guy in my area today who reminded me that code says we have to have a heat source in every bedroom. We’re planning on putting a single head ductless minisplit in our 1450 sf high performance home (to be built next year). Are there other exceptions/solutions out there, or do I just stick a Cadet heater in every bedroom and disconnect them after the inspector checks it off his list?

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Replies

  1. Brian P | | #1

    It would be worth speaking to the local building inspector; explain your house plans and ask if they'll sign off on the single mini-split.

    Regardless of their answer, you could just put an extra 120v outlet in each bedroom, in a location where a small wall mount electric heater makes sense (look at the clearance specs for the heaters). Convectair makes nice 120v plug in units:
    https://www.convectair.ca/us/products/120v-plugin/apero

    The extra 120v outlets are easy and then worst case, you have to buy a couple heaters...which maybe you'll find useful at some point.

  2. User avater
    Dana Dorsett | | #2

    The IRC does not require a heat source in every bedroom. The requirement is that all finished rooms be capable of being heated to a minimum of 68F or more at the 99% outside design temp with the door closed. Your local code may vary, and it's important to know the letter of the local code before proceeding.

    In a high-R house that is often possible to achieve 68F in all rooms by bumping up the setpoint of the mini-split in the common area a few degrees. Some locations have a 78F maximum requirement for habitable rooms, which puts bounds on just how high you would be allowed to crank it up.

    This requires a bit of analysis, starting with the 99% heat load of the room. You're allowed to subtract 230 BTU/hr off that load number for a single occupant. Then it's a matter of calculating the temperature drop across the partition walls from the common area to that bedroom with that much heat loss.

    For a first-cut crude approximation, assume an uninsulated partition wall is good for about R4 or 0.25 BTU/hr per square foot per degree difference. So for example, if you have a bedroom heat load calculated at 800 BTU/hr, less 230 BTU/hr for the occupant leaves 570 BTU/hr. If you have 150 square feet of partition wall & door between the bedroom and the fully heated space that' 570/150= 3.8 BTU/hr per square foot. that has to move through the wall. At U0.25 that would mean a temperature difference of 3.8/0.25= 15F, which means you'd have to heat the common area to 83F, which isn't realistic, and would exceed the 78F limit in locations with that restriction.

    But if the heat load calc for the room comes in at 450 BTU/hr before occupants, subtracting out 230 BTU/hr from the load leaves 220 BTU/hr that needs to be supplied through the wall, or 220/150' = 1.5 BTU/hr per square foot, at U0.25 that means the heated common space only needs to be 1.5/0.25 = 6F warmer. That means you only need it to be 74F in the common area to keep the room at 68F, which IS a credible number to assert.

    You can fine-tune it based on the actual U-factor of the door- usually less than R2, which helps, and some partition walls may only come in at ~R3 depending on construction details which also helps. A ventilation scheme that supplies bedroom ventilation with warm air from the common space helps a little, but really not very much at low cfm volumes and low delta-Ts.

    If it doesn't pencil out to under a 10F delta, in a 1450' home it's also possible to get there with a ducted mini-split solution, if you plan ahead of time where the mini-duct cassette and ducts can be accommodated fully within the pressure and insulation boundary of the house.

  3. User avater
    Dana Dorsett | | #3

    From the IRC:

    http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_3_sec003.htm

    "R303.9 Required heating.
    When the winter design temperature in Table R301.2(1) is below 60°F (16°C), every dwelling unit shall be provided with heating facilities capable of maintaining a minimum room temperature of 68°F (20°C) at a point 3 feet (914 mm) above the floor and 2 feet (610 mm) from exterior walls in all habitable rooms at the design temperature. The installation of one or more portable space heaters shall not be used to achieve compliance with this section."

    That can be met without a heat emitter in every room in many or even most high-R houses. So it really depends on what you mean by " ...high performance home...", and what the actual heat loads are.

  4. Alyssa Hoyt | | #4

    Dana, thanks for your insightful responses. I'll check with the county and see if I can convince them that we don't need the extra heat sources. The county I'm in is pretty conservative that way, but we're also close to Portland, OR, so maybe I can point to some good examples there. The bedrooms would be upstairs, so I don't think it would even be necessary to overheat the main living area too much to make it meet code upstairs.

  5. tylerbradshaw | | #5

    All good answers and suggestions on how to easily meet this requirement with something other than 1 heater per space but in my experience, mostly in California, the code does not require 68F in all "finished spaces" as suggested above. Our California Building Code and Residential Building Code both require 68F for "Habitable Spaces". in the RBC, they clearly define a Habitable Space as "A space in a building for living, sleeping, eating or cooking. Bathrooms, toilet rooms, closets, halls, storage or utility spaces or similar areas are not considered habitable spaces." This is particularly important when you try to apply this to commercial spaces where its very common to have finished spaces not conditioned at all, even on exteriors where its known they are unlikely to exceed 68F during winter. Also in California, we have some cities with their own amendment language requiring 70F such as San Francisco and Berkeley.

  6. User avater
    Dana Dorsett | | #6

    Tyler: Thanks for clarifying the code language distinction between "finished" vs. "habitable" spaces!

  7. Kenneth Gartner | | #7

    Alyssa, we have this same situation. We plan to use minisplits as our primary heat. In our case, we are not doing any dramatic 'ducting' to ensure the minisplit heating reaches distant rooms in a timely fashion.

    We will install an inexpensive hard-wired 240v Cadet (under $100 from amazon) in the baths and the bedrooms to satisfy the powers-that-be. If you are under a code regime, the irc is clear that plugin space heaters do not count. Although I hope to have them set to 'off' most of the time, I can see the value of keeping them as they provide individual room control (you might want to warm it higher for a massage or if someone is ill) and offer a backup in case minisplit is out or suffers polar vortex anemia.

  8. JAMES KREYLING | | #8

    Cheaper and quieter than a fan-powered Cadet heater to fulfill code compliance, would be to hardwire in a basic electric baseboard on a thermostat. Easy to leave turned "off." In the bathroom, a Panasonic WhisperWarm exhaust fan/ heater combo gives a great solution to both the ventilation requirements and heat when you need it. Put both functions on time switches and they will only run for as long as you need them, even if you forget to turn them off. A Defiant 30469 from Home Depot gives you a choice of time settings and handles the load of the heater. Keeping it simple but comfortable.

  9. Jon R | | #9

    I wouldn't count on the occupant as a "heating facility" - a previously unoccupied closed door room is going to remain too cold for hours.

    Just install baseboard electric heat where the inspector wants it.

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