I am looking at the ICC Intl Mechanical Code, in section 309.1

309.1 Space-heating systems. Interior spaces intended for human occupancy shall be provided with active or passive space-heating systems capable of maintaining an indoor temperature of not less than 68°F (20°C) at a point 3 feet (914 mm) above floor on the design heating day. The installation of portable space heaters shall not be used to achieve compliance with this section.

I am wondering what this means. e.g., capable if you set the thermostat on 80 and it gets up to 68 in that room?

Let's say you have some cold rooms in a house. Most of the house - you set the thermostat at 70, those rooms are about 70 - but in some rooms is struggles to get over 65. Is that a code problem or it is okay because you could turn the heat up to 80 and then that room would be able to get over 68?

Also what exactly does it mean to "maintain" the temperature? e.g., you get it to 68 but it cools off very quickly by a few degrees within an hour?

How is this part of code actually applied?

  • Basically, if you're a landlord this is your problem. If you're a tenant, this is how you make it their problem.
    – Mazura
    Commented Nov 16, 2019 at 21:53

1 Answer 1


Just because it isn't tweaked right doesn't mean the system is not "capable of maintaining..."

afaik, it's applied when someone complains. Which they have the right to if the system cannot maintain a temp above 68, measured 3' off the floor.

If it runs 24/7 and drops below 68 "on the design heating day" (w/e that means) then it does not meet code. If it has to be set at 90 to get 68, and it runs less than 24/7, never dropping below 68, then it meets code.

-"maintain", literally. If 90 is as high as the thermostat will go, and that can't keep it above 68, then it can't maintain. The system is either undersized, needs to be balanced, or can't deal with the heat loss.

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