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We have done what Katy suggests on 2 recent ADUs. On A third ADU we just kept the existing gas water heater and connected it to the ADU. All three have a demand operated recirculation pump. It never made any sense to put a heat pump hot water heater in an ADU...biggest ADU I've done is about 500 SF. I think I read that electric on demand are now allowed in small buildings. Katy...did I hear that from you or your guide? I forget how small the building has to be to allow that, but it might make environmental sense in many cases.

Sarah, in theory, electric tankless WH are allowed for homes ≤500 sq. ft. but as explained in the e-guide (see pg 104) this may not fly from the standpoint of the entire home meeting Title 24 energy code, since all of the compliance now needs to come from the envelope but even with great windows, slab insulation and other above-code specs, you may exceed both the heating and cooling budget and ultimately not be Title 24 compliant... (mainly since ADUs have more window area than allowed prescriptively due to how the code works.)

Sarah Deeds  Deeds Design , a bummer about using a kitchen exhaust fan is that the airflow req. are much higher—300CFM (vs for range hood: 160CFM for ADU<750 sq.ft). The Toblino that Dan shared is only .5 sones at working speed of 100CFM so this meets the noise req. even though it's 7 sones at 340CFM (see bottom of this doc: https://storage904.cdn-immedia.net/sites/default/files/elica_ss_2023_to…). From T24 compliance manual "The Energy Code requires verification that range hoods are HVI or AHAM-certified to provide at least one speed setting at which they can deliver at least 100 CFM at a noise level of 3 sones or less."

Also for microwave/hood combo check out HVI Certified Products Directory (https://www.hvi.org/hvi-certified-products-directory/section-i-complete…). 1) under Product Category filter by kitchen range hoods; 2) under Subcategory filter by microwave; then 3) click on "Model" column to consolidate ratings for the same model at different flow rates. Find models with a high setting ≥160CFM that also have a lower setting ≥100CFM that is ≤3 sone req. These ones work: IKEA 004.621.66 https://www.ikea.com/us/en/p/medelniva-over-the-range-microwave-black-s… - IKEA 204.621.65 https://www.ikea.com/us/en/p/uppseende-over-the-range-convection-microw… - other IKEA products, Blomberg, Midea, Electrolux etc. The trick I think is to find a product that has offers a lower setting around 100-120CFM; then it pretty much guaranteed will be <3 sones at that lower setting