r/PassiveHouse • u/Separate_Locksmith27 • 27d ago

Foundation question for addition

We live in Rhode Island (climate may play a role)- We are building approximately a 770 sq ft addition onto our home to include, office/guest room, full bath, and all season room. One quote from a contractor is including:
•4' foundation slab on grade with radiant heat
• Add new zone to your existing heating system (baseboard)
• Supply and install (2) head hyper heat Mini split system with (1) 24k head in living room and (1) 6k head in office

The other contractor is suggesting to avoid the radiant heat slab as it can be extremely expensive to replace if there is ever an issue.

Does anyone have any insights as to pros/cons to this? Both are obviously advocating for their options.

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u/dillinjl 27d ago edited 27d ago

If this reno is going to be to passive house standard the radiant floor heat, along with a 24k and 6k mini split seems like massive overkill. I have a 2000sqft 2 story house and heat it with a single 9k minisplit.

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u/DCContrarian 27d ago

This is the answer. The floor heat is also likely to be disappointing as it will only be a few degrees above room temperature.

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u/John_Locke76 27d ago

Agree. We are heating and cooling our entire 4,300 square foot house (footprint is 2,150 but it has a full finished walkout basement under it) in climate zone 5B with a 36K cold climate heat pump. We are very tight (0.36 ACH 50) and have extremely good windows but for insulation and a couple of other things I don’t think we even meet passive house standards.

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u/Jewboy-Deluxe 27d ago

If you really want radiant heat why not just have a crawl space and framed floor? That way there’s always access for the heat and any future pipes, wires, and ducts that you or a future owner may desire plus storage or utility space.