Tankless with radiant underfloor - between joists - and possible use of radiant panels - need advice

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Josh342

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Hello everyone,

I feel as if this topic has been beaten to death, based on my search, and responses from some. Here is my situation. I have a 1920's two story home in Ludington Michigan. The current natural gas furnace needs to go. I couldn't give you an idea on how old it is but I had a couple people come out for estimates and was told that I was looking at early 70's. I've own the home since 2020. I have 7 foot basement walls and the way everything is set up, along with the current ducting, it would be extremely expensive to upgrade and make the ducts sufficient. The house is a 1 bath, 4 bedroom home approximately 1500 sq ft. There are a few runs to the main floor and 1 run to the upstairs.

What I would like to do is go with an underfloor, between joist radiant setup using 1/2" PEX along with the aluminum panels. Based on my calculations, I would use 1 zone - 4 loop for main floor This would keep each loop close to the 300ft. The second floor will be tricky because unless I want to rip out the ceilings, under floor would be extremely difficult. My thoughts were to add a radiant panel either in each bedroom or one large on in an open area where the stairway comes up. I have been researching a lot and the more I read, the more confused and overwhelmed I get as to how I should approach this. I have read and watched videos of people using a tankless water heater, specifically the Takagi T-H3-DV-N. But then I read plenty of people say to avoid this because it does not have the outdoor reset. I need to do something.. I am on a tight budget and whatever I do, I want it to be acceptable.

Ideally, I would like to run the tankless with a primary/secondary setup, using a heat exchanger. I read that the tankless isn't good because it also does not get the temp high enough for the radiator panels. I was looking at supply house for those hydronic panel radiator. I go to the manufacturer docs and they give you 3 different BTU's based on 3 different water temps. The lowest BTU (for 140 degree) will work based on my heat loss calculations.

If a tankless is NOT the way to go, what would you recommend?

Any thoughts would be greatly appreciated.

Thank you
 

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Fitter30

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Any condensing boiler the return water has to be 140°f or lower for95% efficiency above 140° 87%. Floor heat to watch the floor coverings. Wood 85-87° the manufacture should have that info. A well design system runs water temp 5-10° over thermostat set point. Slant fin and others also have low temp fin tube and charts for them.
 
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