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

Users who are viewing this thread


New Member
Reaction score
Ludington, MI
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


  • Screenshot_20230103_203444_SlantFin.jpg
    40.9 KB · Views: 95


Well-Known Member
Reaction score
Peace valley missouri
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.
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks