I’ve been lurking on the forum for a while, and am hoping to get some advice on a possible radiant system. My goal is to increase the comfort level of our house, yet try to keep things as simple as possible.
The house - we have an old 2-story brick craftsman home built in 1923 in northern Indiana. Most exterior walls have essentially no insulation, and based on my research, short of tearing out the plaster, insulating and adding a proper vapor barrier any sort of blown-in insulation is likely to cause moisture problems, especially with the brick exterior. The attic is well-insulated with blown-in cellulose (R-40+). The 30 large windows have been upgraded to double-pane, Low-E glass, etc. First floor has 9’ ceilings, second floor has 8’ ceilings. I’ve calculated a total heating load of just under 80,000 BTUs (using the tools from loadcalc.net). I used a design temp of 0 degrees F.
Our home is currently heated with a 95,000BTU 96% efficiency condensing gas furnace. The second floor stays nice and warm, but after 2 heating seasons of playing with the ductwork dampers, the first floor (especially the living room) just never feels warm - especially to my wife!
I’ve been reading for a while about under floor “staple up” hydronic radiant, and am wondering if this may be a solution for adding additional heat (at least making the floors feel warmer) on the first floor of our house. The house sits on an unfinished basement, with complete access to the joist bays. 3/4 diagonal plank subfloor with oak hardwood flooring above.
We already have a Rinnai 160,000BTU condensing high efficiency tankless water heater - while I recognize that a tankless water heater is not as recommended as a mod-con boiler, it’s installed and operating (and I'm not concerned about voiding the warranty). I’m wondering about the possibility of using the water heater, along with a Taco X-Pump Block (plate heat exchanger) to create a closed-system supplemental radiant zone under the first floor. I’d run 1/2” Pex with aluminum transfer plates in each joist bay.
- Total area where the radiant would be installed is about 700 square feet. Estimating about 3 300’ loops of 1/2" Pex assuming 2 pipes per joist bay.
- If possible I'd like to include a small fan forced hanging heater in the basement, but this isn’t absolutely necessary. This may require a second zone which likely will drive the cost of the project higher than I'd want. I am trying to keep my overall investment as minimal as possible. We live in a neighborhood where I’ll never get this back out of the house - but a happy and warmer wife is an important too!
- I would create a loop through the Rinnai and the X-Block heat exchanger, coming off this loop for our DHW with a mixing valve down to 120 on the hot water. Rinnai would likely be set to 130-140 degrees, and would target 120 degrees on the radiant side?
- If and when the Rinnai bites the dust, I’d upgrade to a proper boiler.
- Is this even a workable solution? If so, I'll work on drawing out the system for feedback and advice.
- Without breaking the bank, what other options might be better? If any?
Thanks so much for any help!