FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

Plate Exchanger for Radiant Heat

x_navyfc | Posted in Energy, Heating & Insulation on December 29, 2021 03:45pm

I recently installed 1/2” pex under a new cement slab in my 50+ year old home. 2 loops covering 500sqft total. 4” slab with 2”xps underneath. Climate zone 5.

 I’m trying to think of the best way to provide hot water for the slab while not taking up much space in the utility closet where my furnace and 40 gallon hot water heater is located. There isn’t much real estate available for a second HWH. Buying a tankless HWH is an option but it would be nice to utilize what I already have to keep costs down.

I’m not a fan of the idea of using potable hot water for the slab heat.

My thoughts are to use a plate exchanger to separate the hydronic system from the potable water such as:

Plate Exchanger 75 Kbtu at Menards
https://www.menards.com/main/p-1444433727819.htm

What I don’t know is if a domestic hot water heater set at under 120 degF is hot enough to transfer the heat needed to be used for in slab heat.

Is a plate exchanger 100% efficient in that an input of 115 degF will result in an output of 115 degF?

Any other ideas on what could work well?

 Thanks for your time.

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. calvin | Dec 30, 2021 06:48am | #1

    Radiant heat technology has come a long way since we built 33yrs ago. My best recommendation is to consult with a knowledgeable radiant heat designer.

    Being an older dumb carpenter who enjoys the feel of a warm floor is about how far my knowledge goes.

    We submitted our floor plan and the rest of the design, heating load and location to a company that designed and sold hose. One thing I do remember was that length of hose and layout of zones was important. Water temp going out from our boiler needed to get back to the boiler before all the heat was transferred to the slab. Of coarse on an initial calling for heat, the transfer was quick and the return temp dropped quickly……so, hose length was fairly critical.

    As the slab was brought up to set temp, the water temp drop was less drastic.

    Layout was critical to produce an even temp around the rooms. The outer wall perimeter had a narrower hose pattern than the interior layout. They also were the beginning of the runs.

    Throw in a passive solar home layout and damned if it didn’t work as hoped!

    A pretty long while ago there was a contributor here on the board that would have been a big help for you, but as times goes here so do the members. NRT Rob I think was his forum name. Might search that and peruse, you could get lucky and find some info.

    Our boiler runs at about 125-130.

    Best of luck!

    1. x_navyfc | Dec 30, 2021 06:55am | #2

      Thanks for the reply and insight. I’ll keep researching and try reaching out to those supply and design companies you mentioned.

  2. User avater
    unclemike42 | Dec 30, 2021 07:39am | #3

    https://www.supplyhouse.com/Heat-Exchangers-821000?gclid=EAIaIQobChMIucetxcOL9QIVFFNyCh0G7AmvEAAYAiAAEgL7nfD_BwE

    These folks sell a variety of hydronic heat exchangers of different sizes. each has info on hydronic floor applications, with flow rates and input and output temps.

    Included is an application guide
    https://s3.amazonaws.com/s3.supplyhouse.com/product_files/BP400-20LP-Selection-Guide.pdf

    If you operate with a lower input temperature, the heat transfer will also scale, so you would probably want to put in a larger rated exchanger than your heat load would otherwise call for.

    as you re-use your domestic hot water heater, you may want to increase the temperature setting on the water heater, and install a mixing valve to reduce the temperature for the domestic hot water.

    You will, of course, need a couple circulation pumps to make this all work, with suitable controls. You also will need an expansion tank. Probably want a pressure gauge for the hydronic loop. And faucet to let you drain the loop. And valves, lots of valves.

    Sounds like a fun project.

  3. Hydro_Tech | Jan 05, 2022 12:34pm | #4

    These guys can have lots of experience with these types of situations, I've found they are very helpful when it comes to radiant heating.

    https://www.janesradiant.com/

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Up Next

Video Shorts

Featured Story

Pros of Apprenticeship Programs

Apprenticeship programs can be a valuable tool for residential builders to recruit, train, and retain skilled employees, offering a structured pathway for career advancement and equity in the trades.

Featured Video

Video: Build a Fireplace, Brick by Brick

Watch mason Mike Mehaffey construct a traditional-style fireplace that burns well and meets current building codes.

Related Stories

  • Tools and Gear for the Moms Who Get it Done
  • An Easier Method for Mitered Head Casings
  • Beat the Heat: Cool Innovations
  • A Practical Approach to Exterior Insulation

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 81%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data