Sunday, September 25, 2011

Tankless Water Heater for Radiant Heat

Thanks to everyone who came out to the ADU on the Build It Green tour. It was fun to be able to show off the place to so many people, and I hope that it left some of you all inspired to see more ADUs.

This post will deal with the tankless water heater and radiant heating, which I've mentioned in other posts, but never fully described.

An ADU water line splits off the water main in the main house basement, and comes to the ADU underground. Some of that (cold) water is directed to the water heater, which heats the water to ~120 degrees whenever we turn the hot water (for a shower, sink, dishwasher). The water heater is "tankless", which means that it heats up water "on demand", only when needed. A tankless, on-demand water heater is inherently is more energy efficient than a conventional 60-gallon holding tank water heater, which keeps 60 gallons of water heated constantly, even when there is no need for hot water.

Meanwhile, a heat exchange heats up more water in the heater in a separate "closed loop" to a lower heated temperature (~70-80 degrees) that runs through the Pex tubing throughout the first and second floors, providing in-floor radiant heat. Radiant in-floor, hydronic heat is the heat source, along with some passive solar heating.

There are three forms of heating: radiant, convective, and conductive heat. Most of us group these three forms together in our head as "heating", but they function totally differently from one another. 

Forced air is convective, and although it is the dominant mechanism used for residential heating in this country, it is not a good way to heat most residences. Radiant heat is generally the most comfortable and effective way to experience and manage heat. 

Radiant heats works totally differently than forced air heat.  Radiant floor heating will heat the surfaces in the house to a particular temperature (~70 degrees), and those surfaces will then radiate that heat outwards towards the occupants, reducing our body's heat loss towards those surfaces.

Radiant in-floor heating is a comfortable way to experience heat evenly throughout a home. Interestingly, with radiant surfaces everywhere, air temperature in a house can actually be lower than what you think is comfortable, and you will still feel warm. This is akin to when you're standing outside on a cold night, with your front side is facing a campfire. That's radiant heat gain working its magic on your front side, and radiant heat loss working on your back side.

Conversely, forced air heat does not heat up surfaces; it only heats the air that is then blown throughout the space, and air a poor heat conductor. That heat is quickly dissipated because air does not have the thermal mass to retain that heat. That energy that was used to heat that air is quickly dissipated and lost. The surfaces of the house will remain cool to the touch. Even if the air is warmed in a space, cold surfaces can still make you feel cold. Cooler surfaces draw heat from your body.

Houses heated by forced air tend to have spots that feel cold- areas far from the vents, or areas near cold surfaces like windows. While in the US, homes ares primarily heated using forced air (a form of convective heat), we are alone in this approach globally. Europe, for example, uses a far greater percentage of other heat types--primarily forms of radiant heat.

My water heater is a Navien condensing combi tankless water heater. It's gas powered, which is a more efficient way to heat water than heating with electricity, but both power sources are available as options for the tankless water heaters. Here's a video of the gas line from the street to the ADU, which is the gas supply that is used for both the water heater and for the gas powered cooking range.

Here's a video of the water heater. As you can see, the water heater plumbing and mechanics are a bit complicated. We'll use the radiant heating in the concrete slab on the first floor to heat the house. There are  radiant loops running through the second floor as well, but we will rarely use them. The concrete, once warmed, will easily heat the whole ADU in the winter. Once warm, it would take days for the concrete (and ADU) to cool back down. The heat demand load on this ADU will be very low, due the ADU's small size, the high R-values in the walls, ceilings, and floors, and the lack of thermal bridging. I'm looking forward to experiencing how the heat system works, and to comparing the gas bills from the ADU and the main house.


  1. Hello,

    Tankless water heaters are more and more in demand in today’s life and requirements, because of their affordability, effortless application, consistency and the majority of all the functionality to provide a never-ending stream of scorching water. Thank you...

    Bosch Cooktops

    1. very interesting post.this is my first time visit here.i found so mmany interesting stuff in your blog especially its discussion..thanks for the post! heating boiler

  2. A water heater that runs on either gas or electricity is a good idea. Personally, which energy source do you prefer to power the water heater at your home?

    Jasmin Shakespeare

  3. Thanks to everyone who came out to the ADU on the Build It Green tour. It was fun to be able to show off the place to so many people, and I hope that it left some of you all inspired to see more ADUs. plumber in walnut

  4. Great post. I don't have also an idea about the Indianapolis water heater. But when I found your blog I get interested specially in your post about tankless water heater for radiant heat. Anyway looking for more Indianapolis water heater? Check us here. Thank you so much for sharing!

  5. Great Information sharing .. I am very happy to read this article .. thanks for giving us go through info.Fantastic nice. I appreciate this post.

  6. thanks for your best post! First of all, your gas line placed correctly. And then, chimney ventilation of exhaust gases are required to follow. Asking at your state's accreditation department to find installers that specialize in Tankless Water Heater Reviews set up.

  7. Your blog provided us with valuable information to work with. Each & every tips of your post are awesome.
    Read more

  8. I’ll probably keep it short and sweet and link to this instead if thats cool. Thanks.

  9. This is indeed an informative blog about tankless water heater. This can be shared to my clients so they will be informed on what they are dealing with.

    Tankless Water Heater Richmond Hill

  10. a short time after a user's request for hot water. In regions where water conservation issues are rising in importance with rapidly expanding and urbanizing populations local water authorities offer hot water heater

  11. Easily, the article is actually the best topic on this registry related issue. I fit in with your conclusions and will eagerly look forward to your next updates. Just saying thanks will not just be sufficient, for the fantasti c lucidity in your writing. I will instantly grab your rss feed to stay informed of any updates. electric hot water heater

  12. Really Good Information to sharing the people... the concept is fantastic ..
    Universal Heating Solutions

  13. Hello,

    I'm wondering who you used to install the whole combi system for your place?

  14. Very good points you wrote here..Great stuff...I think you've made some truly interesting points.Keep up the good work.
    cartridge heaters

  15. This comment has been removed by a blog administrator.

  16. This comment has been removed by a blog administrator.

  17. This comment has been removed by a blog administrator.

  18. This comment has been removed by a blog administrator.

  19. This comment has been removed by a blog administrator.

  20. I am pretty impressed by reading your article. Thanks for sharing.

    Heating and Air Conditioning York

  21. Thanks for sharing thye article. It motivated me about water heaters.

    Heating and Cooling Scarborough


  22. This was such a great blog! I agree with the comments completely. I learned a lot about different types of AC.
    Heating and Cooling Brampton

  23. I read your post, Thanks for sharing useful information....

    Commercial Water Heater
    Marine water heater

  24. Hello, I am one of your website customers. I want to thank you for all your post and particularly this post on your website. You are doing the best job. And I wish you good luck.
    Link Building Services IndiaLink Building Services Delhi


Related Posts Plugin for WordPress, Blogger...