Takagi for infloor heat

[ketas47]

I am thinking about buying a Takagi Th 2 Dv tankless water heater($800). I would be using it in my 38' x 26' garage (fully isulated). I want to replace my old boiler with this water heater to use in my infloor heat system. Has anyone used this water heater for infloor systems and was wondering how well they work?

 

[jlckmj]

Since no one has answered you, I will try.
There was just a fairly extensive discussion on this subject a few weeks ago.
Try the search (along the top bar of the page) it should bring up the thread for you.

Jim

 

[ikessky]

You are going to get a mix of people saying you should never use a water heater for in-floor and people saying they've used them for years and it's great. Personally, I use a Takagi TK-JR in my 24 x 40 and had good results for my first year.

 

[BadgerBoilerMN]

Water heaters are missing outdoor reset, which increases system efficiency and comfort.

Note that most water heaters are now label "suitable" for domestic and space heating. They are generally talking about a water heater tied or close-coupled to a hot water fan coil i.e. an open system.

When you tie to a radiant floor the system should be closed, in which case a condensing boiler properly sized to the load, would be a better match. In any case, be sure the supplier provides you with a proper heat load, explains the minimum output of the unit you choose and send a drawing with system components and controls before you start.

 

[ikessky]

Badger - Does the outdoor reset work in conjunction with burner modulation to further decrease your costs? The Takagi's are modulating heaters, but it is based off the return water temp.

 

[BadgerBoilerMN]

Condensing boilers and water heaters save fuel by recovering the byproducts of combustion normally sent up the flue at 350°F or more. By condensing the flue gas in the heat exchanger, the heat is transferred to the water going to the radiation.

Low return water temperatures, typical in properly designed hydronic systems, and more easily in radiant slabs, are nearly always below the 'magic' 130°F mark where the appliance will hit 96% thermal efficiency.

Outdoor reset (ODR) insures that the supply temperature is never higher than what is necessary to maintain the inside design temperature. In my own garage the design temperature is 88° in the office and the low operating temperature in the main shop 52°F to maintain 50°F indoor temperature on the coldest days.

The Takagi, and all flame modulating burners, rely on supply and return sensors modulating and operating on both to insure minimum flow vs. output rates and in the case of tank-less water heaters a minimum return temperature. This is why we can't use tank-less on snow melting systems - even if we wanted to.

With condensing boilers, the flame will modulate to maintain design temperatures based on supply temperature and outdoor temperature inversely. The colder it gets outside, the warmer the water going to the slab. Higher efficiency and longer component life is the result.

With a tank-less water heater the flame modulates to maintain a fixed supply temperature, say 120°F. If this happens to be the design temperature for your particular radiant floor, you are all set, provided you don't mind operating the system year-round at a temperature only needed the few coldest days of the season. This by the way is how most residential boilers, water heaters and furnaces still operate today.

Properly piped, controlled and designed, a tank-less is an inexpensive way to drive a radiant slab, but less than ideal. We design many systems for folks upgrading to condensing boilers.

If you have to burn propane, condensing technology is the answer but each unit (especially on propane) should be tuned with a combustion analyser and regular maintenance never neglected.

In some areas off-peak electricity is a better option.