Modifying Takagi Jr to handle radiant heat

DD_5

I'm looking at a Takagi Jr, NG unit that is now providing radiant heat for baseboard rads. The problem is it's efficiency, lack of it, because as long as there is a call for heat from either of the two t-stats the circ pump sends flow through the Takagi (and then through a two way zone valve) and as long as there is flow through the unit the burner is firing and the flue fan is on.

I'd like to add a high/low limit that switches the takagi  off but allows the pump to run as long as the t-stat calls for heat. This would include a 20 degree delta T, switching the Takagi back on once the temp in the primary loop drops to the lower temp. I'm thinking creating a cycle will lower the gas bills and electrical. Anybody have ideas of a good way to do this if this is the way to go? I'm thinking Honeywell aquastat...

CMadatMe

Hate to Say

But it is what it is. Your way out is a storage/buffer tank. Have the water heater supply the tank and draw from the tank for the radiant. You then could use a aquastat to turn on a pump when the tank needs to be satisfied. Funny thing is by the time you add up all the extra cost ontop of the orginal cost of the Takagi you probably could have purchased a mod/con boiler that is made to do the job. 

DD_5

Squeeze a nickel

spend a dollar....Thanks. A buffer tank it is.

DD_5

Flat plate heat exchanger instead of buffer tank

Would the right pump control combined with a flat plate HE (or a Taco x block) work at all or do I have to have the thermal mass of a buffer tank? I could set the delta T between the system side and the heater side so that the heater pump cycles instead of running continuously...It looks like the X block handles this easily but again, do I just have to have that thermal mass? 

joel_19

buffer

Heat exchanger adds no mass will gain you virtually nothing. Buffer is the way to go if you really want a water heater doing a boilers job.

Gordy

Funny

Instantaneous water heater+Buffer tank= Tanked water heater, for cheaper



Not that I care for either  to do a boilers job unless the load is real small.



Gordy

CMadatMe

Funny

Gordy you make a great comparision. Your absolutely correct. You just made a water heater. I just posted on another thread about how I dislike water heaters for radiant unless a very small load. Happy new year.

Gordy

The point

 Being some people think they are saving big money with a tankless as a boiler. When in the end with the necessary modifications they end up being the same cost, and less efficient. Or a tanked water heater they could have spent way less money on.





 Happy new year !!          Gordy