Garage in floor w/tankless heater

mikeron1

Hello, I have a tankless (takagi) water heater feeding 6-250’ loops. Wondering what the optimum flow rate (gpm) should be ? Approx 1600sf garage ..

Now I’m getting .6 gpm@120F 

thinking of adding another circulator ? 

Zman

.6 GPM should be adequate. The only reason to increase it would be if the system is heating unevenly.

I assumed .6 per loop, .6 overall is not good,

GroundUp

.6 per loop or .6 total? If the latter, this is bad. Using a tankless WH for this application is bad anyway, but they can be made to work if properly piped- which if you only have one circ, is not. Do you have a photo of the system in question?

mikeron1

mikeron1

I think it’s the same .. I’ll have to check again but it says .6 gpm on the electronic gauge on the unit and all 6 flow meters on the manifold read about 1/2 gallon a minute . Originally I had 1 circulator . I added a 3 speed on the feed and moved the single speed to return side which brought it up to 1.2 gpm .. a couple people told me I don’t need 2 circulators so I removed the 1 on return . It is a closed system w/glycol not water .

kcopp

I would add the boiler loop w/ its own circ pump... especially where you are running glycol through the system.
I know that Noritz says thats a No-No for their WH used in a similar set up.
I would also strongly recommend an air separator in the system.

GroundUp

If it's flowing .5 GPM per loop times 6 loops, that's 3 GPM through the unit. That would be okay if it were accurate, but it's doubtful. 2 pumps in series are not the same as primary secondary piping. 1 speed vs 3 speed means nothing whatsoever- there are countless sizes of each. What is the model number of the circ currently installed? 0015 maybe? What is the return temperature from the slab when the supply is 120?

mikeron1

Rite now the slab is at 53degrees return .. when I 1st turn it on .. it does have more gpm with the 0015 -3 speed vs the single speed 007 . If I let it run overnight , the return progressively comes up 

Hot_water_fan

Rite now the slab is at 53degrees return .. when I 1st turn it on .. it does have more gpm with the 0015 -3 speed vs the single speed 007 . If I let it run overnight , the return progressively comes up

Makes sense. Does it need to be set to 120? Lower should work just as well.

hot_rod

The installation manual shows a combination systems only not for heating only applications 

And no chemicals