Sizing a tankless and manifold for radiant

[urgti]

I am sure there is a formula for sizing but I have not found it either here or online. I am doing a 26x24 story and a half garage and will be doing radiant in the concrete initially and would like the option of adding a second zone upstairs later down the line.

So far from looking on here I am figuring 3 loops of 1/2 pex around 215' each run. With the second zone option how many port manifold would be best and what size heater? I left my info with a local place but they have not gotten back to me yet so I am here posting.

One reason I would like to know the heater size asap is while at Menards today I noticed they were selling off some Richmond RMTG2 series for $350 which are normally $600. They specs on the carton were 118,000 BTU and 2.5 gpm @ a 77 deg. rise. I also plan to pour the floor next weekend and would like to get my pex and manifolds in so I can pressure test them.

 

[ddawg16]

That sounds like a good price for the unit.....The BTU's sound high enough to get you where you want....the only difference is how long it takes.....

What was the rated water flow? That is the other # you need....in other words, how many gallons a min will it supply at what temp.....you can only flow so much water through your radiant heat....good chance the flow of the tankless is higher than your radiant heat....

 

[Dragster Racer]

You can always pressure test with temp fittings. The have some press on fittings that you can remove and you can convert to garden hos and a valve. That is the way I did mine. I just did one loop at a time.

 

[urgti]

Flow numbers are in original post.

2.5 gallons per minute at a 77 degree rise or about 4.2 @ 45 degrees