hot water loop off steam boiler

STEAM DOCTOR

Good morning. I am running a hot water loop off a steam boiler using the tankless coil. Do I need to mix cooler water into the loop to prevent the water from flashing to steam or is the fact that the water is pressurised and hence a higher boiling point enough to prevent the water from flashing to steam. Thanks in advance for the advice.

ChrisJ

Yes and no

The water will not boil due to the pressure,  however you are required by code to use a mixing valve in order to prevent scalding and it also allows the hot water to stay a consistent temperature.  Just think of how hot the domestic hot water can become while the boiler is making steam, 170-180F perhaps? 



You may also want to consider adding a flow regulator.  I have been thinking about adding one to my setup because if we try to get too much hot water it cools down a lot due to the volume running through the coil.

STEAM DOCTOR

hot water

I am not running domestic hot water off the loop. The loop is a heat only loop.

Mark Eatherton

Space heat or DHW???

Copper or plastic distribution?



Gots to know...



ME

ChrisJ

my mistake

Ah,  I thought when running hot water for heat you simply pull water from below the steam line.  Did not know anyone ever used a loop for that?

Mark Eatherton

Got it...

If you are running plastic for distribution, you will want to protect the tubing from higher operating temperatures. If it is copper or iron, not a problem provided you can maintain at least 5 PSI on the top of the system (.434 PSI per vertical foot above the boiler, PLUS 5 PSI).



If it were DHW, you'd have to use an antiscald mixing valve. I'd suggest using the same thing if you are dealing with plastic.



ME

jonny88

hot water zone

dans book, the golden rules of hydronic heating.page 77.you will find a piping diagram to make it easy for yourself.

Roland_18

Another choice

Roth Mini Shunt.

Greg Maxwell

Heat loop off a coil

How many BTU's are you going to put on this loop?

STEAM DOCTOR

copper

There is copper piping. The highest point on the zone is aprox 30' high so I cant come off bottom of boiler.

JStar

I would....

...at least put some form of mixing valve, either manual or automatic mixing in the loop's return water. Try to maintain 180 on the loop while the boiler is fully steamed. The worst that happens is you wind up not using the valve; and you get a little more control of the system.

wholesalerbill

hot water loop

You also need a circ pump, expansion tank, aquastat and B&G FB-38 fast fill valve, and a back flow preventor. You have to treat this loop just like you would any hot water boiler loop(zone).

wholesalerbill

hot water loop

one more thing I forgot to add, throw on a Taco SR501 single zone switching relay.

Mannu

flow chat

This is a question.



On the out part of the tankless coil, you connect a expansion tank, then circulator, then flow check valve, then pressure reducing valve?



Then the return goes back into the IN part of the tankless coil, with a flow valve?



Water supply gets tapped into the in part of the tankless coile after the flow valve?

Mannu

flow chart

i meant the title for the post above to be flow chart