Subject: Re: Steam and hot (hydronic) water from same boiler?

From: [email-masked] (DWinstonPE)
Date: 20 Oct 1995 03:29:43 -0400

In article <[email-masked]>, [email-masked] (Christopher
Owens) writes:

>I want to pull a hot water loop off a steam boiler, for the purpose of
>heating an indirect domestic hot water tank (and maybe for supplying a
>basement hot water radiator or baseboard while I'm at it.)  I believe
>this should work in theory, but my plumber is a bit skeptical.  I
>respect skepticism in someone who installs expensive, durable stuff in
>small spaces, so I'd like to hear from anyone else who's done what I'm
>proposing.

It is generally considered poor practice to take water from a steam boiler
for any purpose other than blowdown. If the tappings you mention are close
to the water line, you could wind up pulling steam into your circulating
pump, and killing the bearings, seals, motor, etc.
The Slant Fin Galaxy series boilers are availible with tankless coils.
Best to use the right equipment for the job rather than create a one-off
kluge such as you are proposing.

Don Winston PE <[email-masked]>
Mechanical Solutions
Great Neck, NY

---

From: [email-masked] (burdickw)
Date: 20 Oct 1995 22:46:28 GMT

Christopher Owens ([email-masked]) wrote:
: I want to pull a hot water loop off a steam boiler, for the purpose of
: heating an indirect domestic hot water tank (and maybe for supplying a
: basement hot water radiator or baseboard while I'm at it.)  I believe
: this should work in theory, but my plumber is a bit skeptical.  I
: respect skepticism in someone who installs expensive, durable stuff in
: small spaces, so I'd like to hear from anyone else who's done what I'm
: proposing.

: Both Burnham and Superstor (a maker of indirect hot water heaters) say
: this should work fine, the only caveat being that boiler water in a
: steam system will be dirtier and more highly oxygenated than boiler
: water in a hydronic hot water system, so that we should use high-grade
: stuff like a bronze 3-piece circulator instead of a cartridge unit.

: As long as I'm running this hot water plumbing around, I'm thinking of
: adding a radiator or a baseboard in the basement, which would have a
: separate circulator.  I'm completely mystified about how to size the
: basement radiator (since it'll be carrying 215 degree water), and
: about how much extra capacity to size into the boiler to cover the
: indirect heater and the basement radiator.

: Anyone done any of this?

Chris--

I haven't done this, but I do have some thoughts based on other
experiences: 

1) Taking a hot water loop off the water in a steam boiler for use below 
the water line is a standard solution...has been done for years in 
steam-heated buildings where a basement is converted into useable space.  
The advice re dirtier, more corrosive water and high-quality components 
is sound.

2) There's no reason why you shouldn't run an indirect water heater off
it, either.  For years, steam boilers were installed this way before
modern "tankless" coils were invented.  The difference today is that they
use circulators or zone valves to control flow (thus temperature) and
usually the heating coil is enclosed in the storage tank.  In the old
days, it was gravity convection, no thermostatic control and separate
"side-arm" heaters! 

3) The indirect water heater manufacturer's literature will tell you how 
much boiler capacity to allow.

4) The load on the boiler from the basement radiator can be calculated by 
your plumber or any competent heating contractor or mechanical engineer.  
The 215 degree water is the same temperature as the steam, so the 
equivalent "square feet of radiation" is just the same as the other 
radiators in your house!  (1 SQ FT equivalent direct radiation, or EDR, 
gives off 240 btu when heated with 215 degree steam and mounted in a 70 
degree room).  Add 20% or so for piping and pickup factors to get the net 
boiler load.

If you're using an old radiator, see the ASHRAE Handbook on equipment for 
the calculations.  If you're using new baseboard or a convector, see the 
radiator manufacturer's instructions.

The more difficult question is "how big should the radiator be to heat 
the basement"?  Again, a competent heating contractor or engineer can 
answer this based on the conditions in the house.  Or you might look at 
the ASHRAE books and take a stab at it yourself, just for fun, but it would 
be a great deal simpler to get somebody who is familiar with the 
calculations to look at the job!

				--Bill Burdick