Copper tube vs. cast iron boiler

Stemmer

Good Day.
Take a look at one of the condensing boilers for your application. The Ultra fron Weil McLain should meet your clients wishes, being an aluminum block with water content and will run at low temperature thus no special externial controls, mixing vavles etc. to worry about.
Stemmer

Chuck_7

Copper tube vs. cast iron boiler - What do you think
(Smaller size boilers)
Generally I spec. copper tube because of the speed of response goes along with the contol we usually use.
A client of ours prefers cast iron based on maintenance.?
Now (for this client) I need to spec. a boiler for heat-add to a water source heat pump loop. Tough for me to look at cast iron with the low temp. water (even though I am designing it with secondary pumping with a high proportion of bypass).
Any thoughts?

For extra credit - On water source heat pump projects I design the boiler secondary pump with enough bypass to maintain a high temp. return to the boiler. This is fine for a running system but in practice the boiler will still see low temps when the pump and boiler cycle on. Is there a problem with this???????????

Steve Ebels

Use a Cast Iron

Boiler with pump logic built into the control, I.E, Buderus or Viessmann. This keeps the pump from running until the water is at a preset temp. Low water temps (<140*) are no problem for either of these brands.

hot_rod

Regardless of cast or copper

you need to be concerned with condensation in the hx and flue pipe. Extended run periods below the fuel dewpoint will cause this, regardless of copper or cast iron construction.

Condensing boilers excepted, of course. These will have aluminum or stainless HX's that are designed to run, happily, below condensing temperatures. We hope!

Copper or cast? Depends on the application. I find the higher mass, larger water content cast best for multi zone, possibly micro load zones, common with todays zoned systems. Less cycling, provided by BTU's stored in the water itself and the mass of iron.

I like the copper for steady consistant loads. Snowmelt, dhw production, maybe connected to a matched air handler, stuff like that.

I'm not convinced copper tube boiler can handle 110 return temperatures continually, as some say, and I have a barn full of 5- 12 year old ones to prove this therory.

Raypak includes a bypass tube and ball valve to handle low return temperatures, to a point. It does not provide boiler protection under all conditions, however.

hot rod