Copper fin vs cast iron boiler, any opinion?

Alex Ma

Copper fin vs cas iron boiler, the advantage/disadvantage, any opinion?

hr

Depends on the application

Copper tube boilers are great for snowmelt applications. Lots of power in a small package. They like long steady burn times under fairly constant loads.

Water quality is critical. Hard water can scale up the tube heat exchangers quickly, even the initial fill water. Check with manufactures for their water specs. Glycol percentages are another issue to check with the manufactures on. Pump size is critical also, the need lots of flow. HXs should be checked and cleaned ocassionally, and don't let them condense!

Hard to beat a cast iron for long life and trouble free service. Once again, watch return water temperatures to prevent condensing mode runs.

Stainless modulating condensing boilers are making great strides these days. Very well suited for low temperature radiant applications, with multi loads.

Lots of choices these days. Enough to make your head spin! Go with a brand that has good reps and support in your area.

Select the boiler based on the application.

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Duncan

Amen!

"Select the boiler based on the application."

What's your application, Alex?

Alex Ma

Space heating

My projects are mostly space heating with baseboard fin tubes.

hr

It's the multi zones

and micro loading that challanges low mass copper tube the most, I've found. For example if the total design load was 100,000, and this was broken into 5 zones.

It may be possible for only one or two zones to call. When this happen the low mass boilers tend to short cycle. Frequent, short "burner on" cycles may lead to flue gas condensation. It will depend, also, on the type of flue and length. Flues through unheated space (attics, outside flue chases, etc) will suffer from flue gas below the fuel dew poiunt causing corossion of the liner and eventually plugging the HXs, if the burner on time is insufficient to warm the entire flue run.

With low mass boilers two stage firing helps alot, modulating gas valves, and adding a buffer tank to lenghten the burn cycles.

I rarely see copper tube go much more than 15 years even under ideal conditions. You'll notice 30 year plus cast iron boilers pictured here on a regular basis Food for thought.

These issues tend to disapper with high mass, larger water content boilers. Still the application will best dictate the equipment choice. There is a time and place for both type.

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Steve Ebels

My humble opinion, bluntly speaking

There are only two materials suitable for heat exchangers in boilers. Iron and stainless steel. Properly installed, I think a cast iron boiler will outlast just about anything as far as heating equipment goes. Stainless is better when you get into condensing type applications for obvious reasons. Add a modulating burner to that and you have a near perfect heat source. I always wondered about the systems that I have seen with low mass boilers driving them and a big old buffer tank to keep the thing from short cycling itself to death. Where's the low mass in that? I don't think I have ever run across a copper "boiler" over 10-12 years old unless it has had truly exceptional care and maintanence.

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Boilerpro

How many copper tube boilers have you seen properly installed?

Around here most contractors install them like they were old high mass boilers from the 1940s, so its no wonder there are problems...similiar to the problems we are now seeing with new low mass cast iron boilers and condensing boilers. Single zone baseboard system with properly sized copper tube boiler and pump should give good life... maybe longer than new low mass cast iron due to the thermal shock that occurs whenever the pump first kicks on. Full flow cold water from the baseboard hits that low water content cast iron boiler pretty hard with full load delta tees of 60F or more. If you go cast iron, I would pump continuously to give you better boiler life.

Boilerpro

hr

A lot of the copper

boiler issues started with the manufactures and reps! They claimed 100- 110 return temperatures were not a problem. Raypak, for one tried to handle that with a little factory built bypass tube and valve. I don't agree copper tube can run continously below the dew point of the fuel without a problem, someday. It make take a few years, but you will see problems. from my experience.

As you know pool boilers have "built into the header" thermostatic bypass, to accomodate 80 degree or cool constant return temps.

The higher volumn, large water content cast have for years handled the cool returns without any problem. However the current cast are much less mass (weight) and water content. Not much more weight than copper tube these days! So return protection, even with low mass emmiters (baseboard) is becoming more of an issue, I feel. Thermostatic mix valves, electronic controls, etc should be standard equipment on installs these days to be sure the boiler is protect and lives a long, happy life

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