Combi boiler vs cast iron boiler with indirect HW tank

Steve Garson_2

I have a 30-year old WM GV4 boiler with an Amtrol 40 gallon indirect HW heater. I want to update these in the spring.

I realize that I will rarely be in condensing mode with a combi boiler, but being able to avoid the cost and space requirements of an indirect water heater makes me wonder if I would be better off with the combi boiler. Do they actually produce adequate hot water? I recognize that the cast iron boiler will last longer than the combi.

What would you install in your home if you were in my position and why?

Thanks for your feedback.

Steve

Hot_water_fan

I realize that I will rarely be in condensing mode with a combi boiler,

Are you sure? Even with baseboard, a condensing boiler can easily condense most of the year. The highest water temps are rarely needed.

GGross

I would install a mod/con with an indirect water heater. I would do this because I prefer to have a storage of hot water for various reasons. not least of which is that it is less at the mercy of your water quality, and good indirect heaters have a lifetime warranty for defects, often the wait for hot water is much quicker with a tank.

While I am not afraid of a tankless by any means, it is the kind of thing I don't push on someone, because they are really at the mercy of your water quality, and require regular maintenance. If you are used to having an indirect you will truly be happier with a tank than you will with a tankless.

Steve Garson_2

Yeah, my past experience with a tankless was with a cast iron boiler and it was not a good experience.

SuperTech

I'd go with cast iron with an indirect.  Keep it simple, reliable and durable. 

hot_rod

I’ve owned and lived with a number of different combis, got 16 years out of a Laars Mascot/ Baxi!

Yes you need to be patient, and some additional maintenance. Install them with tankless service ball valves, so deliming is a simple task. I never delimed any of the ones I owned. Ideally plate HX are somewhat self scouring if the velocity is high. That might be the reason they have such small plate heat exchangers in them, keep the channel velocity up?

You know the same minerals are lurking inside your Indirects, and coating out the coil surfaces.
I doubt many, if any check performance over the years. I’ve had the finned copper coil Indirects turn to a block of stone after a few years on hard water.

Steve Garson_2

If using a condensing boiler with an indirect HW heater, is the water heater heated from the combi hot water heat exchanger? Or heated from the same hot water loop as the baseboard, like it is with my large mass boiler?

hot_rod

The indirect is just another zone off the boiler
No need for a combi if you go with an indirect