Running radiant off steam boiler?

Steve Garson_2

I have a new SGO-4 boiler for my steam heat, with Vaporstat, and an Everhot heat exchanger for a small baseboard loop. On the coldest days, ie 0*, the boiler runs less than 25% of the time, once the house warms up after a night set-back. Heat loss for the house is:
1. Room with baseboard: 13,000
2. Two rooms with radiant: 15,000 BTU
3. Portion heated with steam radiators: 47,000 BTU
Total: 75,048 BTU

The SGO-4 has been down-fired to 1GPH because all the air vents whistled at the standard nozzle. With 84% AFUE, that would mean I have 117,600 Net BTU available...I think.

My radiant system is heated by a 6-year old CombiCore water heater. Since my boiler does NOT run that hard, I was thinking that it might be cost effective to either add another Everhot or replace the one I have with a larger one to support the radiant and the baseboard. The gas bill for the radiant is only around 420 therms for the heating season. While a Munchkin with indirect would be a good long term investment, I can't cost justify it right now with my finances.

The heat loss for the radiant zone is 15,000 BTU. While the house has 435 EDR of steam radiators, with excellent insulation and windows, the boiler doesn't take a lot of effort to heat.

Does my approach make sense? What would you do if it were your home?

Brad White_9

I would add the load to the boiler

You have so much extra capacity you could export it. Just so long as the setup is sub-steam and below the waterline (in other words not a steam-driven Everhot), I see no reason that a properly controlled load like that cannot be added. Do you need a separate Everhot or can you piggyback onto what you have now? A mixing valve and not much flow, you may be able to fit that in. Just a thought.

EDIT: To be clear on my intent, a heat exchanger is essential as Paul Pollets said below. I would never suggest otherwise. Seal the system, keep them separate and the radiant clean.

Paul Pollets

Purging issues, et al

The issue with running radiant loops off a steam boiler would be filling/purging the loops, and mixing controls to allow low temperature setpoints. I've installed several "below the waterline" applications, including Indirect tanks and wall panel rads, but never a radiant zone without a heat exchanger

Adding a heat exchanger allows all the above.

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Norm Harvey

I agree with using a heat exchanger to run the radiant off steam.

The coice of exchanger is importaint. I would want a device that wouldn't be prone to mud clogging like a flat plate exchanger. A stainless indirect tank would be my preferance.

Heres some great diagrams: http://www.heatinghelp.com/heating_howcome6.cfm



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Steve Garson_2

Norm:

Why not the Everhot? I though that was what they are all about? What would you suggest?

The Everhot no installed is the RH6, rated at 6GPM, which is all copper with 2-inch boiler water supply and return and 17.43 sq ft of heating surface/200 sq feet radiation capacity. The GPM is based on 100* rise at 200* boiler temp.

Norm Harvey

Yeah the everhot is an option, certainly. I didn't think of that.

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Steve Garson_2

How do I determine what size Everhot I need? Or whether the one I have is fine? I would like to be able to get the hot water without the boiler needing to be at 212*.