Old steam system upgrade options

jimb245 · April 2019

After years living with nice simple gas-fired forced air furnaces, I now have this crazy old oil-fired steam boiler with two coils, one for domestic hot water and one for baseboard radiators installed in a newer addition to the house. The old part of the house has steam radiators. Besides the fact that the boiler will die at some point there are two short term issues: not enough hot water for a bath, and in one contractor's opinion the baseboard system wont be adequate to heat the addition during the cold part of a New Hampshire winter because the coil is not completely submerged in the boiler. Rules of thumb suggest the addition needs roughly 45000 Btu. (boiler rating is 180000 Btu, 530 sq ft steam). I've gotten two proposals from contractors and a third one from myself.
1) Add electric water heater with input from the tankless coil. Turn off boiler when not in heating season. This is relatively inexpensive. It would not help baseboard system, and maybe would not fit into eventual new boiler system very well.
2) Add a second small oil burner to take over domestic hot water and baseboard heating. Optionally replace the steam boiler at the same time. Each system would be in the $10,000-12,000 range. The idea of having to run two separate burners seems a little strange to me.
3) Add indirect hot water heater to the old boiler, and use one of the coils for the baseboard system. Eventually replace the steam boiler and use it the same way. Optionally add a second indirect tank for the baseboard system.

Sorry if this is vague and open ended but any opinions about what makes sense to do would be welcome.

Jamie Hall · April 2019

First question I'd ask is why is the baseboard system not submerged in the boiler? It should be...

However. That said. The simplest thing to do is to add an indirect -- using boiler water, not a coil -- to power the baseboard radiation. That is, the boiler water is circulated, controlled by an aquastat, to heat the indirect tank, which, in turn, is circulated through your baseboard system.

If all of the baseboard is below the water level in the boiler, you wouldn't even need the indirect -- just circulate the boiler water through the baseboards.

Then a second indirect -- bigger -- also heated with boiler water, not the coil, to handle your domestic hot water requirements.

Or... for the domestic hot water, install an oil fired hot water heater. They aren't all that big, and use some oil but not that much (they are a lot cheaper than electric!) and they have excellent recovery characteristics. Then you could turn off the boiler in the summertime. (bias disclaimer: all the places I care for use that scheme).

Steamhead · April 2019

Building on @Jamie Hall 's post, when are you going to replace this boiler?

You might want to consider putting the addition on its own hot-water boiler. If you do this, have a heat-loss calculation done to determine the boiler size. This same boiler might also be able to run an indirect for your domestic hot water, and if it's smaller than the steam boiler would use less oil to do so.

We have a customer with this setup and it works well for them.

mikeg2015 · May 2019

Probably need ot switch from the internal tankless coil to a regular indirect tank. Depending on age of boiler, more cost effective to just replace the boiler and add indirect tank and hot water loop at the same time.

Quick and dirty solution... install a 60 gallon electric tank as a buffer tank and backup capacity. Do you have a tank at all now?

jimb245 · May 2019

Thanks very much for the replies! They do help to make the options clearer.

I'm not sure why the baseboard coil is installed higher up on the boiler than the other one. It was added later so maybe there just wasn't room to put it lower. Eye-balling the coil position versus the boiler water level it does look like it's probably not completely covered.

No, there isn't any tank now, just the two coils.

EBEBRATT-Ed · May 2019

I am guessing your boiler has 2 locations for a tankless coil. 1 location (the lower one) is used on a steam boiler. The second higher location is used when the boiler is used on a hot water system. This used to be very common and many boiler were designed this way, they could be used on water or steam

Old steam system upgrade options

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