Steam, Hot water baseboard and Radiant

Steamhead

can't be very efficient for heating, and you have to adjust it manually when it gets cold. So here's what I would suggest:

Install a new steam boiler to operate the steam system, and a hot-water boiler to run the baseboard and radiant. You could continue to use your existing water heater as a domestic-water-only unit, or replace it with an indirect heater which would run off the hot-water boiler.

This way each boiler would be sized to the load it would carry, and the whole house wouldn't go cold if one boiler broke down.

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Steve Garson

Steam, Hot water baseboard and Radiant

I have had a couple of heating people I found on this site come in to quote on replacing my boiler. I haven't heard back yet (gentle nudge:), but the two suggested different approaches, so I would love to get some feedback from The Wall.

Present system: 70 year old steam boiler heating 461 EDR before counting the pick-up factor. Boiler also feeds a 33-foot baseboard hot water loop for a room with 13,000 heat loss.

There is also a radiant loop heating a heat loss of 15,000 BTU with Onix staple-up. This is heated with a Bradford White two-loop gas water heater, along with the household hot water.

Contractor A: Suggests replacing the boiler and keeping the baseboard zone running off the boiler water. He also suggests keeping the radiant heating the way it is. The water heater (Bradford White Hydrojet 46 gallon 65,000 BTU) is only 4 years old.

Contractor B: Suggests running the baseboard off a tankless coil, which would also be used to heat the radiant heat, with outdoor reset and a mixing valve for the radiant. My radiant needs a water temp of 150* on design days, 140* when it is 15* to 30* and so-on. Today I adjust the water temp manually on the real cold days.

Building heat loss for the steam heated portion of the house is 50,000 BTU. Building is as insulated and sealed as is possible, so improving that is not an option.

Oil usage (steam and baseboard): 780 gallons for this
heating season

Gas Usage: 350 Therms for this heating season.

What are your opinions on one approach versus the other?

Steve

Steve Garson

Are there boilers small enough for the mere 25,000 BTU heat loss. An 85% boiler would be around 30,000 BTU input. Can they vent into the same flue?

John Shea

Not totally sure it's possible, but...

it would be worth checking into a steam boiler using the condensate for hot water baseboard and the radiant.

My thoughts are based on Dan's book, "How Come?"

One boiler for all the heating would be nice. It may require more controls than usual, but cheaper install/maintenance than two boilers.

Steamhead

Sure there are

I think Burnham makes some very small ones. I seem to remember they had a steamer rated 160 square feet or something like that.....

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Steve Garson

Can I vent two boilers in the same flue?

If I go with two boilers, can I vent them in the same flue as long as the flue size is large enough? Right now an oil boiler and gas HW Heater vent in that flue. I would be adding a gas boiler to the flue.

Steamhead

As long as it's big enough

I don't see a problem. But it would be well to check with Code authorities in your area, as regulations vary.

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Steve Garson

I was just checking the numbers. My radiant system used 340 therms for the heating system. If a separate boiler were 20% more efficient that the four year old Bradford-White water heater, I would save around 68 therms, or around $90/year at today's prices.

The baseboard loop is 20% of my present boiler's heat load. With 750 gallons of oil used, 20% means that 150 gallons were allocated to the baseboard loop. If this ran on a separate hydronic boiler, versus as a loop off the new steam boiler, it would save 30 gallons a year, or around $60.

Combined savings might be $150/year, for a 10 year+ ROI, assuming that these savings numbers are valid. Seems like an iffy decision to install two new boilers, doesn't. The combined heat load is 27,000 BTU.

Steamhead

You'll save more

as fuel prices go up. So your ROI will probably occur sooner. How much sooner depends on how far prices go up- but we know they will go up!

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