Really, really, really, big pipes in hot water heating system

I have hot water gas heat in a 1920's house. Most of the original cast iron pipes in the basement are exposed and some of them are absolutely huge (5" diameter). My understanding is that the original system used gravity rather than electric pumps to circulate water through the house so the extra volume was required.

As my heating bill continues to climb (it's getting cold in New England), I'm wondering if it is worth a long term investment to address what I expect is a real waste of energy. I figure I am paying a ton of cash to heat much more water than I need to since it just sits in the pipe. I also expect that motors in the system are working extra hard to move the high volume of water.

What I want to know is how to determine the best "ROI" for one of the following:

Option 1: Replace the large pipes where possible (do not rip open walls, etc.)

Option 2: Insulate the exposed pipes (none are insulated).

Option 3: A little of both?

Option 4: Do nothing. The extra energy required is nominal.

Anyone ever dealt with this situation and determined the best course of action? If I do anything, I do not really want to wait 20 years for the pay-back on my investment.

Thanks,

JT

heat

#1 and #2. The smaller volume of water will give you a higher circulation velocity, so the radiators will heat more efficiently.

HJ,

Any sense of how to get a rough calculation on the savings? I figure replacing these pipes is no small cost and if it just going to cut 10% off my bill, it will probably never pay for itself.

-JT

A friend of mine had a similar system (if I remember correctly), and when he had it analyzed (Canada is stricter on this sort of thing), his ancient system was actually quite efficient. He left it alone. Can't say for sure about yours.

Pumps?

Depending on the piping system, this large diameter thing you have going could be really efficient. One component to check out might be the pump(s). If this was an older conversion from a gravity system, the pump(s) might be a big power draw. I'd get a pump dude over to have a look. Make sure its the appropriate gpm, etc., Do the pump curve thang. Insulation's a good thing too.