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how much efficiency loss from a leak in the loop?

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Posted by Scott on August 01, 2011 at 14:49:33:

I've got a hydronic system in a 1942 house. I posted on here a while back about my old National Boiler and got some great suggestions.

Two summers ago, when NatGas was spiking, and there were discounts, I went to a super-condensing boiler (Buderus) and replaced the old cast iron lump. The new boiler should have been a nearly 50% jump in efficiency. I got almost no change. It is maddening.

I found, while working on some bathroom plumbing, a leak in the hot water loop under the house. A decade ago I had central AC installed and the installers said "we need to move the pipe for the loop to clear the path for the duct work". I said, um, OK.

They took out part of the old black iron pipe and replaced it with copper - just a slight dog-leg. 1.5" K-copper. However, they did a lousy job sweating one of the joints. It has been seeping for ten years!

The first winter after the AC was installed, my tennants (this is a rental) complained about lousy heat and insane heating bills. I came over and bled the system...several times...I gave up and put automatic vents on most of the convectors.

That solved the need to bleed by masking the problem! There was always a huge tendency for the system, when closed, to lose pressure. I tried draining the pressure tank (in case it was water logged), etc. Always: this problem. Finally, I gave up and just said, gimme a new boiler. And the boiler makes DHW too. No change in the heating bill. The feed was left on, so I never really noticed the leak.

Well, clearly this leak results in a constant bleed in of cold water into the system. Probably lots of oxygen too (no good). So, while it's summer and I'd prefer to be under the cool crawlspace, I'm going to fix this.

My question: how much of a difference in efficiency can something like this make?

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