Basement floor seepage and my boiler

[Paul Puccio]

So this is strange but here it goes.

It appears that every time my boiler kicks on, water starts to seep up from the basement floor, about 4 ft away.

That's the short of it... my wife had this suspicion last year, but I couldn't/wouldn't believe. Then the summer came along, no seepage. Then the other day, she's in the basement exercising and sure enough, the boiler kicked in, water started coming up. I choose wisely and agreed with her that she must be on to something. Does it happen every time? Not sure, haven't done a true analysis of it yet, but there definitely seems to some correlation (but that doesn't mean causation).

The house was built in the late 50s and the boiler is probably almost as old. We've been lucky, but we know that might have run out... we've been preparing for the replacement boiler.

So, has anyone heard of such a thing before?

Thanks

 

[Dana]

Is there slab radiant heating in the basement?

 

[Sponsor]

 

[djdavenport]

Post hoc ergo prompter hoc. It's a classic. But by sleuthing around a little, you can probably figure it out. Is the water coming from the boiler? Well, is the boiler losing pressure? Do you have an auto-feed system that might be disguising the fact that you're losing water? If so, shut it off and monitor the pressure. If it remains steady, the seeping is not coming from the boiler. But maybe still boiler related. If you've got hot water going through the slab and there is rogue water trapped underneath, could the slight expansion in the slab be squeezing that water up through the floor? Possible. Or maybe your house is simply built on the seasonal-related artesian well. But I kinda doubt it.

 

[Dana]

The house was built in the late 50s and the boiler is probably almost as old. We've been lucky, but we know that might have run out... we've been preparing for the replacement boiler

An Eisenhower era boiler is at least 2x past a normal lifecycle, so sure, it's (past) time to think about replacement, even if it's not the cause of the slab moisture issue.

Homes of that era have usually be significantly upgraded for efficiency over the past 60 years with better insulation, windows, more air- tightess, etc, and it was common for boilers to be 2-3x oversized even for the heat load of the house in it's original condition. Replacing like-for-like is almost always a mistake, for both boiler efficiency and comfort. (ASHRAE recommends 1.4x oversizing for non-modulating heating equipment as the best compromise on comfort & efficiency, but you can go lower with modulating equipment.)

To get a handle on the heat load, comparing last winter's fuel-bills with exact dates & amounts against heating degree-day data makes it possible to use the existing boiler as a measuring instrument to determine the heat load. The methodolgy for doing that lives here.

If considering a modulating condensing boiler the minimum fire output is more important than the maximum fire output. This is because at water temperatures necessary for getting condensing efficiency the radiation puts out less heat. The temperature of the boiler is normally set up to vary with outdoor temperature to always cover the heat load of the hour, but the radiation and min-fire output determines the minimum water temperature at which the system can operate without short-cycling. It's not hard math to get it at least in the ballpark, but surprisingly few installers run those numbers. The napkin-math version of that analysis is outlined here.

When running a fuel-use heat load number using the boiler as the measuring instrument there is no need to derate the replacement boiler for altitude from the derived number, nor it it necessary to use IBR net water derating, since all of the distribution losses and altitude derating is built into the fuel use load number (indeed, it's not possible to separated it out.)