Boiler Poured Concrete Slab Base vs. 5 Cinder Blocks?

cubicacres

We had our EG-75 steam boiler installed on 5 cinder blocks on the rim of the boiler footprint in our boiler room & it looks like one or two of the blocks may be supporting the iron boiler block itself one end. This might let us notice some water leaking from the boiler if it has any future leaks, compared to a poured base that might hide some water (or so we hope). The 3 inches or so of extra height doesn't interfere with our dimension A. Our old boiler was directly on the floor with no slab or cinder blocks, and was very corroded.

Does anyone have any thoughts/experience about using cinder blocks with some of the tapping cut-outs as pads/shims to level it? The install manual recommends a larger full-size slab, but I noticed no lower part of the boiler was touching the center space underneath the boiler, so I'm wondering if the blocks are just as good? In the back of my mind, I'm wondering if future movement might cause a cinder block to shift or break, tilting the boiler and prying a seal off?

Jamie Hall

If the cinder blocks are mortared in place, then I'd have no real problem with it. if they are just sort of slung under there... sloppy workmanship, and I'd sort of be wondering what other corners were cut.

Be happy, though. It is much much better that they raised the boiler up on something. They may not have been thinking about wet returns, but it's amazing how often wet returns are converted to dry returns because someone didn't set the boiler at the right elevation. With catastrophic results.

ChrisJ

Jamie Hall said:

If the cinder blocks are mortared in place, then I'd have no real problem with it. if they are just sort of slung under there... sloppy workmanship, and I'd sort of be wondering what other corners were cut.

Be happy, though. It is much much better that they raised the boiler up on something. They may not have been thinking about wet returns, but it's amazing how often wet returns are converted to dry returns because someone didn't set the boiler at the right elevation. With catastrophic results.

I don't think I've ever seen a boiler up on blocks that were mortared? Maybe I keep missing something when others post pictures.

Dave0176

Poured concrete slabs are the best and the nicest looking, however we may not always have the time needed to set up and let the concrete cure, as a lot of boiler replacements are emergencies and need to be done ASAP.

I usually use the regular 4" high concrete blocks.

Jamie Hall

The only reason I'd like to see a thin bed of mortar under the blocks is the it reduces the chance that vibration will shift them. Just fussy, I suppose...

Mark Eatherton

Most conventional gas fired boiler manufacturers whose boilers are not rated for application on a combustible floor show a detailed plan for the use of cinder blocks, with hollow cores for the boiler base, to allow the downward radiant energy to be dissipated and avoid carryover and flashing for wood floors.

The amount of downward radiant energy from an open atmospheric burner is fairly significant in some cases. I once saw a job where 1-1/2" of gypcrete was poured on the second floor of an apartment complex. The framing beneath the gypcrete flashed over, caught on fire and the boiler fell through the floor.

I saw another job where the contractor used a catch pan as the fire resistant shield beneath a CFT boiler that also wan't rated for use on a combustible floor, and it too caught the joist on fire, but that was because the homeowner decided to "test" a new indirect DHW heater we'd installed, and left the shower running for 3 hours to see if it would keep up... It did, but it caused him mechanical rom floor to catch on fire. Fortunately for him, the fiber glass insulation in the joist bay cavity didn't allow enough oxygen to let the fire really catch hold...

Charlie from wmass

I use solid blocks for my boilers when there is no time to wait for the concrete to cure. I had a job where I rushed putting the boiler on the poured pad and I chipped the corner, the customer insisted on a new poured pad. This meant removing the new boiler and resetting it after the new pad was cured for 24 hours. I was glad I used unions and it was only a 4 section Independence boiler. Lesson learned. I will keep in mind the hollow block ( Thanks Mark) for boilers on wood flooring. I seldom see that anymore as my boilers are either steam or wall hung for the majority of the time.

JUGHNE

When possible, I have put at least 4" (actually 3 5/8") solid blocks under anything I install on a concrete floor, even slab on grade.

Some mechanical prints refer to a concrete pad as a "housekeeping pad"... this keeps things up and helps avoid the dust "bunnies" that could accumulate under every thing. Also IMO it protects the bottom of anything not only from basement floor condensate, sewer back-up to a point and attacks by vacuum cleaners, bowling balls, skateboards etc. Also raises equipment up that 4" which seem to really help out your back and knees for servicing, (in the event you get older).

I even put my water softener up on 4" blocks just to define it's space.
Our first boiler (100,000) was on 4" blocks to help convince my wife that that little box would heat our new house. The new 80,000 Mod Con is up on 8" blocks for the same reason.

There was one CI HW boiler that I replaced that had bad support for the base which contributed to it's failure. It was on an uneven floor and was sorta shimmed on the corners. The lack of support caused the rails/burner box which supported the CI sections to distort the entire boiler. This warped the burner supports and caused the flame to burn thru the cabinet with the escape of fumes from the side. After patching the burner box a couple times it was time for change out.

However hollow blocks on their side are fairly weak if a heavy load has only 4 legs and the 1/4 of the weight is applied to the side of the hollow. I would use 8X8X8 solids for the 4 corners and fill in the remainder with standard hollow core to get the air cooling for the radiant heat attaching the floor below.

bob_46

combustion efficiency ? if the boiler doesn't have a metal bottom under the burners you shouldn't put it up on blocks unless they go all around the perimeter . You will significantly increase the secondary air. I always wonder how many techs put the door on the boiler before they check CO2 . Back in the 60's I went to school at Weil McLain, shake bottle days, and they had us measure CO2 with the door on and off. It makes a difference.