Best Of
Re: new concrete slab with radiant heat that will be polished for finished flooring
we had a concrete expert at an RPA convention yeas ago talking specifically about radiant and slabs. His suggestions
When you pour a slab within 4 concrete walls you can get external restraint cracking. Always have a bit of an expansion strip around it. They have a dense rubber foam strip at the concrete suppliers for this1/2 wide 4” deep.
The larger the aggregate the stronger the concrete mix, go with 3/4 or larger.
The mix leaves the plant properly mixed. Every gallon of water added to a yard of concrete reduces the psi by about 100 lbs. use a plasticized if you need it to flow better. If they add5- 10 gallons when the truck arrives to make it easier to “pull” your odds of a crack increase.
Rebar, heavy remesh, nothing guarantees a slab will not crack. The steel keeps the slab from shifting where a crack goes through a slab. A crack is a free control joint :)
The subgrade below the slab has a lot to do with the integrity. On commercial work they do compaction tests. I have seen a few jobs fail that test and the subgrade had to be reworked,
I would use a base rock at least 4” and compact it.
I had a finished, colored slab in two of my office/ shops, color was mixed in the batch at the job, and no, they do not like doing that and may charge extra! Actually the color sort of wore through where we walked the time all you would start to see some aggregate.
How large is the slab? Control joints are on a 10x10’ grid. I have poured jobs without any control joints for custom basement colored slabs.
Know that when you saw cut a colored slab you will see white stripes as the aggregate is not colored! Usually you caulk those saw cuts with a colored silicone.
Ideally a control joint is 1/3 the slab thickness, which is not doable with tube. Best you could gamble would be a 1” deep cut if you have tube 2” below the top. But a crack will travel across a 1” cut. I’m not convinced any type of control joint is 100% able to prevent or stop a crack. It the tiny little cracks, called road mapping, that drive me crazy in finished slabs. Prepare your self for those.
A troweled in joint will not look good at all. It would be a wide joint to caulk nicely?
While the mesh is great for tying tube it does little to reinforce the slab, especially if it is not lifted.
Yes the fibers look like dog hair on the finished slab, but if they power trowel it melts them off and they are not noticeable.
The recommendations from the speaker were to increase the fibers to 3 lbs per yard, do not water the mix, add agents if it is extremely hot, as a fast dry day can be an issue. On hot summer pours they would spray a coating on them as soon as the finished troweling, supposed to slow the water from leaving the top.
The slabs that looked the best to me over the years were stamped or stenciled ones, they hide cracks well. I did one job where it was stamped to look like wood planks! It was a little rough on the feet however.
Hoping to get a perfect, long lasting crack free polished slab is risky business. I doubt any plant or concrete finisher would guarantee that. It is a hard unforgiving surface, in kitchens especially. But tile is also should you drop anything on it.
I would tube it 6” oc to operate at the lowest SWT, minimize expansion/ contraction. 3/8 is easiest to work, but 200- 225’ loops. You get a tad more concrete coverage.
Pros and cons to high mass vs low mass radiant. Slabs need to be set and left circulating imo. They do not ramp up or down quickly.
I will say in a shop in a cold climate, nothing beats a warm slab. Concrete is a tricky medium to work with, and it is pretty final. Concrete is the most consumed product in the world. Looking at some of the structures and roadways the build in China, they must be the largest consumer?
hot_rod
Re: Prevent mold in mini-split heads
Beside creating issues with humidity removal, oversizing will generally mean more crud on the coil. Crud builds up on the coil when the coil is allowed to dry out after running for a bit, this slowly bakes on the dirt which leads to blocked airflow and smelly coil.
I can directly see this with a couple of the mini splits I maintain. There is a set that are way oversized and the coil is always filthy. The right sized ones are pretty much spotless.
If you think about it this makes sense. If the coil is always running, there is generally condensate collecting and flowing down. This cleans the coil so dirt won't build up.
I have also noticed this effect on outdoor units. Because the heat pumps have a lot of condensation on the outdoor coil during the heating season, they stay pretty much clean.
So if you want a mold free unit, make sure to about right size. The typical rules of sqft/ton are always wrong.
Kaos
Re: Warm Start Boiler Summer Leak
I would guess not. Since this is a WTGO boiler it was equipped with a tankless coil, that would mean to offer DHW priority the circulator would stop pumping cold radiator water when the aquastat reached the low limit circulator cut out temperature. The boiler would always maintain 140° or more if the low limit was set at 160° with a 20° diff. No need for boiler protection in this case.
Now that the cold start boiler is an option, they may need to think about boiler protection with a bypass of some sort, or some reverse strap on aquastat that keeps the circulator from operating when the supply temperature is below say 150°. the circulator would cycle several times as a result, but it did that when it was operating for DHW anyway. So no big deal.
Re: ECM pumps interfering with each other
Each radiant pump is serving many loops. The fan coil pump is serving 3 fan coils. This is great information. Thank you.
Tomorrow is Install Day!
With the help of a few friends the SS liner will be installed tomorrow morning.
I shut down my coal stoker boiler as my coal supply was ended and removed the old flue pipe. Then vacuumed the remaining fly ash and cleaned the thimble.
Just for fun I stuck a mirror inside and got a view of a clear shot to the sky!
While we are up on the roof I will make a template up that will serve as a guide for a SS fluecap for all 3 flues. That will be a winter project !
Next will be to "unpipe" the old boiler and start the new install.
Re: 3 and 1 1/2 ton finally done
I can't wrap my head around the min height thing. We do it on gas furnaces just to follow the written word.
AC—-can't see how that can possibly matter
GW
Re: Summer shut down and 8 way treatment
yeah, we make our own demineralized water with a demineralizer unit that we hook up to city water. But the output of the demineralizer is like a ph of 5, so we use a chemical from Rhomar’s called ph boost to bring it back up.
