Best Of
Re: Installing wifi-smart thermostat with 2-3 wires hydronic heat-only
TR100VA004 is a multi-tap (480/277/240/120 volt) primary 24 volt secondary, TR100VA002 is a single-tap 120 volt primary, Other than that, they're identical. You should be able to use either one, be sure to cap off the unused primary taps individually if you use the 004.

Re: Why would my pressure relief drip leg leak a little?
Why do you think they call it a "drip" leg? 😂
But, seriously, you're supposed to replace those things every now and then, leaks or no, and it's supposed to be mounted upright. (I always save the most recent ones if they're not leaking, just in case the new one fails.) You're also supposed to test them now and then. If they don't close completely, they need to be changed.
Re: Why would my pressure relief drip leg leak a little?
The boiler being oversized is no excuse for operating a boiler at excess pressure. All that does is make the added fuel use and expense worse — as well as damaging all the vents and traps.
Crank it down where it belongs.
Re: Seeking your thoughts regarding a boiler/system upgrade for a small 1980s ranch.
If it ain't broke, don't fix it.
Does the present system work? Will your building inspector for the sale test it? He or she should…
If it does need a new boiler, get it sized correctly to the load. I wouldn't spend the extra to save the 5 percent or so on what a mod/con might give you.
Re: ? actual difference between hot water heaters from supplyhouses and big box stores
I can tell you for a fact that the Lowe's version of the Honeywell TH8110 thermostat has (or at least had, I haven't checked since I originally noticed) a different casting of the case, made with different plastic, than the supply house version. Who knows what other changes have been made.

Re: ? actual difference between hot water heaters from supplyhouses and big box stores
A co worker told me years ago he was talking to a DeWalt rep who told him the HD stuff had plastic gears and was not the same as you could by elsewhere.
Don't know it it is true.
I suspect some MFG dial it down cheaper to sell to HD
and I think others sell there standard products to HD if the price is right.
Re: Flow direction - baseboard heating
Hiring a $50/hr plumber will get you exactly what you pay for (an unlicensed handyman) good luck!
Re: Cast iron radiator output tables are wrong?
Does the burner ever reach the limit and shut off while the thermostat is calling for heat. The Ecobee run time is for the circulator pump run time, it may not be for the burner run time if the burner cycles at 160° off of the high limit.
Re: Battle of the thermostat: The science behind your central heating arguments
I strongly recommend taking the numbers off thermostats and then telling people to set them to where they are comfortable…
Re: Cast iron radiator output tables are wrong?
@DCContrarian and I had the same idea. I wonder if he is as smart as me?🤪