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Insulate pipes on converted gravity system for quicker warmup?

JeremyG Member Posts: 16

My 2-story, 1600 sq.ft. house was built in 1935 and appears to have originally been a gravity system with 2" iron pipes closest to the boiler. The 1983 cast iron boiler is 167 MBTU/H using natural gas (Weil-McLain HE; fan-assisted), which is about double the heat loss according to a Manual J from earlier this year.

I've been in the house a little over a year and recently learned about the risk of not letting the boiler get hot enough (140º F) to remove condensation from gas combustion. My Ecobee thermostat does a great job of keeping the temperature within 0.5º, but that meant runtimes of less than 10 min in the shoulder seasons. Yikes. After a little trial and error, it seems like the boiler will hit 140º in 15 min, so I've set that as the minimum runtime on the thermostat. I also looked at the heat exchanger with a mirror and it looks somewhat rusty. I have no expertise to evaluate how bad it is, and I guess at 35 years old it could leak at any time.

So, I want to do what I reasonably can to keep this boiler HX from failing while I'm planning how to finish the basement (incl. relocating the boiler) and boiler upgrade path. I've gleaned from this site and the W-M manual that there should be a bypass loop. That makes sense.

None of the pipes in the unfinished basement are insulated. I'm wondering if that might help get the boiler up to temp quicker? It looks like 1" fiberglass insulation would be about R-6 for a 2" pipe. Access is good for the pipes > 1" (~75' total) and is something I could do relatively easily. Seem like a good approach? Any others to consider?



  • JeremyG
    JeremyG Member Posts: 16
    I came across the Taco Viridian Delta-T circulator after doing more looking around. It has a "boiler protection" feature that keeps the pump at the slowest speed until you hit a configurable minimum return temp. That might be a good solution, and is about the same cost as fiberglass pipe insulation (and much less labor). It also would avoid plumbing work, which I'd like to avoid until it's time to replace this beast. My initial head loss calculation was rough, so I need to improve that before deciding to buy anything.

    I also tallied up the EDRs of my CI radiators and found that I have about 120 MBTU/H at 180º. And now the sizing of the boiler makes more sense... the installer probably matched it to the emitters and rounded up to the next size unit (137 MBTU/H net).
  • sputnik99
    sputnik99 Member Posts: 7
    Your setup is very similar to mine, CI radiators, gravity system pipes with circulator, etc.

    I also have an Ecobee thermostat and set the heat differential to 2.5 F (1.4 C). I put on a sweater and keep the house a bit cooler at 70 F (21C) and it drops to 67.5 F before the thermostat calls for heat. This increases the run time and I suspect is more efficient vs having multiple shorter runs since it takes a bit of time for the water to heat up coming from a cold start.