Cast iron boiler design exercise

MIke_Jonas

Neighbors' house. Converted gravity system. Boiler oversized. Cast iron radiators. Pump runs 24/7. This summer I'm going to install a properly sized Knight, put trvs' on the rads, generally clean it up and make it presentable.

In the mean time, 15 year old B & G 100 went kaboom Friday, coupling pieces found on the floor. I installed a 3 speed pump, Grundfos 15-58.

Since they were gone Sat & Sun, and I have a key to check on things, I hooked up my handy dandy Fluke 54 and recorded temps on the different speeds. House stat set to 70. Data logging every 30 seconds.

Low speed...delta T 21-23d. Absolutely quiet throughout the house.

Medium speed..delta T 18-20d. Some (faint) noise in one upstairs radiator, the tallest one in bathroom.

High speed..delta T 12-14d. Noticeable noise from upstairs rad. (to me, anyway, my wfe couldn't hear any of it)

I have, but am not listing, max supply temps. I started this last night, when it was about 0d out. I finished this afternoon, and it's about 20d out, so the run times and max supply temps were higher last night than today.

I'm content to leave it on medium. What else would you look at and why?

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Steamhead (in transit)

Medium

sounds good to me. The ΔT is about what you're looking for. If all the radiators are getting good circulation, there's no reason to run it faster.

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