convert Timkin Silent to new style water boiler

SethYank

My customer has an old Timkin gravity boiler with two loops. The boiler has two 2" connections on top of the boiler, one going to the front of the house and the other going to the back of the house. Is a three story house with radiators. The first floor is a separate apartment, they removed the radiators Years ago. the 2nd and 3rd floor has 6 radiators total, approximately 400 square feet of radiation. I am not sure how the radiators are split on the two loops. The old burner had a 1.5 gph nozzle, I am thinking way over sized. They want a quote to replace with natural gas fired water boiler, probably cast iron to reduce maintenance costs, rental property in city. My question is can I tie the two loops together and pump away from the boiler into them, will the majority of the flow take the easier path and leave the other cold? If I split and put two circulators one on each loop the piping probably runs vertical through the 2nd and 3rd floor so how do I place thermostats to control it?

Jamie Hall

Gravity hot water conversions are quite feasible, but... you HAVE to install balancing valves on any risers or anywhere the mains split, and it can be a bit tricky to get the water to flow where it is needed. Where you have risers serving two floors, you will probably also have to adjust the radiator inlet valves themselves to persuade the water to go where it's needed.

As you note, water is lazy,. and unless you use balancing valves it will take the easiest path -- and in old gravity conversions that usually means the lower floor or floors will be warm and toasty and the upper will be cold.

Whether you want two thermostats or one depends on how the floors are split. If they were split so that each floor was a separate zone, then you could have one on each floor controlling its own pump or zone valve. If they are split vertically, you could have one if you liked for each side -- again, each controlling its own pump or zone valve.

SethYank

So putting balancing valve on the return lines from the two zones, how do I balance them. Take supply and return temperatures and try to equalize them?

Steamhead

Also, they need to do a heat-loss calculation on the house to properly size the new boiler. if they do not, they're likely selling you a boiler that's way larger than you need.

SethYank

I already figured the load is about 50kbtu, so the 1.5 gph is way oversize

Jamie Hall

Balancing is best done by assessing the comfort -- or temperature or both -- of the spaces involved. Seems a little tedious and experimental, but it works.

mattmia2

There also may be orifice plates in the unions of the valves of the upper radiators that help encourage the water that is flowing by gravity to flow to the lower floors, you may need to move those to the lower floor or remove them because once it is pumped the water will prefer the closer emitters rather than the higher emitters. Keep in mind you don't need crazy flow through this too, the circulator should be sized more on the size of the boiler and how much water needs to move to move that amount of energy than on the size of the gravity piping.