Boiler sizing and piping for condensation

dineshj

Hi,
I had a Laars JVS boiler installed a few years ago. Below is an image of the piping.
There are two by passes. The half size was installed initially and then the contractor came back and installed the full size bypass.
The pipe in the front is the supply and the back is the return side.
In the last two years, I have noticed condensation corrosion in the vent pipes. Now, I have closed off about 80% of the ball valve that supplies hot water to the system (the bypass ball valve is fully open). So only 20% of the water goes into the system and 80% goes back to the boiler. I have noticed that even this is not enough as it takes about 1 hour for the boiler to reach 130 degrees. Even when it's not on a cold start, the temp gauge is always around 120 degrees.
There is a lot of water in system. About 45 gallons! The circulator is Taco 007. 1/25 HP.
The sq footage area of the home is about 1300. The output of the boiler is 64K BTUs. I have cast iron radiators.



Thank you.

hot_rod

Cast iron radiators? If so you have a lot of mass to warm up, the water, steel pipe and radiators.
It would be better to have a thermostatic valve in there. It would automatically adjust the bypass flow to whet the boiler needs.

There are a few threads going on here about boiler protection valves.

Another issue you will have is never getting 100% of the boiler output to the radiators. When it does start to catch up with the load, you may get short cycling of the boiler. Too much returning thru the bypass.

Was a heat load performed when the boiler was installed?

dineshj

@hot_rod yes, the contractor did a heat loss calculation based on insulation and windows of the house. But he didn’t size the radiators. 

Teemok

They make a 140F version. hot_rod likely has advice on on the correct one for you. https://www.supplyhouse.com/Caleffi-280175A-1-1-4-Female-NPT-ThermoProtec-Thermostatic-Mixing-Valve-130-Degrees-F-Tset

hot_rod

As you have discovered it’s the radiators that drive the operating condition of the boiler, not vice versa,

It sounds like you have more radiation than the boiler output can keep up with.

If energy upgrades have been made, that is a common condition.

A mod con would be a great fit for a system like yours, possibly running at maximum 140F!

In the mean time, you need to protect that boiler. Copper tube boilers can plug up and corrode the fins inside when they run in condensing mode.

Hang a CO detector in that room😳

dineshj

Hi @hot_rod. What if the boiler is cleaned and the thermostatic mixing valve is installed?

Are saying the vent gases would stop flowing through the boiler and the vent?

EBEBRATT-Ed

@dineshj

The concern is that your boiler has a fin tube heat exchanger. Think of it as a car radiator. The gas flame is under the "radiator" and above the radiator is your chimney connection. So the gas flame burn the flue gas rises goes through the radiator where they give up their heat to the water and go up the chimney.

If your water stays below 130ish the heat exchanger can sweat and some combustion products can stick to the fins blocking them. This takes some time to happen but yes I would have the heat exchanger cleaned and the boiler serviced and a proper bypass valve installed so you can run it this heating season.

Then you can have some time to see what changes need to be taken with your system

I would recommend a valve with a temp sensor installed on the return