bypass loop for replacement boiler with radiators

Mark J Strawcutter

a Danfoss/ESBE thermic valve on a system (vs boiler) bybass setup. Works with or without P/S

Mark

[Deleted User]

bypass loop

Replacing old oil fired boiler with new gas fired boiler with old radiators. Should I install a bypass loop to protect the boiler from cold return water from radiators. Is this a big concern?

Unknown

yes, and yes

Noel

Ben_3

Primary/ Secondary

I like to Primary/Secondary all my boiler installations. There are way to many advantages to list, cold returns and boiler protection just being one of them

Boilerpro_3

How does P/S piping by itself protect the boiler?

Richard D._2

By-Pass

is a MUST HAVE,reduces thermal shock and keeps the boiler hotter longer helping to prevent condesation in lo stack temp. boilers...Interested in the Primary/ Secondary reasons!!!With raditors in a average res. home..Richard

hot_rod

A bypass without

a temperature activated control is a guess, at best! A three way thermostatic mix valve would be one simple way.

Primary secondary will work IF you have a sensor at the boiler return to shut down the load circulator when or if the boiler return drops.

Viessmann uses a simple, but effective, non adjustable 140F aquastat in the boiler return that shuts off the boiler circulator when the return falls below 140F, on some models. It works well. Don't try this on a copper tube boiler, however

You really should take the steps needed to offer your new boiler investment return protection. Modern day cast iron boilers cannot handle the slugs of cold return water like the behemoths of days gone by, and they may reward you in expensive ways.

hot rod

Boilerpro_3

I'm with you, HR

A bypass is below minimum in my book, even if it is what most boiler manufacturers have in thier instructions. Around here, it's hard to get installers to even put in a bypass!

Boilerpro

Ben_3

P/S

I prefer this over a simple bypass, I agree a bypass is the bare min., In these applications I install a bypass as well but found after fine tuning the system this valve was almost always completly closed if not totally closed. In a single zone application I make the system the primary loop and select a pump to move the gpm @ low head at a 20 deg. delta T. Then I pipe the boiler as the secondary loop. I can select a pump to handle the load and run at whatever delta I choose, mant times between 20 and 30 degrees. Half of my installs go in with a copper boiler where this is a must. BY selecting a larger delta across the boiler I don't need to move as much gpm and the ABC's of return temp will apply to the returning water to the boiler. Also alot of my installs are multi-temp-multi-zone applications combining many different types of radiation. P/S gives me the ability to control these temps perfectly. In these cases I use the boiler as the Primary loop and the zones as secondarys, unless of course, this a multi boiler setup then I have one main primary loop and the boilers are secondary as well as the zones. Its all in the delta you want to run for the required load and gpm for that delta. This also works extremely well with condensing boilers to ensure a cool enough return temp for efficiency. A simple bypass will never give you this kind of control. However I still put a bypass in but like I said they usually end up closed and not needed since I'm keeping all that cold water from the old gravity system isolated in it's own loop and mixing it with my boiler water. You can even leave the old system gravity and use your pump for the secondary boiler side just to supply the heat to the gravity primary loop. The options are endless and it works great for reset options as well.

nick z.

By pass

Many of the dead men in our area would cover every outside wall with cast iron B.B.talk about thermal shock when that cold water hits the boiler.I find it hard to sell the P/S. So I use a Venturi T in my by pass. Afert ajustment I remove the hanlde to the valve a ty- wrap to the pipe.