tie into existing boiler or get new tankless

ryanjj2

We have hydronic heating system with cast iron radiators on main and second floor. We have exposed floor joists in the basement . I would like to do staple up radiant floor heating for the main floor and leave radiators for second floor. Is it better to tie into existing boiler even though it will still be supplying second floor? Or is it better to get a second high efficiency boiler for the radiant floor system?

We also have a domestic water heater but I don't think it is a good idea to tie into this system.

EBEBRATT-Ed

Use the existing. You already have a condensing boiler why buy another? It could well be oversized, but I would use it until it needs replacement.

Adding the radiant zone will have to be done by someone that knows what they are doing.

In addition, depending on how the old system is piped you may have difficulty separating the first floor from the second floor that would make what you want to do no feasible

EdTheHeaterMan

Someone that knows how to install radiant floor heating systems should have no problem getting your system to have two different supply temperatures from that boiler. You should actually have that boiler working on outdoor reset for the cast iron radiators to get the most out of that WM. There is a great mixing valve that you can use to get the lower temperature zone to also be on outdoor reset.   If that boiler is oversized for the home as it currently is, then you don't want to add more BTU’s to your “SYSTEM” with an extra boiler.    (I use System as the entire home’s HVAC equipment)

Take a look at this information

available on page 24 of this text book I used when teaching a one day seminar for the EH-CC.org.

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference%20Guide.pdf

HVACNUT

Its a 400K input modulating condensing boiler, extremely high water volume by the looks. Staple up will not take the place of CI radiators, so stage it, do not eliminate it.

Definitely use the existing boiler, but hire an installer who will follow the WM manual to pipe it, and set up a seperate Circuit for the radiant in the U-Control. I can't see enough of the piping to see if it's correct, but what I can see looks a little funky. Like the big air vent on the return. The piping at the red circulator.

Is this DIY?

pedmec

If it was me i would spend the money your gonna save from not purchasing a second boiler and get rid of the asbestos in that area. That way you can cut out the existing piping at a point where you can reconnect it to the boiler. And you can install your radiant manifold in a clean environment. Right now it looks messy because they connected everything after the gate valves, trying not to disturb the asbestos. To do a clean radiant manifold your going to need a wall to hang it on to install it neatly. By having a clean wall to work on will save some money in labor trying to work around all that piping. then again its might be my mechanical OCD.

EdTheHeaterMan

You can use outdoor reset on the CI radiators using the boiler ODR setup. You can then use this https://www.tacocomfort.com/documents/FileLibrary/101-089.pdf to reset the lower cast iron reset temperature to an even lower reset temperature for the floor heat.   “Reset the reset”

@HVACNUT has a good idea with keeping the CI radiators and just heat them when the floor is not enough on very cold days. If the first floor renovations call for removing the cast iron, perhaps you can relocate them and perhaps eliminate only one of two. Or perhaps use some panel radiators on a separate zone that can be staged for when the floor is not able to keep up with the extreme cold  

Also that is a pretty big boiler for a 900 square foot 2 bedroom rancher.

ryanjj2

Thanks all.

@HVACNUT my project won't be a diy. I wouldn't know how to tie into the system. the old system used to be fed by coal in the 1800s so maybe that accounts for the piping?

@EdTheHeaterMan thanks for the suggestions. has been hard to find someone in my area with good ideas that don't cost a fortune. most people just want to put in a ducted system but we really want to use our hydronic system (and it is a big boiler - supplies about 3000 sq ft)

EdTheHeaterMan

Another idea for you: if you already have a duct system for you central air conditioner, you can add a hot water duct coil to the ductwork and with a few relays, you can use the ductwork as the additional heat for times when the floor heat is not sufficient. That is what is in my son's home right now. Some radiant floor heat and some hot water duct coils in the AC Duct Work. I have made some wiring diagrams for folks herein that have a setup just like that.

hot_rod

A simple piping for two temperatures. Boiler to a separator, mix valve and high temperature load off sep.

This gives you air, dirt, magnetic and hydraulic separation. Provides adequate flow for the boiler. Clean up all that near boiler piping.

Seems like a lot of pump for the radiators?

If the boiler runs on ODR, and it should, and you have just one zone of radiant, use a manual 3 way mix valve. It's temperature moves along with the reset temperature.

The discolored PVC vent is a giveaway that the boiler runs hot. Flue gas temperature beyond PVC rating, no doubt :)

Screenshot 2024-12-01 at 6.52.18 PM.png

Kaos

I think you might win the oversizing record. You have 100BTU/sqft boiler capacity, that is enough output to heat a barn with open doors.

No need for another boiler, as others have said, it is relatively straight forward to tie into the exiting setup.

When removing rads, I have also had good luck with Ultra Fin. These can be configured to run at the same temps as your existing rads, so no need for low temperature zones.