Need help, advise for boiler rads and PEX pipe

[teddyk]

I've read quite a few posts on the site in regards to this but I guess I require more specific advice about switching my system to PEX. I like Tom Sawyers advice on a lot of the threads and hope you respond.

I have a older 2400 sqf home in Ontario, Canada, built in 1927. we've done a lot of reno's and have spray foamed 3 of the rooms while walls were open. The house has 4 finished floors which includes a finished attic with 2 rads. We just had the old boiler pulled out along with asbestos abatement. I now have a Lennox 150 BTU boiler and 2 Wilo pumps along with this 10 loop manifold.

All the steel pipe in the basement has been removed due to the abatement, I wanted them out. The steel pipe was 1 1/4" - 2". I have direct access to run pex from the manifold to all the rads in the basement and the main floor, most on individual loops. I don't see this as an issue considering they will almost all be home run. My issue is with 4 runs that go to the 2nd and 3rd floor and if I should use pex on the runs or use steel for these to make sure they get the flow they need since 3 of the 4 runs feed 2 rads each. See below.
1 run feeds a laundry room on the second floor and that's it. The steel left in the walls is 1".
2 runs each feed a bedroom on the second floor and one on the third floor and are 1 1/4" pipe in the walls.
1 run feeds a bathroom on the second floor where I have converted to a hydronic towel bar and the lines up the wall are 1 1/4"

I've been told by 2 contractors that I should go to either 1 1/4" steel or copper on a 3 loops system to supply each floor separately and that the 1/2 pex would not be sufficient to heat the 2nd and 3rd floors. However I figure since almost all will be home runs, except for the 3 that feed 2 rooms each I should be ok with just running 1/2 pex from the manifold and feeding the rads directly or tying into the 1 - 1 1/4" steel. I would also like to put the pump on the supply side as I've heard reduces air in the system. I would like to replace the 1 and 1 1/4 steel in the walls in the next few years but just need to get the heat on right now
Advice would be GREATLY appreciated, it's getting cold out and the wife is not happy with my timing on this...
Thanks

 

[teddyk]

Anyone?

 

[Sponsor]

 

[Dana]

There isn't sufficient detail here to even take a WAG at it.

The flow requirements for the radiators on the remote rooms is a function of the heat load and amount of radiation in those rooms, and the water temperature that is being delivered. With low enough heat loads and a high enough water temperature you may be able to get away with half-inch PEX, but there may be room-to-room temperature balances to tweak (there probably is some tweaking to be done anyway.)

Odds are pretty good that the boiler is more than 2x oversized (maybe even more than 3x) for your heat load at the 99% outside design temperature now that you've improved the building envelope, but the boiler sizing doesn't affect the the water temperature and flow requirements for meeting the loads. (I assume it's the GWB8-150E-2 or similar?)

If the water temp requirements at the available flow rates exceed 80C/180F for meeting the load with any of the existing radiators you can't really use PEX, since that is operating temperature limit rating for the material.

A reasonable system design would start with a Manual-J or I=B=R heat load calc for each room, along with the Equivalent Direct Radiation of the radiators in each room can get you to better than a WAG on the peak water temp requirements. Without it you are shooting in the dark.

Did you micro-zone the place with ten zone valves too (hopefully not)?

This is a real hydronic heating design problem, and "design by web forum" may not be the best approach, but the heating season is upon us.