New design---piping questions

dave123

I'm still roughly sketching in my head how a retrofit hot water system would work in my 1950s house. Heat loss analysis per the Siegenthaler method gives 44K on design days. House is a raised ranch with 1800 SF on main floor, and below is half walk-out basement, and also a 750 SF unheated garage. Plan is to install 12 radiators on the main floor.

I understand the advantages of home run pipes in this situation, but because of the layout of the house, it would require running at least 10 pipes across the ceiling of the unheated garage. Even with insulation on the pipes, this seems like a lot of unwanted heat loss to the garage. So then would a parallel-direct return, utilizing just two (larger) pipes, make more sense for those radiators above the garage?

If so, should the rest of the radiators, those above the heated basement, also be direct return, or would it be better to home run them? It seems to me there might be an advantage, when it comes to balancing, to have the whole system piped the same.

Thanks.

hot_rod

it depends somewhat on how you want to zone or control the radiators?

If you series radiators keep in mind temperature drop.

dave123

I was thinking putting all the rooms above the garage on one zone, since their heat loss is different from the rooms above the heated basement. So one zone for above garage, and one zone for above basement, each radiator with a TRV.

hot_rod

what about the main living area, is there one?

dave123

It is over the basement. Two bedrooms and both bathrooms are over the garage.

hot_rod

cast iron radiators? if so they should be sized to the individual room loads. If not I would add a TRV on each so you have room by room control, or at least a manual valve so you can balance them.

The home run gives you the most options, each radiator could be zoned with a wall thermostat, connected to an actuator on the manifold. Or with a TRV on each radiator, eliminating the need for wiring. I like bedrooms to have individual control, if they can be closed off from one another. Use a delta P circulator to track best with a zoned distribution.

With that small load, 3/4" could pipe all radiators together with reverse return to balance flows. One loop for each area of the house.

It depends on how much individual control you want, either now or in the future.

Often a bunch of tubes can be bundled together and insulated as one to cross the garage for example.

dave123

But it sounds as though there's nothing inherently wrong with piping one half with direct return and the other with home runs?

hot_rod

Not to to overwhelm you with options, but here is a journal we publish with various piping ideas, pros and cons.

Anything with an X through it is a mis-interpretation of a piping concept. Best not to use one of those

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_19_na.pdf