Size pump and heat exchanger for future loads or current loads (hydronic radiant)?

davidd

Hello,

I am adding a small snowmelt system to a pre-existing boiler, hydronic air, and indirect water heater system. The snowmelt will be on its own closed loop, with a heat exchanger, glycol, pump, and zone valves. I may add another section of snowmelt in the future. I also plan to add underfloor heat to a couple rooms. Because of where the rooms are located, I'll be using glycol for the underfloor heat too.

Would you size the pump and heat exchanger for each project (separate pump and heat exchanger for each subsystem), or size based on what is planned for end state (bigger pump and bigger heat exchanger)?

Approximate sizes here are:

- Snowmelt 1 = 200 square feet (what is being installed first)
- Snowmelt 2 = 900 square feet
- Underfloor 1 = 100 square feet
- Underfloor 2 = 150 square feet

The snowmelt area's won't be idled. They'll only be active when needed to melt snow.

I'm thinking I can save time and money by having one closed loop (in addition to my non-glycol closed loop) instead of multiple. I haven't done any math to determine sizing of the pump or heat exchanger yet.

None of these are critical zones. If I use one pump and it fails, and all of these are out of commission, it will be a nuisance, not a life threatening situation. In other words, the benefit of not having all my eggs in one basket isn't worth much to me, in this particular situation.

The heat load will be significantly more for the snowmelt areas than the underfloor areas, both because they are larger and because the btu requirement per square foot is a lot more. I'm not sure if a heat exchanger sized for all 4 areas will cause some sort of problem when only the underfloor areas are active.

I plan on using a variable speed ECM pump.

Thanks,
David