Straw Hall Hydronics

The BBHSP community meeting space is called “Straw Hall” because it has walls and insulation partially made from rice straw. The floor is made from very thick NHL (Natural Hydraulic Lime Plaster), and includes insulating layering, structural rebar, and a network of Pex pipe for the hydronic radiant floor heating system. We plan to connect the system’s heat-exchanger to a geothermal source, but for now, the systems operates using it’s “back-up” heat source: a tankless propane water heater (AKA “boiler”). This web page is intended to store information about the hydronic in-floor heating system, as we work out the bugs and improve its functionality and efficiency.

The water heater boiler unit is a propane Noritz Always Hot Model NC1991-DVC.

Exterior Vent Pipe Clearance Issue:

The exterior vent pipe termination outlet from the boiler is just over two feet clearance (2′ 2.5″) from the soffit venting above the termination. **What amount of clearance does the boiler’s manual and relevant building codes call for?

**Building Inspector wrote: “WH (Water Heater) exhaust within 2 feet of eave vents. Consult Install Guide, as needed”


Question: Is the current configuration acceptable, and if not, what is the best way to remedy this issue? Some possible answers:

A. Some Options to Consider:Shorten interior vertical vent section and move horizontal section lower on wall. (Requires making new hole in plaster and wall and then patching old hole). Questions: Is a shorter vertical run OK for interior vent pipe? Is this the easiest way to solve problem?

B. Extend horizontal section of vent pipe that goes through wall so that it extends past soffit and vents out further away from building. Questions: would it need bracing from roof edge (or wall), and does code allow this kind of arrangement?

C. Extend vent pipe on exterior by adding three more 90ยบ elbows and running pipe along soffit, out past roof edge.

D. Replace propane-powered boiler with electric tankless water heater. Question: would electric water heater also require venting to outside?

Other Concerns and Questions:
Increasing Effectiveness of Room Heating: Floor (made of Natural Hydraulic Lime) is so thick that pipes are not near surface, and the floor is not heating up very well with standard settings on boiler and pumps. Can the water heater be turned up to solve this problem, so working fluid running through floor pipes is hotter?

Can this Remote Controller (below) be turned up? What does it do?
What is the maximum setting?

Also… What does this controller do (below), and can it be turned up to make circulating fluid (and the floor) hotter?

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