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Help needed with manifold design

Wade87 Member Posts: 1
Hello, I’m a first-time poster but I have spent some time reading this forum and I greatly appreciate the depth of knowledge and willingness to help newbies that I’ve seen here. I would like some advice on how best to proceed with a home heating project that I’ve been working on for some time.

I would like to install a closed-loop hot water system as the primary heating source in my home. I have this in another property and it works wonderfully. My house is two levels plus a basement, roughly 20’ x 20’ per floor. The main floor consists of a living room @ 200 sq ft, dining room @ 100 sq ft, and kitchen @100 sq ft. The second floor consists of a main bedroom at 170 sq ft, a guest bedroom at 125 sq ft, and a bathroom at 60 sq ft, plus hallway.

The current heating is via a forced air furnace installed in 2018. It works well but my natural gas costs have risen dramatically compared to the old model.

I would like to have independent zone control with three separate zones, (1) being the entire main floor, (2) being the main bedroom and bathroom, and (3) being the guest bedroom. I assume this will require three separate pumps, one for each zone, with a miniature manifold feeding the loops in each zone. I’ve had to replace a pump at my other property, so having some flexibility / elasticity in the manifold design is very important to me, as I assume I will eventually need to replace a pump here.

For a heat source, I would like to use an instant-on natural gas hot water device. My reasons for choosing this are to minimize the size of the installation and eliminate the complexity of having a 40-gallon water heater. Are there reasons I should consider a normal hot water heater instead? One major attraction of the instant option is that it burns outside air, which should improve the overall efficiency of the house.

What should I do for thermostat control? I would like a basic programmable thermostat for the main floor so it can be warmer during the day than at night, and a programmable option for the main bedroom and bathroom so it is warm evening through morning. The guest room doesn’t need to be heated most of the year and would be fine with a non-programmable thermostat. Do you have any recommendations on models or options, and suggestions on what factors I might be overlooking? And do you have any recommendations for manufacturers to buy or ones to stay away from?

Do you have any other suggestions on how I should lay out the manifold?


  • Jamie Hall
    Jamie Hall Member Posts: 22,112
    Before I get to the manifold...

    Please don't use a hot water heater, instant on or otherwise, as a heating boiler. They're not meant for the job and they will live a short, expensive, and miserable life. Do a heat loss calculation for the house -- Slant/Fin has an excellent little app for the purpose -- and get a proper mod/con boiler sized for the heat loss. There are a number of good makes. Run it with outdoor reset, and save much money.

    Now... piping. Assuming you do get yourself a nice mod/con, it will have its own pump. This is used to circulate water through a "primary" loop, which includes a manifold -- and its running, if properly set up, almost all the time providing water which is just hot enough to keep the building where you want it to be. Then each of your zones would have their own pump taking water from the manifold, running it through the zone, and returning it to the same manifold, but downstream of where the takeoffs are. These pumps, too, are running most of the time, but they can be controlled by a thermostat for each zone.

    Look up "primary/secondary" piping...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,493
    What type of radiator are you planning to install?
    It sounds like you would be better off with a combi boiler. You might take a look at a high mass unit like the HTP Pioneer considering your desire for microzones.
    I would consider using a single pump for the zone side and then using zone valves that will thread onto a manifold.
    Have you done a heat loss calc?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein