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Green Basics

Hydronic Systems

UPDATED on April 18, 2014Hydronic Systems Circulate Hot Water

ABOUT HYDRONIC SYSTEMS Heat, but no ducts for air conditioning Hydronic heating systems distribute heat by pumping water or a solution of water and antifreeze through tubing made from copper or a type of plastic called cross-linked polyethylene (PEX). Most systems rely on a boiler to heat the fluid. They typically burn fossil fuels, such as natural gas, heating oil, or propane. Dual-fuel boilers can burn either one of two fuels, cordwood or fuel oil, for example. Other appliances are sometimes used to provide hot water, such as a heat pump, water heater, or solar collectors (see More About Hydronic Systems below). Hydronic heating systems can include baseboard radiators, wall or ceiling panels, in-floor radiant tubing, fan-coil units, or a combination of two or three of these. Baseboard and free-standing radiators need relatively hot water — 160° F or higher — to operate while radiant-floor systems can heat a house with much cooler water temperatures. Hydronic heating systems are clean and quiet Because hydronic heat does not rely on the circulation of air, it does not move dust and other contaminants around the house. Most hydronic systems don’t use fans, either, so they don’t make much noise and they don’t create drafts. The pressure imbalances that forced-air systems can inadvertently create are not a problem with hydronic systems. The big drawback with a hot-water heating system is that it’s limited to providing heat. Unlike a forced-air system, it doesn’t have ductwork that also can be used for mechanical ventilation, air filtration, central dehumidification, or (in most climates) air conditioning. If homeowners want an air conditioning system, it will have to be added separately. In-floor radiant heat is unobtrusive Radiant-floor heat usually relies on loops of plastic tubing embedded in the floor. (Some in-floor radiant systems use electric resistance coils embedded…

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  1. kurtz | | #1

    Pump selection
    Could someone point me to any literature dealing with selection of pumps? I am specifically trying to find out thoughts on saving money doing one pump instead of two. One larger one that might do double duty circulating water through an open loop solar thermal system(40 feet up to the roof) during the day and then dumping the heat into my pre-plumbed radiant slab (basement(400sf) main floor(1000sf) and master bath(150sf). Water pressure would be enough for preheating for domestic use. Thanks for any help! Great site! Cant wait to keep reading!-dk

  2. GBA Editor
    Martin Holladay | | #2

    Sizing hydronic circulators
    Here are three resources for sizing hydronic circulators:

    1. A good book is:
    Modern Hydronic Heating for Residential and Light Commercial Buildings, by John Siegenthaler. Cengage Learning, 2003. ISBN #0766816370.

    2. Here's an online guide: "Sizing Circulators for Hot Water Heating Systems."

    3. "Hydronic Heating and Hot Water Recirc Systems," a handbook published by Grudfos, a manufacturer of circulators, is available online.


    Pump charts
    I've found the pump charts in the Grainger catalogue to be useful in sizing Taco pumps for these sorts of applications. With 40 feet to the roof you are looking at a Taco 009 or larger. But the floor loops would probably be served by an 006 which would likely be less expensive than the three-way valve you would need to divert the flow from the solar harvesting circuit to the radiant heating circuit, so the savings of using a single pump would likely not materialize.

    Recently I've been getting some very energy-efficient French pumps from Solar H2ot in Cary, NC, and they have an engineer there, Dan Gretch, 919-656-9810, who is very helpful on phone support and pump sizing and pipe design.

  4. GARY H | | #4

    How to get ALL the facts about radiant heat and other uesfull
    The publication used by the design Engineering HVAC professional WORLD can now be yours FREE.
    SO why not get the facts as published around the world rather than listen to billybob?

  5. MIke | | #5

    Electric or gas hydronic in floor heating
    I am building a new home on the water about 2800 SQft with 12 ft vaulted cieling over the living and kitchen area. My lower floor area is foam block foundation. I am trying to figure out if gas is better or electric hydronic in floor for heating. I am considering the gas unit that will do both the floor heating and hot water. an un bias opion would be helpful

  6. GBA Editor
    MIKE GUERTIN | | #6

    P&M Link
    Gary H's post included an incorrect link. I think it should have been to Plumbing and Mechanical magazine:

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