How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manufactured and modular homes

How does a hydronic heating system work?

Saturday, August 18, 2018

The principle of hydronic heat is simple. A hot liquid, usually water, is circulated continuously through piping to transfer heat to the air of a home. A sophisticated system that utilizes zig-zag loops of plastic tubing running under the floor to make the floor surface itself into a radiant heating panel is used in colder climates than ours. Also, old-fashioned radiators and baseboard heaters are an earlier version of hydronic heat technology.

   But the type that we have in our North Central Florida area utilizes the hot water created in the home’s water heater. It is piped into a cluster of finned pipes in a box placed above, or as integral part of, an air conditioning air handler (indoor unit) and in-line with the air flow into the ducts and registers around the home. An electronic solenoid valve opens when the thermostat requests heat to start the flow of hot water to heat the piping and warm the air flow.

   Here’s how one manufacturer describes the system: 

“Water from your hot water source is circulated through the coil unit while the central air system blows air through it. The air temperature is raised by 30˚ to 60˚ F while the water’s temperature is lowered about 15˚ to 30˚ F. The warmed air is delivered to your home and the water is returned to the source to be reheated.”

   Because the water is recirculated, the system does not increase water usage. The water heater is typically natural gas and a larger unit than normally required for a home without a hydronic heating system.

• • • • • • • • • • • • • • • • • • • • • • • • • • • • 

  To learn more about heating and air conditioning systems, see these other blog posts:

How can I find out the SEER of my air conditioner? 

My air conditioner won't turn on. What's wrong? 

How can I find out the size of my air conditioner? 

How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

Where is the air filter for my central air conditioner and furnace? I can’t find it? 

Does an old air conditioner use more electricity as it ages? 

How did homes stay cool in Florida before air conditioning? 

What is wrong with an air conditioner when the air flow out of the vents is low?

Why has the thermostat screen gone blank? 

Why does it take so long to cool a house when an air conditioner has been off for a while? 

Why is my air conditioner not cooling enough? 

What are the most common problems with wall/window air conditioners?  

Will closing doors reduce my heating and cooling costs? 

   Visit our WATER HEATERS and HEATING AND AIR CONDITIONING pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

Water Heaters

Water Heater Age

"What Are The

Signs Of..."

Septic Tank Systems

Structure and Rooms

Plumbing Pipes

Termites, Wood Rot

& Pests



When It First

Became Code

"Should I Buy A..."

Park Model Homes


Shingle Roofs




Wind Mitigation

Roof and Attic

"Does A Home


Pool and Spa

"What Is The Difference Between..."




Concrete and

Concrete Block

Metal Roofs


Modular Homes

Rain Gutters

Mold, Lead & Other Contaminants


Older and

Historic Houses

Crawl Spaces

Mobile-Manufactured Homes

Building Permits

Life Expectancy

Clay Soil





Exterior Walls

& Structures


Common Problems

HUD-Code for

Mobile Homes

Garages and Carports

Flat (Low Slope) Roofs

Electrical Panels

Sprinkler Systems

Electrical Receptacle Outlets

4-Point Inspections

Hurricane Resistance

Frequently Asked Questions (FAQ)

Home Inspection

Heating and Air Conditioning

Building Codes

Fireplaces and Chimneys

Inspector Licensing

& Standards

Energy Efficiency

Washers and Dryers



Doors and Windows



Electrical Wiring

Click Below  

for Links

to Collections

of Blog Posts

by Subject

Plumbing Drains

and Traps


Smoke & CO Alarms

Aging in Place

Top 5 results given instantly.

Click on magnifying glass

for all search results.






Air Conditioner & Furnace Age/Size


Electrical Switches





Water Intrusion

Electrical - Old

and Obsolete


Foundation Certifications

Tiny Houses

About McGarry and Madsen



Buying a home in North/Central Florida? Check our price for a  team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.

Moisture Problems

Crawl Spaces