Savings

Steve Ebels_3

And look at the "Viessmann vs Furnace" post regarding a forced air to hydronic conversion. This was a 13,000+ sq ft building, mainly cement block with decent windows but minimal insulation. The huge difference in energy costs are attributable to the following in descending order.

1. Zoning

2. Duct loss

3. Equipment combustion efficiency

4. Electrical consumption

I'm guessing here but a gut level estimation of the percentage of savings for each would be 15%, 12%, 10% and 6% respectively.

Nick_16

Savings

Everyone knows that according to physics, it takes fewer BTU's to heat water than to heat gases (air). This is a simple concept, however, how much difference is there? How much money would be saved if a person say, converted there home from a 80% gas forced air furnace to a 80% boiler w/baseboard (baseboard not radiant because radiant and convective heat loss if different). How much cheaper is it to heat water than air?

Al Letellier

air vs. water

In my book, a comparison like this is not about difference in BTU input to heat the house...it's more about comfort, and hot water beats air anytime, in my humble opinion. With air, it looses heat a lot faster that hot water in a length of fin tube or a radiator.

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Andrew Hagen (ALH)

Control Volume

Given the same heat load and combustion efficiency, theoretically there should be no difference.

What goes in must come out. Look at where it's coming in and where it's leaving. Fuel comes in. Where does it leave? Is it out the flue or is it heat loss?

-Andrew

jerry scharf_3

huh?

John,

Your first sentence makes no sense to me, but it may be because I did't go far enough in my physics training (got my degree and wandered off into computers.) Water or air are transport media to move heat from where you generate it to where you want it. You can add BTUs to both, and you can move both. It is generally accepted that water is more effective that air, but the details of the install are critical. A botched hot water install can be less efficient that an excellent air install. The best water installs (not what you assumed) are much superior to any air based system I know of.

In an ideal transport model, it will take more energy to move the BTUs on top of air than it will with water. Also, since the surface area of a duct is greater than a pipe, you will get more distribution loss. A big piece is that as systems go less than ideal, almost all water systems are sealed whereas duct systems often leak. This leakage can kill the efficiency of the system.

You chose baseboard for comparison, which is a less efficient system. Because a large part of human comfort is related to the mean radiant temperature, using heated air to heat the walls is the least efficient way to do this. Panel radiators are significantly better and radiant speaks for itself. In these cases, the heat converted to radiation will generate more human comfort and less heat loss through the envelope than doing it by heating air.

As for how much, it is approaching an absurd question. No mention made of control strategy or house to be heated. Beyond that, even in a pair of identical houses, the execution details will swamp any prediction based on engineering generalities.

jerry

DanHolohan

See how valuable it is

having it in On the Job? ;-) Thanks again, Steve.