Flue Heat Recovery

S. Orbine

With all the attention to energy costs, why do I not see any commercial heat exchangers for flue gases? I see there are patents filed, but I've never seen one for sale. Do these exist, or is there some latent problem?

ALH_4

Economizers

You mean like these? Kentube

edit: I think I missed the context of the word "commercial". ;-)

Steve Ebels_3

If I recall correctly

Both Viessmann and Buderus make a wide range of flue heat recovery devices. Neither company however has seen enough demand to warrant bringing them over here.

Aidan (UK)

Flue heat recovery

> With all the attention to energy costs, why do I

> not see any commercial heat exchangers for flue

> gases? I see there are patents filed, but I've

> never seen one for sale. Do these exist, or is

> there some latent problem?




There are two latent problems. A conventional flued boiler or stove uses the buoyancy of the hot flue gases to move the combustion products up the chimney. If you take the heat out of the flue gases, then at some point that mechanism will stop working and you will get flue gases spilling into the occupied space. Carbon monoxide is a killer.

The other latent problem is that fossil fuels (oil, gas, coal) are mostly compounds of carbon and hydrogen, with a trace of sulphur; if you burn them, you will mostly get carbon dioxide, water vapor and a bit of sulphur dioxide. Again, if you take enough heat out of the combustion products, the water vapor will condense into water. The sulphur dioxide dissolves in the water and makes sulphurous acid. This will dissolve bits of your boiler and flue, unless it is an acid-resistant condensing boiler. An unauthorized add-on like this would invalidate any boiler warranty.

There are enough liability issues there to keep any competent, sane heating contractor away from them. No DIYer would go near them, if they knew the details.

If you want to recover heat from the flue gases, the only sensible way to do it is to buy a new condensing boiler.

bill nye_3

Don't Do It

I removed this potential hazard about three weeks ago. Flue gas temperatures really should be 300°F [at least] so that the condensate does not destroy the chimney liner