Flue recapture

Steve Ebels_3

Anything that pulls heat from the flue, by any means, is lowering the flue temp. Doesn't matter if it's a device working directly in the flue or external to it such as you proposed. What you're up against is the simple rules of physics as they apply to non condensing, atmospheric draft equipment. It's designed to work within a given set of parameters and there's plenty of trouble if you cross the line.

fsk

Flue recapture

I see lot of smart discussions on the board abut heat calculation etc...
Just a thought.
I have an oil burner and I have the flue ocoming out of the burner and going into the chimney.This flue is kind of 2 feet away from the chimney.
I was wondering if I can some how get some heat from the flue back into the heating area.Silly it may sound but inputs will be interesting to read..
Let me know..thank you.

Paul Fredricks_3

There have been various devices over the years to recapture some of the heat before it goes up the chimney. Most have utilized a box with tubes that run perpendicular to the flue pipe. The flue gases travel over the pipes and a small blower pushes air through the tubes. The heated air is blown out into the room. These units might have a rod attached to a plate inside that could be dragged back and forth to clean off the inside of the tubes when soot accumulates.

The main issue can be that with modern equipment the flue temperature is already fairly low. If more heat is removed, condensation can occur in the chimney causing a host of problems. The unit also has to be properly supported so that it doesn't break the flue pipe fittings causing a potential health disaster in the house.

It is possible that these units aren't allowed by code, but you would have to check with the local building authority.

Steve Ebels_3

I'll tell you why you shouldn't

Last year I took a call from a customer who wanted a new boiler installed. February. Not a time you would pick. I went to his house equipped with a couple emergency heaters and found the following. The guy is an engineer in a manufacturing plant near here and is a sharp cookie. Three years before my visit, he had measured the flue temp of his gas boiler and found he had 430* air going up the stack. He promptly went out and bought a Magic Heat and installed it in the flue of his two stage Hydrotherm. Fast forward to February. A large piece of drywall falling off their bedroom ceiling had alerted them to the fact that they had a very severe flue gas leak allowing condensation to form in the stud space where the chimney ran and from there into all parts of the first floor ceiling. There was black mold everywhere and they wound up gutting that entire part of the home and sanitizing. What happened was that the Magic Heat worked as advertised and robbed heat from the flue gas. This allowed condensation to form in the B-vent which eventually ate through and leaked flue gas into the house. His wife had been having unexplained headaches for over a year. CO poisoning anyone? No headaches since the new boiler, HHMmmmmmmmmm.........You don't suppose.........

Regardless of whether you have a brick or metal chimney, you need to maintain a minimum flue gas temp lest you can buy yourself a whoooooole lot of trouble.

fsk

I am not looking at installing a magic heater etc.
I was thinking of raping smoe metal condutors around the lfue,at least they will heat up and heat the air that ocmes in their ocntact.

Overall was looking for way to increae the heated surface area..by attching things aorund the flue..is that a good idea..
Please advise the down side...

realolman

Anything

that you do to extract heat from the gasses going up your chimney will lower the temperature of them. One of the products of combustion is water vapor. If you lower the temperature of the flue gas enough, the water vapor will condense out of them as a liquid which is corrosive enough to eat up your smoke pipe and your masonry chimney. Also it may screw up your draft and allow carbon monoxide into your house.

It really does seem like something that you could do, but it's so obvious I suppose everything has been tried.

They make boilers that are made specifically to condense out the water and capture most of that heat that you're losing up the chimney. That's what you should look into if you really want to capture the heat.

Home Depot Employee_2

ditto

Assuming you raise the temp of your basement 1/4 of a degree, is it worth the risk?

Paul Fredricks_3

I remember these accordion looking bands they used to put around the flue pipe to take heat off. They did nothing but get in the way during the cleaning.