Heat Recovery Potential from Domestic Boilers & Ovens

[Nandomech]

Hi guys, I am currently exploring dissertation ideas and have been looking into the heat recovery potential from domestic gas boilers and ovens. More specifically, I am seeing if it is viable to collect heat from these appliances during or after their use, and then pump this heat into the attic of your standard UK home. The purpose of this would be to warm up the attic space, therefore increasing the temperature in the attic, and thus decreasing the temperature difference between the attic and the rooms below it. Hence, decreasing the overall heat transfer between these areas, which would lead to a more insulated home. I made a quick sketch of the concept to illustrate this mechanism (apologies for the quality as it was done rather hastily on the train ride home) https://imgur.com/a/HE4Fmpt.

So, essentially what the above sketch depicts is a mechanism which utilizes the heat from the oven and the boiler flue gasses and runs them through a heat exchanger to warm up the ambient cold air coming into the attic.

I was hoping to get some feedback from you guys on; how viable this concept is, the variables I need to account for when trying to construct this system and also any suggestions on areas of research I could pursue to enhance my knowledge of heat recovery systems.

All advice and suggestions are welcomed and greatly appreciated.

 

[russ_watters]

Hi guys, I am currently exploring dissertation ideas and have been looking into the heat recovery potential from domestic gas boilers and ovens. More specifically, I am seeing if it is viable to collect heat from these appliances during or after their use, and then pump this heat into the attic of your standard UK home. The purpose of this would be to warm up the attic space, therefore increasing the temperature in the attic, and thus decreasing the temperature difference between the attic and the rooms below it. Hence, decreasing the overall heat transfer between these areas, which would lead to a more insulated home.

"Insulated" doesn't mean warmer, it means that heat flow is blocked by a physical barrier. Heating the attic doesn't increase insulation.

Ovens already dump all of their heat into your house, so they already are "recovering" it to warm your house.

When you say "domestic gas boiler" are you talking about a heating boiler or is that a Britishese word for a tap water heater? Most of the heat from/for tapwater already goes into your house, and a heating boiler is already heating your house, of course. I guess though if they are gas fired and not already equipped with heat recovery, the exhaust gases are hot and some of that heat can be recovered. Generally, such appliances are about 80% efficient and you can recover about 15% of the wasted 20% with a heat exchanger that warms up the combustion supply air.

I made a quick sketch of the concept to illustrate this mechanism (apologies for the quality as it was done rather hastily on the train ride home) https://imgur.com/a/HE4Fmpt.

Ovens don't have combustion exhaust vents; they exhaust their combustion products directly into your house. Also, water heaters/boilers don't exhaust into your attic, but like I said, you could use a heat exchanger sort of like how you drew it.

...to warm up the ambient cold air coming into the attic.

Air shouldn't be forced-circulated through an attic. The boiler/water heater needs fresh air for the burner though, and you can use the waste heat to warm that up.

...and also any suggestions on areas of research I could pursue to enhance my knowledge of heat recovery systems.

The name of these systems is "condensing boiler" or water heater. Google those terms and read-up on some products and resources you find on heir principles of operation.

 

[Rive]

If you have waste heat at hand then instead of using it to warm up some space you does not live in you should use it directly to warm up the house.
The best choice on this waste heat line is to use it to warm up the cold, fresh air from outside through a heat exchanger and just keep the heat inside.

Ps.: regarding the attic the best choice is to insulate it well that it remains cold...

 

[jrmichler]

This photo shows the roof over a poorly insulated attic. The heat lost from the inside melts snow, which freezes when it gets to the cold edge and causes ice dams and icicles. The bare roof is an area where the snow slid off (metal roof). The building manager says that they added ceiling insulation two years ago. They clearly did not seal ceiling air leaks. Air leaks can cause more heat loss than lack of insulation.

This photo shows a roof over a well insulated, and well air sealed, attic. Minimal heat loss equals no melting equals no ice dams or icicles. Also low heating bills, no drafts, and no cold areas in the house.

Allowing warm humid air to flow into a cold attic causes the moisture in the air to condense on the underside of the roof. When temperatures rise in the spring, the frost melts and causes water damage inside the house. A local builder learned this the hard way and I made some money pointing it out. A friend also learned this after he fixed the kitchen exhaust fan and inadvertently created an air leak into the attic. Fortunately, we found the problem before the mold rotted out the roof.