Attic Heat Harvester
attic heat harvesting controller, 1 floor


Attic Heat Harvester Controller System

Frequently Asked Questions

What does 'efficiency' mean?
Why is the Attic Heat Harvester System so much more efficient than any other home heating system?
Why is the Attic Heat Harvester System so much more efficient than systems that use heat pumps?
How efficient is the Attic Heat Harvester System?
How does the location of my home impact the Attic Heat Harvester System efficiency?
What does the Attic Heat Harvester System comprise of?
using heat in hot air - buy now When does the Attic Heat Harvester System produce the maximum heat energy
Can I change the Attic Heat Harvester System's efficiency?
Should I buy an Attic Heat Harvester System?
What factors should I consider before deciding to buy an Attic Heat Harvester System?
What is the pay back time for an Attic Heat Harvesting System?
How easy is the Attic Heat Harvester System to install?
How much will the Attic Heat Harvester System cost to install?
Can I install an Attic Heat Harvester System?
Where is the most effective area of my home to use an Attic heat Harvester System?
How much will the Attic Heat Harvesting System reduce my annual energy costs?
What is 'supplemental heating'?

Q. What does 'efficiency' mean?

In this web site we consider efficiency in terms of the relative cost per unit (kWh) of heat energy.

Efficiency is calculated as: 'value of the heat produced by the heating system' / 'total cost of the source of heat'.

In our efficiency calculations we assume that heat provided by electricity is 100% efficient. Additionally we have used the US average cost of electricity. More information on the costs of different heat sources in the UK can be found here.

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Q. Why is the Attic Heat Harvester System so much more efficient than any other home heating system?

The system is so much more efficient than other home heating systems because most of the heat is free as it comes from the sun. In comparison with all other home heating systems only a very small amount of electrical energy - typically 60 to 90 watts, is needed to move the heat from the attic into the home. The controller power consumption is typically no more than 2 watts.

Almost all other home heating systems use electricity to control them (even when they are not in use i.e. in standby mode), and to distribute the heat around the home. The cost of this electricity is seldom if ever stated in sales documentation except for heat pump based systems which use a lot. In reality the Attic heat harvester system uses far less electricity to operate than is used by other systems in standby mode.

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Q. Why is the Attic Heat Harvester System so much more efficient than systems that use heat pumps?

Heat pumps generally extract heat from the ground - ground source, or from the air - air source.

Heat pumps use a significant amount of energy to get the heat into your home, far far more than is used by the attic heat harvester system. Compared with the attic heat harvester system the technology used in Heat pumps systems is relatively complex.

Additionally the temperature difference between the heat pump heat source and the home is generally far less than the temperature difference between your attic and your home, this also reduces the comparative heat pump system efficiency.

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Q. How efficient is the Attic Heat Harvester System?

The attic heat harvester system efficiency is dependant on you homes characteristics and location. System efficiency is directly proportional to the 'attic - room' temperature difference and on the air flow rate achieved as shown in the following chart.

graph showing the efficiences of various heating systems

Modern gas, oil, wood, coal and electric central heating systems can achieve efficiencies of from 0.25 to 1, the efficiency of old systems is less. Modern heat pump based systems can achieve an efficiency of 3.

At a typical air flow rate of 1500cmh and a modest attic - room temperature difference of 5°C the attic heat harvester system is 34, at 10° it is 68!

In common with all systems that use solar energy or systems that use heat pumps the attic heat harvester system efficiency varies depending on your location - especially latitude. The attic heat harvester system efficiency is proportional to the temperature difference between the hot attic air and the area being heated by the hot air.

If you use the system kit we supply and follow the installation instructions system efficiency is given by:

Efficiency = 3 * the temperature difference between the attic duct inlet and the area being heated.

The attic heat harvester system efficiency is proportional to the temperature difference between the hot attic air and the area being heated by the hot air.

If you use the system kit we supply and follow the installation instructions system efficiency is given by:

Efficiency = 5.4 * the temperature difference between the attic duct inlet and the area being heated.

An attic heat harvester system efficiency is affected by:

a) how much sun your attic roof receives during the period of the year that your home needs heat.

b) how warm you like your room - heating cool rooms is more efficient that heating warm rooms.

c) the value of the Attic Heat Harvester Controller 'Attic - Room temperature difference' parameter affects system efficiency, the higher the value the greater the system efficiency.

d) The difference between day and night time temperatures, if nights are cold your home cools down and will need heat during the day.

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Q. How does the location of my home impact the Attic Heat Harvester System efficiency?

The latitude of your home impacts the amount and strength of the suns rays, the closer you are to the equator the stronger the suns rays.

The height of your home above sea level affects how cold the nights can be, the attic heat harvester system works best where nights are cold.

The number of rainy days you get during the time that your home needs heat impact your attic - room temperature difference and hence the efficiency of an attic heat harvesting system.

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Q. What does the Attic Heat Harvester Controller System comprise of?

The attic heat harvester system essentially comprises of:

a) a Attic Heat Harvester Controller

b) a compatible temperature sensor with a short cable for the room temperature sensor

c) a compatible temperature sensor with a 25ft cable for the attic temperature sensor

d) a twelve inch fan unit

e) one or two motorized air valves dependant on whether you need the attic cooling option

f) a length of flexible 12 in duct - systems are generally supplied with a 25ft length

g) some two wire with ground cable and some low current 3 wire cable for the air valve motors

h) a fused electrical switch unit

Attic Heat Harvester Ltd. can supply items a) thru f) as a kit.

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Q. When does the Attic Heat Harvester System produce the maximum heat energy

This depends on when the sun shines, where the sun is in the sky, the orientation of your attic roof with respect to the sun, and on the construction of your attic roof.

Many homes have roofs where plywood or OSB sheets are fixed to the roof trusses. Shingles, tiles or perhaps slates are mounted on the flat sheets, these slow the heat transfer to the attic. However they also retain heat as the sun dips to the west. Typically the effect of this is that maximum heat is delayed by a few hours as can be seen on the temperature charts on this web site.

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Q. Can I change the Attic Heat Harvester System's efficiency?

See the question above 'How efficient is the Attic Heat Harvester system'

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Q. Should I buy an Attic Heat Harvester System?

a) If you have an attic with a roof that the sun shines on or partially shines on and your home needs heat at some periods of the year an attic heat harvester system can reduce your heating costs because it is far more efficient than any other home heating system, i.e. the heat costs far less.

b) if you are concerned about climate change and want to minimize your impact on the environment by using free solar energy there is no more efficient system than an attic heat harvester system.

c) if your motivation is to save money, consider the size of your annual heating bill - if this is small your annual savings are likely to be small.

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Q. What factors should I consider before deciding to buy an Attic Heat Harvester System?

The attic heat harvester system relies on attic temperatures being higher than room temperatures. Home temperatures were monitored from May through August 2011 near Edinburgh Scotland, not a place known for sunny days.

If you are not sure of the temperature difference between you home and your attic you could purchase an inexpensive wireless indoor and outdoor temperature monitor. Place the indoor unit in the room you wish to heat and the outdoor unit near the apex of your attic and monitor and record the temperatures.

Preliminary research for the attic heat harvester system used a La Crosse data logger. La Crosse sell an inexpensive WS9117U unit that monitors and displays the temperatures and records maximum and minimum temperatures.

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Q. Where is most effective area of my home to use an Attic Heat Harvester System?

The most effective area to use an attic heat harvester system is in the area in your home that requires the most heat. These areas are often the living areas or rooms on the non sunny side of your home or in heated basements. It is generally more effective to use attic heat to heat a low area of your home as hot air rises - a home with a heated basement needs less heat to heat the upper floors.

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Q. How much will the Attic Heat Harvester System reduce my annual energy costs?

The attic heat harvester system could save you 5 to 80% of your annual home space heating bills dependant on the location, orientation and construction of your home.

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Q. What is the pay back time for an Attic Heat Harvesting System?

The attic heat harvester system efficiency varies - see the question 'How efficient is the attic heat harvester system'.

Our experience indicates that the pay back time could be from 1 to a few years. You should also remember that the attic heat harvester system maintenance costs are minimal as the system is very simple, this reduces system pay back time. Another factor to consider in your deliberations is the positive impact of using the system on our world and on our descendants as it reduces the use of fossil fuels.

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Q. How easy is the Attic Heat Harvester System to install?

The system is relatively easy to install, see the web page Installing an attic heat harvester system.

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Q. How much will the Attic Heat Harvester System cost to install?

Typical installation costs vary somewhat but could be low $100's for a 1 floor home and higher for a 2 or more floor home dependant on how difficult it is to run a relatively straight 12 inch duct from the attic floor to the room to be heated.

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Q. Can I install an Attic Heat Harvester System?

If you are a practical person with some electrical knowledge you can install the system yourself.

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Q. What is 'supplemental heating'?

'Supplemental heating' generally refers to an additional heating system which supplements, or partially replaces your normal heating system reducing the normal heating system use but offering advantages - often reducing total annual heating cost and providing localised heat in the area where the hot air is ducted to.

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