[hn_throwaway_99]

When anyone is talking about a "100% efficient" anything, I really wish they would clearly define what the numerator and denominator are. I just looked at your site and it said "103.4% efficiency in window". Which is obviously bullshit for how most people define "efficiency".

I think it's fine if you define efficiency by some other metric where it can rise above 100%, but if so you should clearly elucidate how.

[pandora-health]

Regarding gas condensing boilers and their efficiency, the notion of them achieving over 100% efficiency, as measured by the Lower Heating Value (LHV) of the fuel, really showcases the value of recapturing latent heat. When we burn natural gas, besides generating heat, water vapor is produced as a byproduct. Traditional boilers expel this vapor and its associated latent heat through the flue, wasting a significant portion of energy. Condensing boilers, however, are designed to cool the exhaust gases to a point where the water vapor condenses back into liquid, reclaiming that latent heat. This process effectively allows the system to extract more heat from the combustion than the calorific value of the gas would suggest possible, if you only consider the LHV, which excludes the heat contained in the steam. Consequently, when this extra captured heat is added to the overall heat output, it can push the efficiency of the boiler beyond 100% using LHV calculations.

[danans]

> Regarding gas condensing boilers and their efficiency, the notion of them achieving over 100% efficiency, as measured by the Lower Heating Value (LHV) of the fuel, really showcases the value of recapturing latent heat.

At least in the US (not sure where you are), combustion boiler/furnace efficiency is required to be calculated using the HHV, which includes the heat of vaporization, not the LHV. The result is that even the highest efficiency condensing combustion heating systems all have rated efficiencies below 100%, which makes sense thermodynamically.

It seems that the standard in Europe is to instead calculate efficiency using LHV, resulting in the efficiency rating over 100% for condensing boiler. > 100% doesn't make sense thermodynamically, but is good enough for comparing when the same calculation is used.

Either way, it should be made more clear in the UI that it is using LHV.

[pandora-health]

To calculate the cost using a UK gas price we would want to have assumed an efficiency in HHV. This is because UK gas prices are given on an HHV basis. Either convention can be used as long as all of our fuel consumptions, efficiencies and energy prices are given on the same basis. Consistency is crucial.

[danans]

> This is because UK gas prices are given on an HHV basis. Either convention can be used as long as all of our fuel consumptions, efficiencies and energy prices are given on the same basis. Consistency is crucial.

If your audience is global, perhaps consider adding a toggle to switch the efficiency calculation to HHV. Think of it like the °C/°F toggle on some sites and apps.

[deegles]

Could you integrate a heat pump or solar tank pre-heater to this system and calculate how much it saves on gas? especially if you have on-demand pricing for electricity. it would be interesting to see it dynamically optimize depending on the price per BTU or some other metric.

[pandora-health]

Yes, there are hybrid heat pumps that can work with gas boilers. Such system can help to reduce gas usage by up to 70%. I am considering it :)

[infecto]

The OP was too kind to you. Most furnace efficiency ratings come from calculating the input energy and the output energy. It is pretty obvious from the site that the calculation is a simple, energy in vs energy out calculation.

Maybe you should educate yourself some before writing posts you know nothing about.

[pandora-health]

I see where you coming from and even if the simple calculation is not what it is in real life, it's definitely running more efficiently than it would otherwise. Also, there are other benefits. Mainly, climate control, which means that the room temperature is very precisely at the target level at all times, within 0.3 C degree on average. And when you have constant temperature at all times, it feels very comfortable, and you can't tell whether heating is on or off.

[hn_throwaway_99]

> Maybe you should educate yourself some before writing posts you know nothing about.

Except another commenter, obviously more versed in the field than I, specifically highlighted how this efficiency is calculated differently based on what is specified as the denominator, and the rules are apparently different for the US vs. Europe: https://news.ycombinator.com/item?id=40055464. So perhaps it is you that should educate yourself.

[infecto]

My mistake, I thought it was more common knowledge how HHV and LHV are calculate and equivalents when comparing to heat pumps. I tend to respond too harshly when low level words are thrown. Sorry!