17 ms·

My problem is whenever I've seen these numbers, they were completely baked. "The total price tag for the entire home project was roughly $75,000, after rebates

by blagie 3y ago

My problem is whenever I've seen these numbers, they were completely baked. "The total price tag for the entire home project was roughly $75,000, after rebates. But Tuttelman says it will pay for itself in about six years through energy cost savings." The costs seem right. I've priced this. The savings are nonsense. I don't spend $75k in utility bills in six years. "Other benefits include the stress savings of not having to guess when a furnace, which typically lasts about 15 years, is on its last legs." My boiler is going strong after forty years, and the technician who looked at it last said this was typical and there's no reason to think it won't last another forty. I periodically need to replace a control board, which I should learn to do myself. In contrast, the system described -- with heat pumps, solar, and whatnot, has a lot more parts and things to go wrong. I'm equally sceptical of the current direct environmental benefit. If I e.g. tossed out my gas-powered car and bought a Tesla, I'd have the environmental cost of manufacturing a Tesla. That would need to be lower than the environmental cost of the gas I'll use for the rest of the life of my car. I don't think it is. There are reasons to buy this stuff (e.g. to support the green industry). That doesn't excuse the propaganda and the fake numbers.

ljf 3y ago
Agree on some points here - in the UK I spend about £300 combined on gas and electricity. But your boiler sounds interesting - if it is 40 years old it will be wildly inefficient compared to boilers from the last few years - on changing our 10yo boiler we saved about £100 a month across the year - But I only expect that boiler to last 10 to 15 years - but that is OK, by then I'm sure I'll be moving to electric heating and hot water, as I can only assume gas will be phased out.
- blagie 3y ago
  I'm not quite sure how a boiler can be efficient or inefficient. It seems like for every watt of power going in, I get one watt of heat out. That's basic thermodynamics. If heat doesn't make it into the water, it still ultimately heats my house. Perhaps language issue? My boiler heats the water for my radiators which heat my house. That's not the same as my hot water tank, which heats running hot water. Here, where modern ones do tend to leak less heat into the air, and these do have a limited lifespan as the tank corrodes. Can you explain? I feel like the only way I could go up in efficiency is if I sucked in heat from the outdoors with a heat pump.
  - ljf 3y ago
    Modern gas boilers can extract far more heat from burnt gas than older boilers. https://www.britishgas.co.uk/home-services/boilers-and-heating/guides/boiler-efficiency.html https://www.britishgas.co.uk/home-services/boilers-and-heati... Older gas boilers (esp if 40yo) are likely to be less than 60 percent efficient, potentially far less. Modern ones can be over 90% efficient - this was a big saving for me on my hot water and the gas power central heating radiators. With older boiler you lose a lot through the flue/exhaust, so it never gets to heat your house.
    - blagie 3y ago
      I see. That makes sense. That actually seems like a very solvable problem with older boilers by adding something like a heat exchanger on the flue / exhaust. That should be a <$500 retrofit, and should bring efficiency up to >>90%.
      - ljf 3y ago
        Sounds like a great engineering challenge! I don't know a lot about boilers, but I do know that obstructing the flue in any way risks carbon monoxide poisoning - which may be the reason these things don't (yet?) exist.
        blagie 3y ago
        I don't think it's a challenge at all. I could build one for my house for <$1000 and <2 weeks work. I could do all the design work for one which could be manufactured at scale in <6 months and <$500 per unit (although I have no idea how much extra there would be for regulatory and similar work in this domain, and the NREs for getting a production line would be quite a bit extra too). Short story is that a heat exchanger would add resistance to airflow, but that could be trivially countered with ... a fan. I could design a control system for setting fan speed to make it look like an unobstructed passage for <$30, but more likely than not, it'd be sufficient to just have a powerful enough fan to have more airflow than an unobstructed flue. Disclaimer: I've done work in an adjacent field, and I'm confident about all of the above working. I can give you the parts list almost off-hand if you want a longer story, right down to the pressure sensor I'd use if I needed a control system. That said, I have close to zero background in civil engineering, regulatory requirements around things like this, and similar. My knowledge of thermodynamics and thermal engineering is also quite good, but my knowledge of HVAC specifically could fit on the head of a pin. I give the background so that you can decide whether or not to believe me. :)

by blagie 3y ago

ljf 3y ago

Agree on some points here - in the UK I spend about £300 combined on gas and electricity. But your boiler sounds interesting - if it is 40 years old it will be wildly inefficient compared to boilers from the last few years - on changing our 10yo boiler we saved about £100 a month across the year - But I only expect that boiler to last 10 to 15 years - but that is OK, by then I'm sure I'll be moving to electric heating and hot water, as I can only assume gas will be phased out.

blagie 3y ago
I'm not quite sure how a boiler can be efficient or inefficient. It seems like for every watt of power going in, I get one watt of heat out. That's basic thermodynamics. If heat doesn't make it into the water, it still ultimately heats my house. Perhaps language issue? My boiler heats the water for my radiators which heat my house. That's not the same as my hot water tank, which heats running hot water. Here, where modern ones do tend to leak less heat into the air, and these do have a limited lifespan as the tank corrodes. Can you explain? I feel like the only way I could go up in efficiency is if I sucked in heat from the outdoors with a heat pump.
- ljf 3y ago
  Modern gas boilers can extract far more heat from burnt gas than older boilers. https://www.britishgas.co.uk/home-services/boilers-and-heating/guides/boiler-efficiency.html https://www.britishgas.co.uk/home-services/boilers-and-heati... Older gas boilers (esp if 40yo) are likely to be less than 60 percent efficient, potentially far less. Modern ones can be over 90% efficient - this was a big saving for me on my hot water and the gas power central heating radiators. With older boiler you lose a lot through the flue/exhaust, so it never gets to heat your house.
  - blagie 3y ago
    I see. That makes sense. That actually seems like a very solvable problem with older boilers by adding something like a heat exchanger on the flue / exhaust. That should be a <$500 retrofit, and should bring efficiency up to >>90%.
    - ljf 3y ago
      Sounds like a great engineering challenge! I don't know a lot about boilers, but I do know that obstructing the flue in any way risks carbon monoxide poisoning - which may be the reason these things don't (yet?) exist.
      - blagie 3y ago
        I don't think it's a challenge at all. I could build one for my house for <$1000 and <2 weeks work. I could do all the design work for one which could be manufactured at scale in <6 months and <$500 per unit (although I have no idea how much extra there would be for regulatory and similar work in this domain, and the NREs for getting a production line would be quite a bit extra too). Short story is that a heat exchanger would add resistance to airflow, but that could be trivially countered with ... a fan. I could design a control system for setting fan speed to make it look like an unobstructed passage for <$30, but more likely than not, it'd be sufficient to just have a powerful enough fan to have more airflow than an unobstructed flue. Disclaimer: I've done work in an adjacent field, and I'm confident about all of the above working. I can give you the parts list almost off-hand if you want a longer story, right down to the pressure sensor I'd use if I needed a control system. That said, I have close to zero background in civil engineering, regulatory requirements around things like this, and similar. My knowledge of thermodynamics and thermal engineering is also quite good, but my knowledge of HVAC specifically could fit on the head of a pin. I give the background so that you can decide whether or not to believe me. :)