Looks like we’re not the only ones concerned about water heaters.
Rindert
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My water heater’s exhaust regularly measures 420F. I installed a grill thermometer in the flu pipe. It just keeps me motivated to keep working on this.
Rindert
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Rindert, 420 F is more then 200 C! Way to much for a gas powered heater. Biden is right! If those numbers are common in the US, government should take action. The further under 100 C the better. I tried to keep it at 60 C, a lot of condens anf efficiency above 100 %.
My woodgas boiler needs 420 F to function ok and that hurts to leave it to the birds.
And if you are investing in a new boiler , go for instantanious condensing type.
Edit, you need low temp process water of course to get the boiler condensing. Sanitair water under 140 F and floor and/or wall heating 85 F.
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Part of that is they need heat to make it up the exhaust pipe so CO gets pulled out, but that seems too hot.
They also make the signature 900 series now which is supposed to be 30% more efficient. It is called the condensing type. I don’t think it eliminates the exhaust flu like the furnaces do though.
You can switch to the tankless system as well.
If you want to switch to electric you can get the heat exchanger type which might be cheaper to operate then propane if that is what you have. The real bonus to that is you don’t have the exhaust vent that sucks heat out of your house.
There are tax rebates for the super high efficiency ones, but I don’t know if they make up the cost difference with your usage pattern at this point.
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I recently replaced an old gas waterheater and gas dryer. I purchased a electric heat pump to replace both. As a single person i am saving about $100 a month. I am pretty sure the old water heater was horrible on gas consumption. That unit was probably 40 years old had the burner replaced 2 times iirc.
The dryer take something on the order of 1.6kw to dry a load but it is slow a little over 2 hours.
I don’t remember the actual power consumption of the water heater. They where definitely more expensive to buy but i am happy with my lower monthy bills.
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I looked at water heaters at Home Depot not long ago. You can still buy one, like what I have, for $600.
The problem with the high efficiency ones is they are expensive and require a lot of expensive maintenance. Contractors will tell you to go with the old ‘B-Vent’ type.
I don’t think it needs to be that way. I think anyone with reasonable welding skills can make something better.
Rindert
This is a full scale layout. I have not yet built one. Ask me any questions.
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I am not saying you can’t design a better one, but I would look at the condensing ones design, and what the requirements are for what the air temperature needs to be to prevent downdraft. I would also look at the heat exchanger for the 95% efficient furnaces simply because they also were stuck at 80% efficiency, before they did all the condensing, and they don’t require a chimney. There is air exchange.
The high efficiency electric ones are air-air heat pumps, which might be easier to add a solar thermal panel for the air inlet pipe so incoming air hot before entering the loop which would save compressor time. or if you have a heat pump, you can preheat the incoming water in another tank prior to entering the water heater.
The super high efficiency have/had rebates for like 1k.
Then with water heaters, they require a coating to protect the metal from rusting out. which is part of what a sacrificial anode rod does.
Then the last concern, I can think of is controls to make sure the water doesn’t get too hot. Otherwise it can scald and cause severe burns.
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What is the plan? Heatexchanger?
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Best thing there is a mixing valve on the output i did this on my hot water tank i had with the Tarm wood boil in my last house. It was mechanical you set the temperature and it would mix cold water to your hot to get the correct temperature. That worked great i had a hot water tank about 700 gallons that was R60 insulation outside the house and the boiler would heat it to 190F. There was a copper coil for the hot water that would supply endless hot water at whatever i set it probably about 140F. That system would provide hot water for about half the summer just from the last heating of the house in the spring. If i was to do it again i would have a small electric heating option from a single solar panel for the summer. Or a larger solar system for electric as an opportunity load. The tarm wood boiler did suck to start in the summer sometimes i would heat the tank back up with the oil furnace middle of the summer.
You also do need a pressure release for steam on any hot water system or you make a bomb.
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Based on my experience with rocket stoves I predict that this one will condense some water out of the exhaust.
I have been thinking about that. I may have to airtight seal the flu so it doesn’t work in reverse during hot weather. It might end up being easiest to use a 3 inch PVC flu. I’m going to have to do a lot of testing.
See post 56. Essentially I will put the barrel (heat exchanger) and heat riser from a rocket mass heater in the bottom of a tank.
Yes, I haven’t forgotten.
Rindert
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I made a full scale layout that I plan to use for fabrication. Scale is in inches. Ask me any questions.
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Any trick to darkening up the lines on my end? I can barely make out lines.
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I didn’t think it was a trick, but if you just click on the drawing it sort of opens up. Then if you click on it again it zooms in. Then you can scroll up and down. And if you want to scroll left and right just hold down the shift key and use the mouse wheel. That should allow you to see everything. The odd structure in the middle is my attempt to show the heat riser with a spiral baffle around it. The wavy lines represent insulation. Thanks for your interest.
Rindert
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If you click on the image, like Rindert said, there is an option to download the file. I did that and put it in an editor (Like Microsoft “Paint”). It is then easier for me to see the contrast in the lines. I pasted the image into the Windows 11 “fancy AI” editor and did an “Image enhance”, that was not as good as just looking at the downloaded original, zoomed in to the area of intrest. 
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I tried to enhance it in GIMP. Not very good.
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