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Optimized_Orangutan t1_j7utuz9 wrote

Reply to comment by SomeConstructionGuy in Seeking Advice: Boiler by Some_Mediocre_Guy

This. Also they aren't going to handle any significant square footages even with in floor radiant. They just don't have the recovery rate needed to get the job done over 1000 square feet of 1/2" tube during cold weather. You can add a big buffer tank but at that point you've lost the benefits of the heat pump and could get the same/better efficiency from a modern propane or natural gas condensing tankless water heater for a third of the cost. Heating water with electricity for space heating in Vermont is generally not an optimal solution. Our rates are too high and our winters are too cold.

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SomeConstructionGuy t1_j7uv6sg wrote

The key is to avoid needing recovery by having a finely tuned reset curve and very balanced loop flows. We built 1500sf of shop/garage and 1000sf of living space heated with a spacepak. Propane only kicks on below -5 or for domestic water heating. Average calls for heating are in the 6-8hr range, it’s basically on and heating all winter. Not cheap or easy and likely not worth it…

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Optimized_Orangutan t1_j7uw4bi wrote

Definitely not worth it. Could have heated that whole space and done your domestic water with a single tankless propane unit that would run less than 4 hours a day. If you're paying more than about 9 cents a kilowatt hour for power, LP or NG will be a more cost-effective method anyway still. Let alone being a fraction of the upfront cost... But people insist on paying more to pay more cause "propane bad".

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SomeConstructionGuy t1_j7uxb6t wrote

I agree the roi is long, but dollar per btu the spacepak is cheaper than propane and oil even at $.185/kWh down to about 0 in this setup. Aiming for short run times is directly contradictory to achieving high efficiency with a condensing boiler and high mass setup.

And it wasn’t my house, we just built it. But you couldn’t convince me to use a combi if it was free. I’ll always want an indirect with recirc

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Optimized_Orangutan t1_j7uxrjh wrote

Absolutely, combis are the suckers bet. Indirect has some built in inefficiencies too because of losses across exchangers. An open system on the other hand, when done correctly, is superior to both. Most people don't know how to do an open system correctly though/are unjustifiably scared of it.

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SomeConstructionGuy t1_j7uyoo1 wrote

Yeah it seems open system have been in the realm of diy for a long time in our area. The problems aren’t a result of open systems themselves but of unqualified design and install. That’s given them a bad rap.

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