Advice for hydronic heat only boiler

[Smoky]

We live in an A-frame home, 1300 square feet, in northern Wisconsin. The basement has a sand point well that has a 20lb well pressure tank. We have a 96k Burnham propane boiler used for hydronic heat that is about 20 years old and a conventional gas water heater for domestic. We noticed our gas bills increasing over this past winter. Our gas company told us we were using 15 gallons of propane per day. We called two companies to take a look. One showed me a picture on his phone and explained the heat exchanger looked bad and questioned our water quality, told us it could fail at any time. Another company said our spirotherm air eliminator wasn't doing its job and needed replacement. Regardless, I decided it was time to upgrade. I had planned on a high efficiency combi boiler but I'm certain our water pressure could not keep up over time. For example, if my wife is watering the garden I can't flush the toilet. We can take endless hot showers though and overall the low water pressure isn't an issue for us. So now, I'm thinking about a new boiler just for the hydronic heating and keeping our old water heater for domestic. I was thinking perhaps a Rinnai - 112K BTU - 95.0% AFUE - Hot Water Gas Boiler might work in our situation. Would appreciate any advice or boiler recommendations for us.

 

[Fitter30]

Any condensing boiler is 95% efficient when return water is below 130° above 86%. Don't oversize the boiler they run more efficient running than cycling

 

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[Jadnashua]

A-frames aren't notorious for good insulation and efficiency. But, there are ways to figure out what size boiler you really need. The likelihood is you could be perfectly comfortable with a considerably smaller one.

Basically, you can look up the energy content in a gallon of propane, then using the efficiency of the existing boiler and looking up the heating degree day information for your area, and see what the actual load is. It's best to not have a boiler more than 140% of that number to account for a cold extreme and have the ability to recover from a setback. Anything more is a waste.

If you get an indirect water heater tank and set it to be a priority zone, it will direct all of the heat to that tank when it calls for heat. Unless you're running something like a spa with continuous hot water use throughout the day, you typically don't notice that, and because a typical boiler will have a bigger burner than what you'd have in your tank, it will reheat the water in the tank faster so often, you can get by with a smaller tank. Some of those are available with a stainless steel tank and guaranteed for life.