Replacing old gas boiler

GreaseMonkey

Hi,

We need to replace our 1980's Vaillant gas boiler. We have hot water baseboard heat with a mix of fin tube and cast iron. When the boiler was working the water temp was set at 180 degrees and we had no complaints. The boiler is located in a closet in a room that would be nice to be able to use as a bedroom. Hot water tank is in the same closet, gas fired 50 gallon tank that is 8 years old. What is the longest lasting, least maintenance required and quietest boiler that is the safest in a bedroom? We could provide sealing doors on the closet or any other safety measure. Draft venting, direct venting, cast iron, mod-con are all options. There is no drain in the closet or nearby for condensate. A pump would be required for condensate as this is located in a half basement. House is 2,400 square feet, well built 1960's home with new windows. Welcome any comments or suggestions.

Thank you.

Hot_water_fan

What is the longest lasting, least maintenance required and quietest boiler that is the safest in a bedroom? 

Unfortunately, there is no answer to this. They’re all safe indoors, but otherwise a lot comes down to installation and frankly, luck.

jesmed1

Especially because you're space limited, you want a properly-sized boiler, meaning not one that's oversized because someone didn't do a heat load calculation for the house and instead used a rule-of-thumb with a safety factor that ends up oversizing the boiler. The way to correctly size the new boiler is to do a heat load calculation on the house. There are several methods, but the most accurate uses the number of BTU's you actually burned in heating the house in a recent heating season. So if you can corral all your gas bills from the previous year and add up the total therms (1 therm = 100,000 BTU), you or a heating pro can do a heat load calculation that should be very accurate.

The result will be the number of BTU's your new boiler needs to output at the design temperature, ie the 99th-percentile lowest outdoor temperature in your region. Maybe your existing boiler was properly sized, but if it was oversized, now's your opportunity to correct that mistake.

Depending on where you live, your heat load could be under 20 BTU/sq ft, since you say the house is well built with new windows. So you could need as little as 50MBTU/hr, or less. But again, someone should do the calculation. If you want to run the numbers yourself, here's how:

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

GreaseMonkey

I looked over the last 2 gas bills. 1,195 terms last year and 1,217 therms this year. What's the next step?

Hot_water_fan

@GreaseMonkey that link is all you need. Find the Heating degree days and you’ll be on your way

GreaseMonkey

I see the link now, thank you. That will size the boiler. Any recommendations on type of boiler? Cast iron, mod-con, combi, brand, model?

Hot_water_fan

It’s not really a brand thing: get one that’s well known by a reputable installer who has parts stocked. Mod con vs cast iron are both fine, a competent installer will make either work, a hack will screw up anything. 

jesmed1

"What is the longest lasting, least maintenance required..."

I'm not a pro, just a semi-informed homeowner. High-efficiency condensing gas boilers are probably not going to be either the longest-lasting or least maintenance, so I would be leery of those. You'll get maybe 10% better efficiency, but in my book, that's not worth the extra up-front cost, the shorter life spans (15-20 yrs maybe) and potential higher costs if/when some expensive circuit board or other component fails. I'd rather have an 86% efficient cast iron boiler that I know is going to be more or less bullet-proof for 25+ years and is dirt simple to fix. YMMV. Also, a cast iron boiler will be easier to install with fewer opportunities to screw it up.

The noise factor may be the wild card. You can probably find a super-quiet high-efficiency boiler, but then you have to decide if it's worth sacrificing your other two priorites.

EBEBRATT-Ed

Not sure about a boiler in a bedroom or even in a closet in a bedroom.