Back up boiler size

Surf20 · February 2014

My wife and I have a 1700 SF house in Maine. Open concept with vaulted ceilings. Insulation is good except for the fact that the walls are only 2x4 construction. Also, house is pretty well sealed (vented properly too). We use a wood stove as a primary heat source and have a system in place to circulate air that gets trapped at the ceilings to the colder parts of the house. We are a three person family and the house is 2.5 baths. We only need the boiler as a back up really.. for the nighttime, when we go out for the day or are on vacation.. basically anytime the wood stove goes out. We don't move the thermostat up past 55 during the winter as the wood stove does the trick. My question is... we need to replace the current oil fired boiler and have no idea what to get. Any recommendations for our situation would be greatly appreciated. We are open to different options for heating our domestic water as well...i.e. tankless. Thanks everyone!

Aaron_in_Maine · February 2014

Heat loss

First you need to get a heat loss done on your house. This will tell you the size of the boiler you need. Most likely if you stay oil the smallest one you can get will work. Hot water could be done off the boiler with a indirect water heater or you could go with a on demand gas water heater.

STEVEusaPA · February 2014

X2 for what Aaron said.

No matter what you go with, properly size it to do everything you need without the wood stove. It wont cost you more money. And you never know what could happen to the 'stove stoker' in the future, and you'll be glad you have some automatic heat.

SWEI · February 2014

Fuel options

Do you have natural gas available?

What are your electric and LPG prices like?

Assuming you have sufficient panel capacity, an electric resistance boiler will probably have the lowest first cost and should be almost maintenance-free. If it's only a backup, operational cost will not factor in much.

If there's no natural gas, you might consider a small solar system for DHW, paired with an electric tankless. Solar preheat will dramatically improve the performance in winter, and you'll probably run all summer without using $5 worth of electricity.

Jamie Hall · February 2014

Having lived with various options...

Personally, I'd stick with a small oil boiler, as Aaron suggested. The alternative would be LPG, which has some points very much in favour, but at least last I looked was a toss-up on cost. If you do go LPG, make darn sure the gas tank and pipes are sized for the maximum demand on the coldest day. That sometimes gets overlooked, particularly if you are in an area where there are a lot of "second homes".

Either oil or LPG can be run without a problem with a generator, if it is properly installed.

Electric can't. If the power goes out, you would have to stoke that stove, or freeze.

Steve has a good comment too: size the boiler big enough to actually heat the house comfortably. There may be a bit more first cost -- but it won't cost any more to run, and if it should happen, and God forbid it should, the stove stoker person isn't able to stoke and you want to stay put, you'll be much happier. Been there, done that.

Big Ed_4 · March 2014

Small Efficient Boilers

When you find out what is needed through your heat loss calculation . You will find out the better smaller oil fire boilers come from Europe ... Like the Buderus G115 ... Well made , three pass, positive pressure boilers and there indirects are well made too ... Throw the outdoor reset on with the remote room sensor ... When the fire cools down the boiler would take over ...

Back up boiler size

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