I have a converted boiler, that I believe used to be coal because there is a coal shoot in my basement. But anyway, its been converted to natural gas, and I was browsing the Weil Mclain products. It says on the burner that my boiler is minimum 75000 BTU, maximum 150,000 BTU. The smallest weil mclain is 80,000 BTU. Obviously this doesn't match up, but here's the deal. I don't know if I need something as large as what I've got? My house is only about 750 square feet, full basement (but no heat in the basement right now). Its old, 1921, so the insulation value probably isn't all that great.

But how much does the efficiency matter? Is 80k BTU on a high efficiency boiler as good as my relic? Or does that matter? And would 80k BTU be enough for a small house like mine? Thanks guys.

It sounds like the 80k BTU boiler will be large enough for your house, but a lot of the new heating and air equipment have two stage models. This way if the first stage does not satisfy the load the second stage will kick in. Remember to check the flow rate for a water boiler and the steam generation rate for a steam boiler. If you have a water boiler you would be wise to replace it to match the new one. AO Smith has several boiler to compare to.

Thanks for the info. I have a hot water boiler. How do you check the flow rate? Thanks again.

80,000 thousand BTU is way to large for a 750 sq ft house. The boiler will short cycle all the time wasting energy.

I suggest you do a real calculation to see exactly what you need. With utilities going up all the time you will probably want to save all the $$ that you can.

With a loose house a 50,000 BTU boiler will run away with it.

Example This house is 2,600 sq ft. The boiler can fire at 40 or 80 thousand BTU. When the temp gets down to below zero I have to kick it up to the 80,000 high fire rate other wise the 40,000 fire rate does just fine.

There are some high efficiency models that have a turn down of 5. So it is rated for 50,000 BTU but will turn down to 10,000 BTU when more heat is not needed.

The old way of calculating boiler size went out the window back in 1973 during the first energy crunch.

BTW flow rate can be determined by the velocity of the pump allowing for the pipe size in the configuration. Check B&G web site ( Bell and Gosset)

Pump manufacturers, industrial pumps, residential pumps, compression tanks, valves, air removal devices, commercial tanks, residential tanks, heat exchangers, reducing valves, expansion tanks

Only put in exactly what you need to get the job done.

It's the smallest they make. And since my current boiler is 75k-150k BTU. What if I used it to heat the basement, which is also 750 square feet? So total heat would be 1500-ish? But the basement will be much better insulated than the main floor.

Actually boiler selection should be done using a plan of the building with all the windows and doors listed. Room sizes and insulation valuse for walls and attic space.

Anything else is a guessing game.

((Its the smallest they make))
Who cares. There are other manufactures out there that have given up on cast iron boilers. There are also companys out there that do have smaller boilers. Do your homework first then get the boiler that is correct size for the home.

The only reason I'm looking at Weil McLain is because my father in law sells them, and will install it for me for free. And I can get the boiler at cost, which is impossible with other brands. And the savings I'll get will be huge comparibly, not to mention make my father in law happy, and that's worth something. So its either I replace it with this brand, or keep my ancient monster. I and he will check the house to make sure we get the right boiler, but I just wanted to do some research first, and understand what I'm looking at. I never do something blind.

((but I just wanted to do some research first, and understand what I'm looking at. I never do something blind.))

What a waste of time. You can only buy one brand. On top of that your father in law can get you the unit at cost. This is great but the real kicker is that you do not trust your father in law because you were afraid to ask him these questions. What a shame.

No that's not it at all. What's with the assumptions? Do you know me or my father in law? I like to research things like this because I'm interested. I like the advice I've received on this site and everyone has been really helpful. Sometimes when I have a quick question it might be easier for me because I work with computers to just ask some other advice, rather than phone my father in law, when I suddenly think of a question. I might ask him a question on the phone and didn't think of something. I just wanted some opinions, but I gues you are right I'm just wasting my time.

I call them the way I see them. If you do not trust someone who has years of experience like your father in law especially since he is really familiar with the type of boiler you want that is a shame.

My father in law has passed but when I had questions within his field of study he was the first and only person I asked questions of. I trusted him because he was real good at what he did. No one on this board can give you a better answer than your father in law as long as he really knows what he is doing. Stop trying to out guess the old man he is much smarter than you are in his field.

I'm just doing some research online, and I spent all day talking with my father in law yesterday (Christmas) and I trust him 100% and always ask him questions. But its late here, and I don't need to bother him right now. I can call tomorrow, but I was just curious. Sometimes I start surfing and see something and have a question. Its midnight, and I don't think I should wake him. The question I asked is based on the fact that neither of us yesterday new the btu's of my current boiler, and I just wanted a comparison.

I don't know why you think I don't trust him, or where you got that opinion from.

I thought we were here to help others by giving some of our insight.. not insult them. How does someone get to have some much knowledge and still be so disrespectful. Kingsx I am sorry that you have had to put up with such a judgemental EXPERT. If you need more help please continue to ask because some of us are here to help others, not insult them.

((How does someone get to have some much knowledge and still be so disrespectful))

Actually it is not disrespectful. What we have here is a person who has a professional as a relative and for whatever reason still feels compelled to ask questions.

Anyone who has been this and other business for a good amount of time catches the usual drift of these conversations.

There are 100 correct ways to do things in the HVAC biz and everyone has there own way of doing things. It is extremely difficult to give advice when it could cause a conflict among family members especially in laws.

With that said the person asking the questions should stick with the in law because he is probably going to do the work and does not need to be told by his son in law that get just enough info on this web site to be dangerous and now he wants to tell his father in law how to do the job because some one here said to do it that way.

I have been around toooooooo many years to play into that game.

I was not trying to insult him because if that was my intention I would have done a much better job. I was trying to save both him and his father in law from a could be nasty situation that would involve both and could have long term ramifications.