Propane Boiler and Water Heater Thoughts

In looking at the tag on my boiler, I am confused (I am easily confused )



So, there seem to be 3 numbers for BTU and I am unsure which is the correct one to look at; Max BTU input per hour (97,500), DOE Htg. capacity BTU/hr (80000) and Ratings BTU / Hr water (70,000). I believe I should be using the 80,000 BTU/hr as a baseline (without factoring in DHW). Is that correct?

 

Let me start this with a disclaimer..... Everything I know about heating has come from bazooka joe wrappers and this site... I.E., I have no formal school training.. That said, from some quick research, it looks like the 80,000 number is if the heating appliance is installed in the conditioned space.. The 70,000 number accounts for heat loss and is the minimum guaranteed heat if the appliance is installed outside of the living space... So, I would think that the output is somewhere in the middle. That boiler could very well keep up with your DHW heating requirement but you have no way of knowing since you have a separate burner on your DHW. If you had an extra zone plumbed to a DHW tank the boiler might just fire more often to keep up with the DHW demand. One experiment you could do is to pick the coldest, windiest night in January, shut off the pellet stove and set up an hour meter to see what percentage of time your boiler is running to keep your house at a given temperature.. This might be more in depth than you want to research but it would be a good experiment. If the boiler is only running 25% of the time, then your insulation might be better than expected or boiler could be a bit oversized. If it's running 80-90% of the time, you have significant heat losses and the boiler might be undersized.. Again, a disclaimer that I have no formal training in this..

 

I see. So the boiler is outside the conditioned space, so I would expect 70,000 and the other 10,000 is lost to the basement and perhaps up the chimney. If I were to lose my mind and place the boiler on the main floor, the BTU rating would go to 80,000 since any escaping heat would still go into the main floor.

I just have to keep in mind that I have removed almost all exterior walls and plugged up the air gaps, installed better insulation and a vapor/wind barrier (which was not present at all) before putting in the new sheetrock. I've also installed new, more efficient windows, so theoretically, the BTU needs would be lower - although with the acoustical tile ceilings instead of sheet rock there is still a lot of heat loss up to the attic.

Thanks for clearing that up.

 

You're welcome. Just think of the 70000 as the minimum guarantee. That number could be 70, 71, 75 or even 78... "Waste heat" that goes to your basement isn't really waste heat if it's keeping your pipes from freezing.... I believe that chimney losses (exhaust gas up the chimney) are considered losses due to combustion efficiency while the boiler is firing. Losses up the chimney while the boiler is off would go into the other category.

 

Sure wish I knew about boilers so I could offer advice/help.

It appears by the info on the tag that your boiler burns 97,500 btu of fuel. Out of that 97.5K, you feel 80,000 btu of heat around your home. The rest of the 17500 btu goes up the chimney (metal pipe to masonry?) This would be referred to as 80% efficient since you are only using around 80KBTU of the 97.5KBTU that you are burning.

The rating of 70,000 is allowing for the heat loss that will occur when the boiler circulates the water throughout the system. So now you're down to about 70% efficiency or of the 100% of the fuel you are burning, you feel about 70% of it.

True, that other 10% of loss would be given up inside of the house, right? Its just not directed and felt wherever it is desired.


I found this and hope it helps to explain a bit more for you.
Boiler Ratings Explained

 

This is interesting.. Dead Men's Steam School by Dan Holohan | Dan Holohan | Heating Help Talk about heat loss 14 minutes in... Didn't pay for the extended video.

 

Burnham was the most installed boiler that we used when my dad had his boiler business. They make a great unit.

 

Your logic jives with everything that I know. I went to seminars and trade shows, buy my schooling wasn't anything to do with boilers.

 

Yes, that's right about combustion losses.

Given no other hearing demand( she, another zone, etc) you can and should start with the btu rating you had before. You can oversize, as precaution, but you don't need to unless you are expecting to add another "zone". Better insulation than you previously had will just allow the boiler to run less.

 

Yeah, the heat that escapes from the unit itself, while technically "waste" apparently was enough to keep the basement warm enough to prevent freezing (either that, or they ran electric space heaters). They do have a small loop of extra piping that goes along the ceiling in the area of the outdoor faucet line, so they wanted to make sure that stayed warm.

That link was a great read, and you did a good synopsis - thank you!

I feel that you guys have given me enough of an understanding that I can at least talk semi-intelligently with contractors, and hopefully detect BS when they start spouting it (OMG - you should have heard all the stuff different mfg reps were saying when I was getting windows quoted - and there I had a clue).

 

Try using Angie's list or Home Advisor... Had luck with both..

 

I'm going thru more of the info on that site - a lot of good info including a checklist of stuff that I should require and/or ask about.