Please guesstimate how much coal I'll use.

It seems that HVAC contractors don't know much about sizing heating appliances to meet the need. I'm experiencing it right now. The first two contractors I've sought out to give me a NG boiler estimate want to make it gigantic. For some reason they keep telling me that their goal is to make me happy. Waiting on the estimate from a third at present.

I told one of them that for 10 years I happily heated our house on exclusively a 13.5 KW resistance boiler, with only 46,062 BTUH input/output. He insists however that I need a 100,000 BTUH boiler (despite that we have had blown in foam insulation installed in the walls since the resistance boiler days). The other guy (whom I also told about heating for 10 years with only a 13.5 KW resistance boiler) came in with a slightly smaller 80K BTUH ultra-high efficiency condensing boiler, but thought I was totally off base in my request to have a 30 gallon buffer tank installed to eliminate boiler short cycling for what is a low volume boiler with only a 1 gallon water tank. He refused to consider the buffer tank and then quoted a system without this feature against my instructions, but I'm certain that it was to make me happy.

This is why I'm highly skeptical about their ability to accurately perform a Manual J heat loss assessment.

Maybe they are nervous about downsizing too much from the 130k input boiler you have chosen to use? Maybe you have enough installed radiation that they are trying to make sure the boiler can actually carry the attached load? Maybe they want to make sure you can run a low-volume showerhead in real time? Just spitballin' here.

Mike

Pacowy wrote: ↑

Thu. Sep. 12, 2019 1:04 pm

Maybe they are nervous about downsizing too much from the 130k input boiler you have chosen to use? Maybe you have enough installed radiation that they are trying to make sure the boiler can actually carry the attached load? Maybe they want to make sure you can run a low-volume showerhead in real time? Just spitballin' here.

Mike

All of that may be part of it. My combined HWB radiators (garage included) can deliver roughly 75,000 BTUH if supplied with 180 degree water at 20 degrees Delta-T (returning at 160 degrees). But they should also just barely heat the house on the coldest day of the winter for the case of 150 degree supply and 130 degree return. 150/130 is about what the resistance boiler was capable of when running full out and continuous, and with all 4 T-Stats calling. Normally it ran at 160/140 when there was less than non-stop full guns demand from all 4 T-Stats. Admittedly the resistance boiler was a bit undersized at 46K BTUH of gross output, but only on one or two days per year. I'd like to have a boiler capable of 56K gross/49K net BTUH output installed. But I can't get buy-in from the HVAC contractors for a boiler that small.

lsayre wrote: ↑

Thu. Sep. 12, 2019 1:25 pm

All of that may be part of it. My combined HWB radiators (garage included) can deliver roughly 75,000 BTUH if supplied with 180 degree water at 20 degrees Delta-T (returning at 160 degrees). But they should also just barely heat the house for the case of 150 degree supply and 130 degree return. 150/130 is about what the resistance boiler was capable of when running full out and continuous, and with all 4 T-Stats calling. Normally it ran at 160/140 when there was less than non-stop full guns demand from all 4 T-Stats. Admittedly the resistance boiler was a bit undersized at 46K BTUH of gross output, but only on one or two days per year. I'd like to have a boiler capable of 56K gross/49K net BTUH output installed. But I can't get buy-in from the HVAC contractors for a boiler that small.

Are not most of the NG /Propane condensing boilers capable of a huge delta output of BTU? say like 8-85mbtu? upt to like 220mbtu

Few if any of them have turn-down ratios that good. Most are at about a 4 to 6 to 1 turn down ratio. But for any model line, generally the greater their top rated output, the better their turn down ratio.

Short Cycling is the number one reason for modern boiler failure. The more often it short cycles, the more and the quicker it soots up, and the quicker it fails. I've ran the numbers, and if ones radiators are designed as mine are (for old high water capacity boilers) all of the condensing boilers short cycle severely if they do not have a buffer tank in the primary loop. Many will short cycle even with a buffer tank, and particularly if it isn't large enough. Any boiler that fires less than 10 minutes before cutting off is considered to be short cycling. With a 30 gallon buffer tank the two boilers I'm looking at (factoring in turn-down and all) I still have scenarios where they will only cycle for a bit more than 7 minutes before cutting off at high limit. Take away the buffer tank and they have certain scenarios where they may only run for 1 minute or perhaps less and then cut off (over and over and over again). The higher the boilers output, the more it short cycles. The bigger the boiler, the higher its minimum (turn-down) output, even though the bigger ones generally have slightly better turn down ratios. So the bottom line is: The bigger the boiler the more it short cycles, as well as the more severely it short cycles.

I had one HVAC guy tell me my zones are too short for these low capacity boilers. He recommended to me that rather than add a buffer tank I should combine (and thereby reduce the number of) my zones so the boiler doesn't short cycle as much on a T-Stat call for any given zone. Combining zones adds more water and more heat output to each loop. With all four of mine combined I have about 16 gallons in the system, which is still less than 30 gallons. Amazing!!!! But with the added bonus of the extra heat output of a single big zone he is right, the numbers crunch to show no scenario with a need for the buffer tank..... He told me to eliminate heat in my garage and combine my other three zones into one long zone. He never considered the devastation this would have on my Delta-T. Or that I'm not fond of a cold garage, particularly when the bedrooms sit on top of it. But he was helping me be happy.

It’s funny I found this thread I was just thinking the other day if I keep track of how much coal I use per use that would give me an idea of how the coal stoker is doing. Kinda how you keep track of the gas mileage on your car when you fill up. Then I was thinking it may be hard to keep track as if it’s really cold I may go through more then if it’s above freezing. From December last year to April/ May we used 5 ton . This year we may use wood also. I’m still trying to find the right combination. Just wondering about how much other people use to heat a 3 story house and do any of you guys use coal to heat hot water also. If so do you turn down the water pressure in the house to allow a little hot water. The wife likes the hot water at 170°