Replacing an under-fired boiler

Diar

Thanks! I live in a cold area ( Boston ) and have to buy a small commercial unit ( a Weil McLain 480 ). Would it make any sense to install a lo-hi-lo burner on a Weil McLain 480 ( ~1250 sq ft of steam )? The 480 doesn't ship with a burner that can support lo-hi-lo, so Weil McLain suggested that I look into Reillo, Power-Flame, etc.

Any guidance would be appreciated.

Thanks,
Diar

Diar

Replacing large under-sized steam boiler

Hi All,

Since my family bought our 5000 sq ft old house, I have been underfiring a Weil Mclain 778 ( rated for 2500 sq ft steam ) at 3 gallons/hour of oil, which only generates 1058 sq ft of steam for my system that has 1100 sq ft of a connected load ( not including piping pickup factor ). While I have been paying high oil bills, the system typically only has to come on for only 10-15 minutes before the house is toasty warm, so I'm pretty satisfied with my heat currently.

Now that I have to replace my old boiler, if I size the new boiler according to the connected load + pickup factor=1450 sq ft, then I must now fire the boiler at ~4 gallons/hour.

My problem is that even though I realize that the this is properly sized, I am worried that firing this new boiler at 4 gallons/hour will only lead to me having an overheated house and paying more money to heat it. Is this a valid concern? If so, then what can I do to help prevent spending more money:
- Buy a boiler that produces less than 1450 sq ft, since my old boiler running at 1058 sq ft seemed to heat the house fine.
- Underfire the new boiler, even though I'm not supposed to?

Any advice would be greatly appreciated.

Thanks,
Diar

clammy

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Not to sound insulting but if it where under fired or sized the house would not heat up so fast nor would it cycle be so short.i would first figure out the edr of all your raditors and convert that to btu's then either do a heat lose for your home or have some one do it for you ,maybe contact a real steam pro not the oil burner guy or a plumber check this site and get some one who knows what there looking at have them do a good look see and see what your systems story is ,as i used to do alot of service in a posh area of older homes built in the 10 and 20 i can tell you this big house big bills that's just what comes with big homes i have a small home and i pay small bills at 5000 sq.ft and burner 3 gallons a hours my quick math comes to about 80 to 85 btu's per ft it just don't seem right to me peace and good luck clammy

Diar

I have to admit that I did a heat loss calculation of several of my rooms and the radiator size was pretty close to the required amount. I agree with you, if you run the numbers on my system, it just doesn't seem to work out. Maybe it was being fired higher than I was told by my oil man. I'll be sure to check the nozzle.

The other possibility is that even though me and my wife thought the house heated fine, it might not have been heating as fast as I assumed. It may have been more like 20-25 minutes max. Would this mean that I would have saved money if I fired the 778 boiler at the recommended 6.5 gallons per hour?

The reason that I thought it might be ok to underfire a steam boiler is that I've seem lo-hi-lo burners recommended for cost savings. Can you only underfire in the spring/fall? Can you never underfire with a steam system without wasting money?

With respect to your 85 sq ft calculation, I haven't seen it before, so it is very useful. What would you expect for the btus to heat a sq ft?

Thanks for your help,
Diar

Steamhead (in transit)

Diar, you'll get better efficiency

with a properly sized boiler fired at or near its recommended rate. Also, take a look at the air venting in that system. It's large enough that some main vent upgrades might help a lot. Is it a one-pipe or two-pipe system- that is, do the radiators have two pipes connected to them, or just one?

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Ron Schroeder

Diar

Be dareful here, on Steam you need to size to the connected load its about getting the heat to the furthest radiator before it condences. Yes you might have a 3.00 GPH nozzle and nozzles are rated at 100 PSI, if someone has increased pump pressure for one reason or another then you are getting more than 3.00 GPH out of that nozzle.

Good Luck
Bruce

Diar

The main vents do need to be upgraded and its one pipe steam.

I'm starting to be convinced that I should increase my firing rate to 4 gph, so that it matches my connected load.

Thanks,
Diar

mel rowe

Diar, not to add any confusion to your decision making, but I thought you might be interested in my own experience. I, too, have an old house, with about 4000 sq. ft. The original boiler was replaced with a gas fired Utica, with 299,000 btu capacity. According to my calculations, the EDR of my radiators would be approx. 980 sq. ft.. When I did the math, it seemed at first that my gas fired Utica was undersized by about 35% or so. But then I realized that my boiler was only running about 30 % of the time, even on the coldest days in my area. Didn't seem to make sense, until I thought of all the improvements I had made to the house, such as thermal windows, foam insulation in the walls, and 8 in. of icynene foam in the attic. So the bottom line I guess, is that the old radiator/boiler formulas seem to be based on the worst possible conditions, that many times don't relate to current house conditions. In my case, if I were replacing my current boiler, someone would have a hard time convincing me that I shouldn't go down in capacity, rather than up. I have a friend also with a steam boiler and conditions similar to mine, that we ran the numbers on and found that his boiler calculated to be about 50% undersized, and yet he has adequate heat for his house.

Unknown

Diar

How did you find the correct load for your home ? Because if I'm not mistaken , the pickup factor is built into the ratings you'll find for the rads . If I'm not totally losing it already , you want to match up a new boiler to your connected load of 1100 sq. ft. The steam boiler models we use run around the 3 GPH mark with that size load . But to be totally sure , I'd remeasure every rad you got and be absolutely certain you get the right size boiler . Are you using Weil Mclain again ?

Diar

Thanks! You are right, I shouldn't have been adding any pickup factor when using the net ratings on the boiler. In addition, I am thinking of installing a Weil Mclain boiler, probably a 480. If I downfire it 10%, then it will use up 3 GPH and give me the steam I need.

Thanks again,
Diar

Diar

Maybe you were using a pickup factor of 1.33 on the measured radition load as I was. The pickup factor is already "factored" into the net sq. ft. steam rating of your boiler. Therefore, I'd guess you probably have about the right sized boiler.

Thanks,
Diar

mel rowe

I used the calculated EDR for my rads (980 sq. ft.) and the net sq. ft. output of my boiler (760). That's why I said it appeared that the boiler was undersized, and yet on our coldest days it operates only about 30 % of the time. I found on a friend's boiler system that he had a similar result. My only conclusion from this was that with our new and improved house insulation, our radiators are larger than would be currently required and installed. I think that if the rads were the actual size needed currently, the EDR would show the boiler to be significantly oversized. This also explains why my friend has no heating concerns with a EDR calculated at 620 ft. sq. and a boiler with an output rating of 317 sq ft. of steam. With an old house and old radiators, I think the improved insulation needs to be taken into account to avoid oversizing the boiler. For whatever that is worth.

Steamhead (in transit)

When a lo-hi-lo burner is used on steam

it starts on high fire and continues until the system's thermal mass has been overcome and the pressure starts to build. Then a suitable pressure control (Vaporstat in most cases) switches the burner to low fire and it just simmers along until the pressure drops again or the call for heat ends.

This mimics the old coal fire and reduces standby losses.

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Diar

Yep. I need to do an accurate heat loss on the house to determine if the radiators are too big. If they are, then I'm going to try to rotate some large radiators and move the leftovers out of the house.

I thought that I had read that thermostatically controlled radiator vents are a good way to reduce load. However, I haven't seen a way to calculate the reduction is sq ft steam based on the use of thermostatically controlled radiator vents. Therefore, I guess to use them, you'd get a slightly undersized boiler and then start reducing the temp in rooms until the system heated quickly and evenly. I'm not sure how many vents would need to be installed to accomplish this type of balancing. In addition, it seems risky to get an undersized boiler.

With regards to you and your friend's undersized boilers, could it be that your radiator vents don't vent properly, so you actually are reducing load in the same fashion that a thermostatically controlled vent would reduce load. Maybe this would allow your house to heat quickly and efficiently ( since you're heating enough of the radiators to support your heat loss requirements ). Just a random guess.

Another question. Does you/your friend's system have a boiler feed pump?

- Diar

Steamhead (in transit)

I was just about to check into that myself

We're looking at doing a 480 in a very large house on a VERY old Webster Type R system. Guess my next call is to the Power-Flame rep.

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John Cockerill

Are your pipes insulated?

Diar

Yes.

Diar

Let me know if you find a lo-hi-lo oil/gas burner for a 480 that I can easily get serviced on a residential oil/gas account.

Thanks,
Diar

mel rowe

Dijar, I've replaced almost all of my rad vents with TRV's; however, this did not noticeably change the % of time that my boiler operates, it just enabled me to get more uniform results throughout the house. I'm sure it had a beneficial effect on the boiler time and gas usage, but I haven't been able to determine how much. As for your second question- no we don't have feed pumps.If you have significantly improved the insulation and sealing of your house, I strongly believe you'll find that you need less boiler capacity than that calculated to fit the EDR of existing radiators.