Old Smith Boiler G-12 vs New?

Dennis Fedele

Hi,

I have a few questions below.

I currently have a Smith G-12 serial no. 2989 propane gas hot water boiler heating approximately 5500 square feet on 5 zones (5 apartments and a laundry room). Can you help me understand the age and efficiency rating of this furnace. The plate says input 252,000 output 201,000 and net IBR 175,000. (The numbers are approximate as it was difficult to read).

There are a few times in the season when the zones are competing for heat. Some apartments are very hot while others are struggling to stay warm. I installed all new windows and doors and fully insulated the attic. This made a substantial improvement but did not solve the problem. Could the boiler unit be undersized? I wish to add 1 more zone to control the laundry room separate from the apartments and this would continue to heat the same amount of space just six zones rather than five, is this practical given the boilers size?

How does the efficiency rating of the G-12 compare to the Smith GB250-6 propane which has similar input and output ratings?

I will be reviewing some proposals to replace and modify this system later this week. The contractors will be proposing new Smith furnaces among others. I appreciate any information you may provide me. I cannot pretend to understand how to size a furnace but my guess is that I should have a GB250-8 based upon the heating capacity rating of 280 MBH - am I even close? Can I expect savings on my energy bills by having a more correctly sized furnace (if this is my problem)? What could I expect in energy savings %?

Sincerely
Dennis Fedele
Milford, NH

John Mills_3

HELP HIM!

I referred Dennis to this board figuring one of you wetheads could help him. I could suggest he take out the boiler and put in forced air

Boilerpro_3

Some starting points

Number one, is that a full heat loss calculation using good practices should be made. This will get you a starting point for equipment sizing.

Your problem of some zones overheating in cold weather and others not getting enough heat could be a simple balancing problem...too much water flow to some areas and not enough to others. Overheating should not occur if the controls are operating properly and the system is piped correctly.

Undersized boilers are extremely rare in my parts (northern Illinois). Since apartment structures have so many people in them generating heat, usually even a greatly undersized boiler will heat just fine. The boiler size you currently have could easily heat a 10,000 sq. ft. church, however it all needs to be based on the heat loss calculations.

I am not familiar with your existing or the replacement boilers you are looking at, so I can't say much about efficiency. What you my want to explore is piping in a small high efficiency boiler (90%+) next to the existing boiler (if it is in decent condition). This new smaller boiler would run first whenever heat was needed in the structure, with the old boiler staying off except on the few coldest days of the year. You get the advantages of high efficiency and have built in backup for when the new boiler fails midwinter. You could also tie your water heating (a very large chunck of you fuel bill for most apratment structures) back into this high efficiency boiler using an indirect fired water heater.

Installing multiple furnaces, in my opinion would be a mistake. You would be installing five pieces of equipment to maintain in addition to water heater(s) and have replacements every 12 to 15 years, versus maintaining one or two boilers that need replacement every 30 to 40 years.

As to dealing with the age old tenant abuse of heating (thermostat set at 80F with windows open), an outdoor reset control could be installed that will limit the heat available to the tenants depending on outdoor temperature. If it is warm out, there would only be a little heat available, if it was cold , more heat would be available. If a tenant leaves a window open they will get cold, because the heat they can get is limited based on how cold it is outside. If they turn thier thermostat to 85, usually all they will get is about 75.



Boilerpro