AFUE Most Efficient Air Supply Source

[Deleted User]

Heating a large, old, poorly insulated 3-story house with 12-yr old Weil-Mclain gas-fired atmospheric standing pilot boiler (#EG-75)& hydronic standing iron heat distribution, intermittent BG circulator operation, cold start. No auto reset; no flue damper. The 300,000 Btu/hr input may be over capacity; no good heat-loss study done. (Climate Zone: Philadelphia). Hard to add insulation; stucco-plaster walls, no space to insert; many leaky windows, storms old type, not tight and much too wide a gap. Any data I did not supply? Ask me.

Question: For max. efficiency should combustion air come from the large basement (which gets QUITE warm)or should cold outside air be fed to boiler by opening window in boiler room and closing door to rest of bsmt.?

If you suggest using air from bsement, with window kept closed, should door to main floor be open to allow that warm air to come up & heat the living space?

Question: Any other suggestions to save fuel? (Last year one month was over $800--at 66 degrees.)

Question: If replace boiler--solely to save money, it runs fine, burns clean, gives even temp (but 2d floor cooler than 1st and little used 3d floor is cold, but that's okay)--what type, models, attachments (auto-reset, flue-damper, etc.) do you suggest? (Contractor I have asked says it is fine, no big improvement available, does not like condensing with hydronic.)

THANKS TO ALL.

Unknown

Mike are you a

homeowner? I assume you are but want to make sure.

1. You definetly need to have a heat loss done. Someopne needs to do an energy audit for you. Check with your local utility for contractors who do this along with boiler installs.

2. Air for combustion is a very critical item that needs to be determined by a professional. Opening windows and doors can be the worst thing you could do as you will create a possible pressure difference in the area causing spillage of flue gases into the room. Proper control of combustion air is something that must be done professionally.The end result of tampering with air flow can be possibly having carbon monoxide produced.

3. I suggest you look at getting another contractor. If you are looking for a more efficient package there are plenty available.

4. As much as you can also look to add insulation and perhaps new windows.

DaveGateway

While insulating might be tough

You got try to replace windows/doors and maybe add some insulation to attic. There's realy no point in trying to fix or replace the boiler if the house has a huge draft problem. If you're spending over $800/month just to heat the place, I'd get an equity loan and get some of these issues fixed first.

Constantin

Some Answers...

The local utility can tell you exactly how much heat loss your house is experiencing via your gas bills. Given the location and the efficiency of the old heating equipment, it is trivial to back out the number of BTU's the house is losing at any given time. I have included a sample spreadsheet to help you with this. According to Cornell's library of heating degree-data, Philly has 4954 HDD per year.

Instead of ripping out windows wholesale, I'd go the economical route and retrofit ultra-efficient storm windows from Harvey (Tru-Channel). Those storms will cut down infiltration a great deal. Next, get insulation into the walls. Either open-cell foam or dense-packed cellulose have excellent infiltration resistance and can be retrofit from the inside with only minimal holes in the walls.

If you pipe air directly to a boiler, you simply reduce the amount of infltration a house will experience. IMHO, this is a good thing. However, be sure that your boiler will be happy doing sealed combustion - some manufacturers don't like it because they're afraid that cold, damp exterior air may cause condensation inside the burner.

Before replacing the boiler, I would insulate and weatherize the house. Your money will be better spent there. However, also have someone come in and take a look at the system. You may have a control issue on your hands if the various parts of your home are at significantly different temperatures. With large cast iron rads, you may be well off with a condensing boiler in the future.

Chuckles_2

re the spreadsheet

I suspect you have misunderstood the I=B=R issue. Given a certain theoretical heat loss estimated from windows and walls, the derating is supposed to cover the fact that there may be losses in the process of getting the heat from the boiler to the living area. However, if your spreadsheet starts from actual therms consumed (from past bills), this already includes the losses (as experimentally determined), which are the same for the old and new boiler.

In other words, if you add 15% to the bottom line (boiler size needed), you have to subtract 15% fom the top line (therms actually consumed).

Also the annual therm usage includes the baseline: gas used in cooking, drying and hot water. This should not go into the sizing of the boiler. For example, our house used about 1800 therms last season, but 300 of those were baseline, so ignoring it introduces a 17% error. One way to reduce the error is to use the January/February bill and degree-days rather than the annual usage and degree-days, since the baseline is only a small part of the peak winter bill. Last January we used 325 therms, of which about 25 were baseline (8%). One way to determine the baseline is from summer usage.

Finally, you have to use the actual degree-days for the year for which the actual therms are used in the spreadsheet. Degree-days vary 20-25% from year to year and the average is not good enough. Your spreadsheet doesn't give explicit instructions, but in your post you suggested looking up degree-days in the Cornell library...no good. In our area the monthly gas bill gives the month's actual degree-days; wunderground.com also has historical data.

PS I haven't even mentioned whether the AFUE is a good way to estimate actual efficiency.

Plumbob

how big is your house?

>The 300,000 Btu/hr

> input may be over capacity; no good heat-loss

> study done. (Climate Zone: Philadelphia).


You can do your own "heat loss" easily if you have your January '04 bill. Many gas bills include the billing cycle's degree days, or you can look up hitorical data on wunderground.com. Divide the therms by the degree-days, multiply by 270,000. That's the size boiler you should have, in BTU/hr (explanation: 24 hrs in a day, 100,000 BTU in a therm, guessing 65 degree-days in a design day in Philly, so 65*100,000/24~=~270,000).

> Any data I did not supply? Ask me.


How many sq ft is the house? That would give people a sense of whether your gas bills are reasonable or way out of line. Maybe you have a Bill Gates type mansion; we don't know. A ballpark number to shoot for in an old house is 10 BTU per sq ft per degree-day. 10-15 is not ideal but not necessarily worth fixing; >15 and you've got problems. (New construction is generally less than 5.)

> Question: For max.

> efficiency should combustion air come from the

> large basement (which gets QUITE warm)or should

> cold outside air be fed to boiler by opening

> window in boiler room and closing door to rest of

> bsmt.?


Opening a window makes no sense at all. In a leaky house, taking air from the basement is fine. But why is the basement getting so warm? That's one thing to fix.

>

> Question: Any other

> suggestions to save fuel? (Last year one month

> was over $800--at 66 degrees.)


if "large house" means 3500 sq ft, you've got problems, and it is hard to identify them from a distance. If it means 20,000 sq ft, maybe you are fine. Quoting prices ("$800") and the calendar period ("last month") doesn't help, since the price of nat gas varies and the weather varies with location. How many therms were consumed, and how many degree-days were there in that billing period?

> Question: If

> replace boiler--solely to save money, it runs

> fine, burns clean, gives even temp (but 2d floor


The boiler itself should be fine. It is not clear if it was installed properly.

> cooler than 1st and little used 3d floor is cold,


This may just be a matter of turning the water pressure up to ~18psi.

> (Contractor I have asked says it is fine, no big

> improvement available, does not like condensing

> with hydronic.)


"I don't like condensing hydronic boilers" is contractor language for "I don't know anything about condensing boilers but I don't want to admit it". But anyway, you probably don't need a new boiler.

PS Do you have adequate attic insulation? That's usually the most easy and cost-effctive insulation to add.

Plumbob

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