View Full Version : Effiency Savings??
07-06-2010, 04:27 PM
Hi guys, I am new to the forum- and boilers in general. I am in the process of buying a home with a gas fired boiler. The only thing I remember about it is that it was installed in 1963, and it has 3 zones. The house is 5500sqft all appliances are gas. The gas bill is close to $6K a year. The electric is not very much more than what I pay now and its a much larger home (both have central AC). I am guessing either the house stays cool, or the boiler is just so inefficent that it is burning money. I did notice the people that live in it now have it on in the summer- the temp guage read around 180 deg. How much of a difference will a new effiecent boiler make, also shouldnt I turn it off in the spring/summer? It seems like it would cost alot to keep that water warm all year round. It has a separate water heater. Any input would greatly be appreciated. Thanks in advance!
07-06-2010, 07:12 PM
Are you sure the WH is not an indirect? This is a tank that is heated by the boiler, not an internal burner. If it isn't an indirect, then yes, you can turn it off in the summer.
Depending on the system you have and how it was installed, a new boiler might save you a fair amount. Back then, the boilers often were way oversized. So, the first thing you need to do is do a heat loss cal to see what size boiler you really need. A condensing, modulating boiler with an outside reset would likely get you a tax credit and/or a rebate from your utility or state.
07-06-2010, 07:32 PM
Thanks for your quick resonce. I am assuming its a boiler. It has a 3 B&G valves then a large tank. The home inspector said it was an expansion tank but it looked like a large holding tank? It didnt look like a expansion tank because it was large. Maybe I can get some pics of it. How do I calculate heat loss? Judging its a very old house that was originally a carriage house I am not sure how well its insulated.
07-06-2010, 07:33 PM
How do you find out about tax credits/rebates in PA? Thanks again!
07-06-2010, 07:41 PM
I just re-read your post. The water heater is completely separate. Its not plumbed into the boiler.
07-07-2010, 10:19 AM
There are federal tax credits available for 30% of hardware costs up to $1500 but you must meet certain efficiency requirements to qualify. call your local utility company to see if they are offering any rebates on equipment. They, along with the gas association, are often giving rebates on new, efficient equipment. A few years ago, I got $1100 back for a new boiler and indirect WH. Some states do rebates as well. A google search may turn up things.
There are some on-line manual j or heat loss analysis spreadsheets. They require imputs of size, orientation, size of windows, insulation, etc. to get a good result.
When I upgraded my boiler (a Buderus mod-con 142 series if I remember correctly), my gas bill dropped a bit more than 1/3. My old one wasn't that inefficient, either.
07-07-2010, 12:30 PM
I looked at the boiler today. It's a old American Standard. It looks like it has a newer gas valve in it. It says 600k BTU in 480k BTU out. Do I divide to figure out efficiency of the boiler?
07-07-2010, 12:38 PM
That's best case, and if it is oversized, it will never reach best case, but yes, output/input gives the relative efficiency. There's more to total system efficiency than that.
07-11-2010, 07:06 AM
I'll bet it's twice as large as it needs to be to heat the house. Get a heating professional in there to do a load calculation. Either a total heat loss or they can count up the baseboards or radiators. Total loss would be better but the radiation is what it is. A Buderus or similar high efficiency boiler with outdoor reset control should wach that bill down by 30% minimum. I think that 47 years is a pretty good run for that old boiler.
Using the input/output numbers only gives you the steady-state 100% duty cycle (always burning) thermal efficiency of the beast. The operainging efficiency will be a function of it's duty cycle & standby losses when not burning. I'm bettin' 480KBTU/hr is more than 3x oversized for almost any 5500' house in PA unless this house has zero insulation and is as drafty as a chicken coop, which would also explain a greater than $1/ft^2 of floor area gas bill in a place with a ~6000HDD climate. (My house is by no means super-tight or superinsulated, and we're spending ~$0.50/ft^2 per year for heat & hot water in a ~7000HDD climate with a ~82% efficient boiler.) Yours would probably have run ~75% efficiency (AFUE) in 1963 had it been ideally sized for the peak coldest-hours-of-the-season load, but if 3x+ oversized it would have been closer to 60% "as operated" back then, and probably 45-50% now. Simply dropping a "right sized" modulating condensing boiler in it's stead would roughly double the efficiency- halve the operating cost(!).
If you buy into a high efficiency condensing gas boiler (and you should), consider installing an indirect-fired tank hot water heater at the same time (which will also have an associated subsidy.) Using the same boiler for both heat & hot water will increase the operating duty cycle, for a higher AFUE, and lower the air-infiltration heat losses to the house by getting rid of yet another open flue (== a hole in the building envelope drafting 24/365.) If the hot water heater is sharing a chimney flue with the boiler this is even more important, since the flue will be many times oversized for the output of a standalone HW heater by itself, and the chimney will self destruct from the inside out over several years due to the condensation of the hot water heater's exhaust, and may present a serious backdrafting hazard. (google "orphaned hot water heater")
If your heat load is large enough (and it might be), going with the Freewatt (http://www.freewatt.com/products.asp?id=172&name=Hyd) cogeneration system that uses the waste heat from a small generator to support the heat & hot water loads in association with a condensing boiler (a boiler too big for my house, but probably not yours), would likely have the biggest return on investmen, even though it's significantly more expensive than just a condensing boiler + indirect HW heater option, since your electric bill basically goes away for 6-8 months of a year (unless you're a real power-pig with 8 computers and 3 TIVOs running 24/365 :-) ). I talked a guy in my office into replacing his antique boiler in a 6k foot house with a Freewatt 3 heating seasons ago, and even though it was close to $20K, as a system it has already paid for itself (!). He is seeing a ~45-50% reduction in annual gas use, and with net-metering is clocking ~6000kwh off the electric bill.
But if the cogeneration system is not available in your area, there are many good mod-con boilers out there (I like Triangle Tube Solos, myself, but I'm not a zealot.) Just be sure whichever boiler you buy is well supported by the distributor. In fact, calling the distributor can be a good way of finding a competent installer- they know who the bozos vs. real-deals are, who installs the most, and has the fewest support issues with the product. Also very important: be sure that the installer does a "Manual-J" type heat loss calculation to come up with the right boiler size, and don't oversize it by more than 15%. Most heat loss calculation software overshoots reality by 20-30% already, so going any larger just pushes you further DOWN the efficiency tree. With modulating condensing boilers though, the more important number is the MINIMUM modulated output (so long as it's max is around or above your design-day peak), since that is an ultimately limiting factor on it's duty-cycle. Remember, longer burns==higher efficiency. Only at 100% duty cycle does the efficiency of the boiler achieve it's rated thermal efficiency.
It's highly unlikely that you NEED 180F water (even on "design day", the coldest 1-3% of hours in a heating season), no matter what type of radiation you have. A proper installation of a high efficiency boiler will include some tweaking of the control curves that adjust boiler output temp in response to outdoor air temp (aka "outdoor reset" control, built into most high efficiency boilers.) The thermal efficiency of a condensing boiler increases as it's operating temp decreases (or really the temperature of the return water from the radiators going into the boiler), and the effect is pretty dramatic for every 10F you can drop it below ~130F, which allows burner exhaust to condense on the heat exchangers in the boiler, climbing into the 90s for efficiency. At 180F out, 150F back even a condensing boiler is only hitting the mid-80s, but at 130F out, 110F back you're in the low 90s. If that's delivering enough heat, that's where you want to run it (or lower.)
Even if your current boiler is grotesquely oversized, any house that's burning $6K/year in gas would do well to have a professional energy assessment done that includes both pressure-door testing and thermal imaging. It might be as much a $500 just for the testing, but finding & fixing all of the air leaks & gaps in the existing insulation is usually cheap (and subsidised) with a HUGE payback in both dollar & comfort terms. Often insulation contractors who offer air-sealing services will do the assessment for cheap/free as part of the package, and will verify the reduction in passive air flow into/out-of the house. Since this step might affect the boiler sizing, it may be important to go there first.