Before spending money on upgrading a 75-80% efficient boiler to a 90-95% efficient boiler, there may be better ways to save on heating costs, like insulation, which in an 80 year old house, prolly needs upgrading. Sealing cracks gaps and weatherstripping windows and doors will help more than you might imagine.

You mentioned condensing boilers, so I assume you have a hot water heating system (not steam).

Central air conditioning is better left as a separate system, as the load requirements for cooling are different than the load requirements for heating.

Indirect water heater is a nice option, especially if you have high demand for hot water.

Brewbeer -- thank you. I probably should consider insulation, but hate the thought of messing up the plaster walls. The attic & basement are insulated and we have Anderson thermopane windows throughout. Considering new fiberglass front door. The boiler (yes hot water) makes me nervous. Had to replace circulator pump last winter for many $$ on a cold night. Also chimney sweep recommended new lining for flue (heating mechanic said drafting is fine, etc.) New lining would be several thousand dollars. I think I would rather put money towards a direct vent boiler. I'm thinking I would reap the benefit of a new boiler while I am living in the house vs. replacing it in 10 years only to sell it to someone else. Lots to consider.

You are in the EXACT situation I am, except that my home is 25 years old.

As far as insulating goes: Get those light switch and outlet plate insulating foam pads. They can help block drafts through those openings and are CHEAP. A 10-pack of universal fit pads is about $1 to $2. I found them at Home Depot (top shelf above replacement switches and sockets in a clear and purple package). If your basement and attic are well insulated, you can put insulated siding on the house. And maybe even a vapor barrier. Just remember that the tighter you make the house, you need to provide controlled ventilation to keep the humidity and air quality in check. Too little ventilation leads to mold.

As far as the boilers go. My heating company showed me their line-up and had me choose three. They broke them down into a Good, Better, Best document. I researched the boilers, which included the latest-and-greatest Modulating boilers. (Modulating is their new buzz word.)

I couldn't find much to make me confident that the reliability of a modulating boiler (whereby the boiler can control its flame size) would be worth the risk of it going out when it's below zero.

I researched a boiler that wasn't on the Good, Better, Best list from the heating company. It's the Weil-McLain GV. The boiler is a 15+ year old design, 87.5% efficient. It's a condensing boiler. The heating company installed it for me almost two weeks ago. They installed it with an Outdoor Temperature Reset, which is a unit that adjusts the boiler water temperature in relation to the outdoor temperature. The boiler has been operating at 100F ~ 120°F so far because the temperature has been hovering around freezing.

The Outdoor Reset module saves you a lot of money because when it's 30°F outside, you don't NEED the boiler to run at 180°F water temperature. This boiler also goes cold when it's not needed. When a thermostat calls for it, the boiler can go to the set water temperature within a few minutes. Another energy saving because you don't need to store hot water when it's not needed. The Outdoor Reset module follows a calculated curve to set the water temperature. It has to be programmed for your climate and heat loss.

Speaking of heat loss: Definitely get a calculation done. With this, we found that the old boiler was more than double the BTU capacity! Holy waste of gas, Batman!

Our installer pre-programmed the boiler control module to work with an indirect water heater and even plumbed for it. Looking back (a whole week later), I would say that if you can afford it, get the hot water heater added on. This arrangement would allow you to use your old chimney passage for the new boiler. I didn't go that route and ended up having to have a new hole in the roof. Oh well.

My recommendation is to direct vent the boiler, which provides it with fresh intake air from the outside. We let ours use air from within the garage and this allows us to hear the combustion fan more. Once we get rid of our gas fired hot water heater, we can use the old flue as an air intake for the boiler, which will muffle its sound as well as keep our garage from being cooled by the air exchange.

With a condensing boiler you'll need a drain somewhat nearby. Our nearest drain was the washer drain opening. Since that's higher than the drain on the flu, we have a condensate pump normally used for an air conditioner. I don't know how often the pump runs, but the flu generates a lot of condensate so far.

So far I'm very pleased with this boiler. It's not on the bleeding edge of technology, so I don't feel like a guinea pig or beta tester.

Braytonak - Thank you for taking the time to share your insights & experience. Very helpful! I'll pick up those insulating foam pads this week. "modulating boiler" is a new term for me (next stop - google). If your temperatures are already hovering at freezing I'm guessing you are in Alaska or Canada. Thanks again!

Yeah, I'm in Anchorage, AK. And I forgot to touch on your question: Just as my heating company said, "Installing now will be more expensive than in the spring due to higher demand at this time of the year". Our scheduling delay was about 3 weeks.

The modulating boilers that I was shown were the Munchkin, which is built in the U.S. of a German design (if I remember right), and the Lochinvar Knight, which is a very upscale model. The Munchkin lives up to its name as it's very small. I couldn't find many good comments about it online due to reliability. I mean, really, who makes a boiler with a blower fan that literally flies to pieces? When looking at the Lochinvar, I found press releases but not much from owners. Maybe they're just too new, or they're rare?

Apparently the "Modulating" claim to fame is that the size of the flame is adjusted, thereby lowering the BTU output. Of course this must save a chunk of change, but I don't trust the reliability of it.

Our GV boiler seems to be doing well. It's Energy Star rated. When our Rater gave us the documentation on our house after our improvements, the boiler change alone was a HUGE impact (and should easily earn us a discount on our mortgage interest). The boiler is a bit larger than our old one, despite having half the BTU output, so check your measurements.

We lucked out with the gas bill, too. The gas company read our meter on the day the boiler was installed, so we'll have one solid month on our next bill with the new one. Wahoo!

Our total install price for this boiler was $8,657. I think the boiler costs (wholesale) around $2,500. The install took two people a day and a half to complete, leaving us without heat overnight, but this was just due to a minor complication with availability of parts from a store.

I don't have all the details as bratonak, but we replaced our boiler in the course of doing a remodel. Asked HVAC guy (this is Wash DC area) about high efficiency, and he recommended against it in our case. We too have 80 year old radiators, and the way he explained it was that in his experience with radiant heat the HE boilers don't reach their efficiency level because the temperature set point is not at the most efficient point. In other words, as he explained it, the boiler would be set to ~180, but a high efficiency boiler is most efficient at 220 (or 140, I forget). As a result, the actual efficiency would not be much better than a standard efficient boiler, and certainly would not be worth the extra cost.

Now, it's possible he was giving me a line, but I really didn't think so. He had no incentive to steer me to the cheaper boiler that involved less work. And your situation may be different. But it's worth asking whether you can expect to get the efficiency claimed before figuring on an actual 10 percent energy savings by spending for the HE boiler.

You may not have to mess up the plaster walls.

It's possible that the insulation can be installed from the outside, depending on the kind of exterior treatment you have.

one thing you have to be careful of, though, is if you have knob and tube wiring in the walls.

A high efficiency boiler does have a sweet spot, which is mostly during the fall and spring when it can run at lower temperatures. This only makes sense because you're having to heat the water less. Radiant heat normally runs at 180°F. It's possible that the boiler would overheat to 200°F or more, which is why there's supposed to be a secondary shut-off control.

My system has been running at around 120° lately, which takes longer to heat the house from a lower temperature, but is more efficient when the house can be kept stable. It's programmed to peak at 180°F at 10°F outdoor temperature or lower. (I set the thermostat to 70°F.)

You didn't mention what type of radiators you have. Huge cast iron units, simple baseboards or in-floor radiant?

When you replace the boiler, you might choose to replace the thermostat with an electronic one. I've read that using those temperature change schedules on them is actually counter-productive with radiant heat. It takes so long to recover from a temperature drop that you'll expend more energy recovering. I can't recall where I read this online, but it makes sense to me. I programmed my thermostats to stay at the same temperature all the time.

All your comments are very helpful. Hopefully I will sound knowlegeable when dealing with HVAC suppliers & installers. Good point to question whether or nor HE boiler is even practical with my large cast iron radiators. Unfortunately, adding insulation from the exterior is not an option, as I have a stucco house. I do have an electronic thermostat. Winter 05/06 - I went with varying temperature settings based on need. Last winter 06/07 - I kept it set continuously at 68, after also reading up & down adjustments were energy wasting (made sense to me too). Didn't notice a significant cost difference but to be honest I didn't closely monitor the number of gas therms used each year (& last winter in NY was relatively mild). Thanks again for all the thoughtful comments.