LONG: Expected lifespan of a new condensing boiler?

kaismomDecember 27, 2012

We have to replace our failed Lennox CompleteHeat water heater that heats the entire house with 2 airhandler units and 3 zone in-floor radiant heating. The water heater also provided DHW. It was a 150K BTU unit which we think was over sized. We ran the water heater with 120F water temperature for years without any issues. We dropped the temp to give the failing Lennox increased life span :) The airhandler was fine at 120F even though the plumbers said it should be at 140F for comfort. (Never needed it)

The Lennox unit is dead. At this point, we have to decide how to replace this thing. When we initially got this, we were told that it would last 20 years. It lasted only 10 with multiple service calls.

We are being told that condensing boilers are replacement options and it will last 20 plus years. The reviews/articles I am reading from England (they have been used in Europe for decades) say that these boilers will last 10 to 15, not 20 years. I am inclined to go with shorter life expectancy, not the longer one being told by the local HVAC plumbers.

We have to use a side vent due to the house limitation. Chimney flue is not an option. I can't go with the cast iron conventional boiler at this point because of that.

We live in a mild climate (Seattle, WA) where
1. tankless water heater
2. power vented hot water tank
3. combi condensing boiler
4. condensing boilers with indirect hot water tank

are all viable options. Whatever we chose, the labor cost of rerouting plumbing will be about 3 days of labor with 2 guys working plus parts(pumps, expansion tanks etc) coming in at $6000 to $20,000 total bid.

My biggest concern is NOT energy efficiency since our energy bill is less than $1500 for the entire winter. (FWIW, the house is 68F or warmer with the gas fireplace running intermittantly and 2 1500W electric heaters placed in the house without any heat for about a week.)

My biggest concern is the longevity of the system with cost effective maintenance with the least initial up front investment. My analysis tells me that whatever system I go with, I will have a replacement cost in about 5 to 15 years, depending on the system. I will be extremely lucky to get beyond 15 years.

Those experts out theres, help me with the analysis.

There are couple contractors we elimated due to lack of 'good experience'. Everything I read tells me that the selection of contractors are more important than the selection of products.

How do you create a system so that when we swap out the boiler/heater next time, we minimize the labor cost?
Will the next system be a complete plumbing rebuld again?
What is a typical life span of a tankless water heater used to heat a house? (many are used in the city as such. Plumbers are saying 10 years. Is that true?) Are we really talking 5 years with a tankless?

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I don't have much experience, but was discussing this with our boiler sales rep the other day. He feels the tankless water heater setup is not as long lasting as a true boiler with hot water heating.

Hope this helps.

    Bookmark   December 27, 2012 at 10:56PM
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I would buy a 'real' furnance to heat your home - it should last easily 20 yrs without major repairs. Then buy a water heater for your hot water.

    Bookmark   December 28, 2012 at 10:16AM
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There is another possibility if you want longevity and low maintenance in a system. That would be geothermal. You also mentioned low up front cost, however, if you're facing replacement every 5 to 15 years, geothermal may also turn out to be the cheapest when you include life-cycle costs.

What are your electrical costs per kWhr?


Here is a link that might be useful: Carrier Geothermal

    Bookmark   December 28, 2012 at 10:23AM
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We are in a city with 5000sq ft of land with more than 1/2 built with garage and house. Geothermal is not physically possible.

Even if it was possible, our heating cost is very low, ie less than $1500/year. We do not need AC in Seattle. Let's say that you my heating bill by 50% ie $750 per year. The reality of getting 50% reduction in the heating bill is extremely optimistic. I live in a very HCOLA. I am hugely underestimating the cost of geothermal installation at $20,000. The numbers comeout to 26 year payback. The numbers I calculated is the best case scenario. Our electric rate is 7 cents per KW. I do a lot of cost analysis to see how to create cost effectiveness of my decisions.

The biggest unknown is the cost of maintenance which increases the actual cost of the system. When we installed our initial system, we were told 20 year life time. Well it barely made 1/2 of that. It makes a huge impact on the lifetime cost of the system when the appliances do not have real meaningful life time we can 'trust' and to make 'meaningful' calculations.

This has been the biggest stumbling block on many of my 'expectations' regarding energy savings; lifetime cost and maintenance cost. No matter where I use the money, if I have to use MY money to keep up the system, it is still costing ME money. At a certain point, I would rather spend more of MY money and pay higher energy bill if I can be guaranteed that the products work without the hassle of repair and replacement.

We cannot do a real furnace, ie traditional boiler with a flue, due to lack of space that can vent to the roof. That would require many thousands of modifications to the existing house to accomodate the flue. It is NOT possible.

Had I known that the lifetime of condensing water heater(which is what died on me) was 10 years instead of 20 at the time of installation, we COULD have put in a traditional boiler. Unfortunately, we were told 20 to 25 with a savings of energy! The experience from Europe (England mostly) is that the plumbers are telling their customers 10 years for condensing boilers....

This is what led us to remodel and get rid of the flue etc etc.

    Bookmark   December 28, 2012 at 3:06PM
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We have our geothermal HP for over 9 years now (10th heating season) and have never had a service contract or have ever needed service since it was install. The savings on service contracts alone will heat our home for 3 years. Maintenance cost should be little to none.

I would be very surprised if it was impossible to install a ground loop on your property. What makes you think this cannot be done?

Gas boiler will have a shorter life span than geothermal. After 20 to 30 years you may only have to replace a pump or compressor in a geo system. Even if you had to replace the whole HP the ground heat exchanger will be serviceable for longer than our combined life expectancies!

I'm not saying you should do it, I'm just suggesting that perhaps it is possible and that the numbers may work differently from what you presently believe.


    Bookmark   December 28, 2012 at 7:12PM
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