Boiler vs. 90% Furnace

Old 10-19-09, 10:07 AM
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Boiler vs. 90% Furnace

We live in an old house with old fashioned radiant heat. We have the old radiators all around the house (1 story w/ basement). We would like to add central AC. This would involve the AC equipment (and duct work) as well as an air handler, or furnace.

I am now thinking that it may be best ( we will only live here for maybe 10 more yrs) to dump the radiant heat altogether and go with a nice new super high effecency furnace. I think it would kill several birds with one stone.

The current boiler is in good shape, but it is not very effecent (reading its tag). It is naturally aspirated using room air for combustion. This depressurizes the house and if we have a fire in the fireplace the smoke will be drawn in. I think the new furnace will be fed with outside air thus elimanating the de pressurizing problem.

Also, our radiators are in the way of some remodeling we want to do. I'd have to move and repipe them, but the pipeing is 90 yrs old... so it would likely all be replaced at that point. Very expensive job.

We will be running ductwork for AC anyway (basement is clear and it won't be very difficult at all), so why just buy an air handler... why not spend some more and get a new, state of the art, condensing, forced air furnace instead and run that.

It seems like that is the best route to go...

Is there any way to compare gas useage of our current boiler and a new 90%+ furnace?
Old 10-19-09, 11:50 AM
Join Date: Oct 2008
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If nothing else were to change, an 80% boiler that uses $3000 worth of fuel per year would use $2666 if it were replaced by a 90% boiler. (.8/.9) times the yearly fuel cost or units. So in theory you would not have recovered the cost of conversion when you sell and would be selling with a furnace that is now 10 years old and probably a bit behind the times compared to newer units at that time. But 90 year old pipes would scare me and you have the opportunity to combine the upgrade with the new ac system so your thinking is good. Just for options, you might want to read up on small duct high velocity HVAC systems. They work especially well for retrofit projects and might allow you to minimize the loss of space in your basement. The numbers at the top were based upon all else remaining the same, which will not happen. One of the issues that comes up is what size system do you install, the one that fits your current house or the one that would fit after improvements. The smaller units, both heat and ac, are less expensive and more efficient when sized right. A good approach is to start with some air sealing and added insulation. Then have a manual J heat loss done to correctly size the system. The combination of insulation and a new properly sized system then has not only a better payback but is more attractive when sold.

If you want more advice on insulation, we can help.


Last edited by Bud9051; 10-19-09 at 11:51 AM. Reason: corrections
Old 10-23-09, 12:38 PM
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If you haven't made up your mind yet there is another option.

Living in New England, I grew up in MA, hot water heat is a nice feature. It has a nice even temperature feel to it. My mother always complained that when they moved into their new house, with forced hot air, that it would be hot then cold.

I think you'll find running conventional ducting to be very expensive and take up some closet or other spaces.

Have you considered a mini split system for just the a/c? They are small. You'll only have to run a couple of refrigerant pipes and power to the indoor unit. You can usually run a couple of units off the same outdoor unit. This might be a reasonable idea if your house is fairly open. You could put a unit in the living room and another in your bedroom for example.

High velocity systems, like Bud says, are another good choice, if you decide to redo the entire system.

No matter what, make sure you've done all you can to tighten up the house. Get an energy audit to help find those areas that are not well insulated, very common in an older home. I think that'd pay off quicker than the new system.

As to the fireplace, most of them are more effective at pulling heat out of the house than actually producing it. You can retrofit that with an outside air vent, or open a window near it, just a bit.

good luck.
Old 10-26-09, 04:31 AM
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My house is a small 1 story with a pretty open basement. There isn't much in the way of running the duct work, which I will do myself, and I don't think it'll take up any room really. The large duct runs will basically replace the low hanging pipes of the boiler system. Actually, by removing the radiators from the house it will free up ALOT of room and allow us to do some remodeling.

We do like HW heat better, I grew up with it, but since this isn't our final house I don't want to get to elaborate with the system. Those mini splits and high velocity and other "new" systems are still fairly expensive as far as I can tell. I think that by replacing the entire system with new standard high effecency equipment it will be best in the long run.

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