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My sister has a large Victorian house, circa 1810 or thereabouts. Needs a new furnace. Getting differing opinions. Ceilings are 12ft. high. Upstairs 3 brms., each room has a heat vent but no cold air returns. There’s only one in the hallway connecting these 3 rooms. Couple people said high efficiency is the best. Others said no, you won’t like the cold air that blows out before the heat part kicks in, and even then the air doesn’t really feel warm because it’s not much higher than our body temp. (This sounds familiar somehow). There’s the exact reason why I really dislike my 90% efficient one. (Insert forgotten explanation about combusting gases (?) here). Others said those things only really work in new build houses ‘cuz they’re so air tight – nothing at all like the drafty houses of 1810, or the ’60’s, for that matter! (mine). She’s told she’d probably be happier with a lower efficient furnace – might cost a little more bill-wise, but would get warmer heat and feel a lot more comfortable. (She loves the fact that you can stand over her heat registers and get heat like from a hairdryer set on hot).
Anyway, anyone familiar enough to offer suggestions?
Oh, BTW, one guy told her since there’s no cold air returns in the upstairs bedrooms, and the rooms are carpeted such that closing the doors seal them off pretty good, she’d have to cut about 2″ off the bottom of the door to let the hot air circulate because the room is pressurized and the heat has nowhere to go. At least that’s the best paraphrasing I can do.
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Weird. I've never heard that the temp. rise across the exchanger in a high-efficiency is much different from a mid-efficiency ... a function of cfm from the air handler. There is a maximum temp. differential that the exchanger can safely handle without cracking, perhaps this is different in the very expensive stainless exchangers in the high-efficiency units. Cold air from registers is the complaint I hear leveled at heat pumps.
The main difference between mid- and high- is that the 80%+ AFUE furnaces condense out the combustion moisture to reclaim the steam energy in it. This can cause problems if not properly handled because the condensate is corrosive. But the HVAC guys I've talked to around here (VA) seem to feel they've worked out the problems of the early units. Our 78 is fine for us ... we don't need all that much heat so the payback for replacing it would be forever+.
Always looking for more info...
ANYWAY, rather than mutilate the doors cut holes in opposite sides on a stud bay, one high and the other low, to permit air to return. This suggestion came from Freddy Lu ... looks better and transmits less sound. Or consider alterntives to forced air ... radiant etc ... avoiding all the uneven pressurization problems of forced air, esp. in leaky older houses ... like ours.
*Adrianne. An energy efficient--tightly sealed, heavily insulated-house is more important than an energy efficient furnace. What? you say.If the old clunker needs replacing, do so. But don't think you will se a major difference. This is a painful lesson many thousands learned during the OPEC crisis. The efficiency of a furnace is a function of the house's efficiiency. The house isn't going to leak less because of a high efficiency furnace. GeneL.
*Adrianne;What a crock. If the house is inefficient, and looses heat, why throw more money away with a low efficiency furnace? Keep in mind that an 80% will cost 20 percent more to run than a 96%. My perception is that the higher efficiency units are better quality units also, but just a perception.(A pet peeve is the costs. If a unit costs $1000 more, why does the HVAC guy want $2000 to add it to the job? Same duct work, etc, no?)You may check and see if they can wire the unit to always come on with the high demand (for that hairdryer feeling). It does lower the overall efficiency, but not much. I actually never notice the difference (thermally) between the two modes, but then again I live in a new home.Actually every morning the kids fight to see who gets to drink their OJ while camped over the bigger of the two floor registers in the dining room. Nice and warm.Don't forget to address the ductwork no mater which efficiency you choose. You can throw away major bucks with minor leaks and un-insulated ducts.The door business is true, but perhaps not 2 inches. Also, how often are the doors closed? If it is alot, you may need to trim them, otherwise keep 'em open and get everything warmed up.
*One comment the poster received was: "Others said those things only really work in new build houses 'cuz they're so air tight - nothing at all like the drafty houses of 1810, or the '60's, for that matter! (mine)."I think what Gene meant was don't put a 21st century furnace in a 19th (barely!) century house and expect miracles. Fix the house first. No returns, for example is a BIG problem. You may even find that a lower efficiency furnace then saves you money if the heating season is relatively short. It would take a loooong time to recoup $1000 in energy costs here in VA by upping the AFUE a few points. Higher AFUE units have had a greater incidence of problems because of their greater sophistication and the corrosiveness of the condensate, though at least one HVAC guy I talked to said they'd improved a lot recently.