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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.