Gas heating/ heat pump air conditioning
I am not an expert on Air Conditioning but I would like to add my post to help those who fall into the realm of general understanding in how your heat pump combo gas furnace work together. Very reliable system whatever name brand you have and can be forgiving on the pocket book if thermostat discipline is enforced and maintenance is taken care of. Don’t move your thermostat to much. Major bill in gas throughout winter and electric in summer if you move it up and down. Don’t do that. Some of these tips will help in other systems also- lets prepare for the real heat and humidity.
First, preventative measures are needed to ensure that maximum life is achieved for this mechanical device. Here are some tips from personal experience.
#1, replace any washable style filters right away. Measure them for replacement then throw them away. (see jpg1) It is imposes future problems with your system. It is very porous and the accumulative matter can and will creep through this wide of material. The collection will occur on the evaporator coil webs over time and freeze up the system, this is the first symptom of sick air flow. Replace it with a medium ranged filter, my best advice here. CHECK it every week.
#2, The gas fired heat and exhaust fumes are hitting your evaporator coil in the winter. Thus welding on foreign matter on the fins that cannot be easily removed without caustic solvents or just plain galvanic removal, which never happens so you have to have completely have new
installed. This is a forced air system, evaporator coils in top part. (see jpg2)
#3 Watch your lines. If you see water or ice on either one of them the balance is off, It’s all about balancing your homes environment by evaporating the moister out of the air, and most impertinently draining the moisture to a properly approved place. Watch your secondary means, the low point of water access, for condensation.(see jpg3)
Prota-
Replies
If your combustion exhaust fumes are hitting your evaporator coil, your system is not installed correctly. The gas fired combustion is inside a heat exchanger, and then to a flue and out. No fumes should be mixing with air handler air. Paul
Can you connect a water heater to a combo units type B venting system in an off gas situation like this and be safe? Just asking and thank you. ;)
Not sure I follow what combo you are referring to. I have a hot water coil heat exchanger in one of my central forced air systems. The hot water is from a gas water heater located in a basement utility room with its own air supply. The air handler is in the envelope of house air, so there is no negative pressure created by the water heater exhaust. The water coil heat is cheaper than the heat pump heat, and warmer/faster than HP. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Do you mean: can you connect a gas water heater vent to the B-vent flue of a combo heat-pump gas backup furnace?
As long as it is "Y'd" and not "T'd" I can't think of any reason ypu coludn't.
The water heater alone is venting through that combined flue in the warmer months, and, if sized properly is ok. There is more natural draft during cold weather so the water heater flues gas alone (when the gas back-up isn't being fired) should do OK.
OTOH, I've never tested the draft on such a system (I've only seen 2 or 3 like that) so the above is just a bit better than an educated SWAG.
"Do you mean: can you connect a gas water heater vent to the B-vent flue of a combo heat-pump gas backup furnace?
As long as it is "Y'd" and not "T'd" I can't think of any reason ypu coludn't.
The water heater alone is venting through that combined flue in the warmer months, and, if sized properly is ok. There is more natural draft during cold weather so the water heater flues gas alone (when the gas back-up isn't being fired) should do OK.
OTOH, I've never tested the draft on such a system (I've only seen 2 or 3 like that) so the above is just a bit better than an educated SWAG. "
Are you saying that you have only seen a 2 or 3 installations where a WH and gas furnace share flue? I thought that was very, very common. I don't see all of the house that you do, but in the 1/2 dozen that I cna think of they are all like that.
Or are you saying that you have only see a few that are combined with a heat pump? But the heat pump really does not have anything to do with the venting of the gas furnace and WH.
I have only see a few that are combining a heat pump with a gas fired backup.
Most of the heat pumps in my area (which aren't that many to start with) use electric as the backup heat source, but I have seen a few where the back up to the heat punp was gas fired.
And you're right, gas furnace/water heater sharing a flue are very common and if installed correctly, work fine.
The amount of heat being run through the flue can affect its performance, however, which is why I'm hedging my bets here.
For example: in my area (NW Ohio) if we change fromn a lower efficiency natural draft furnace to an 80+, and are runnning both the water heater and furnace into an chimney on an exterior wall, we have to reline the chimney with metal flue because of the lowered amount of heat and increased chance of condenstaion within the original flue.
Interior chimneys don't usually need that relining, although several HVAC companies in my area reline the interior chimneys as well.
That's why he needs to get further evaluation oif his particular situation - we don't know enough about his loca conditions and current set-up.
It's posssible that the water heater may need to be separately ventedf.
As Paul mentioned, if "exhaust fumes are hitting your evaporator coil in the winter" you have a major problem and should immediately disable the furnace.
The gas fumes (aka combustion gases) should be contained inside the heat exchanger and flue; if they are mixing into the air being moved through the evaporator you have a potentially killer carbon monoxide problem.
(That is one of several reasons a return is not allowed within 10' of the furnace - if there is backdrafting, the backdrafted flue gases could more readily mix with the air circulated through the house. There are other reasons, having to do with pressure zones, as well.)
Paul, wadda ya tink?
Edited 5/25/2004 10:51 pm ET by Bob Walker