Has she changed the air filter in recent memory?
My best guess is that there is a blocked or clogged sewer vent. When the heater's return fan kicks in High the negative pressure is enough to draw fumes back through a sink or toilet trap.
If you smell sewage, always check the traps and vents first.
She bought John Wayne Gacy's old house.
There are way to prevent back flows. (back flow preventer)
Consult a plumber.
Other than that, I can't imagine what it could be. Raising the temperature probable causes the air handler to run more, which brings in more gas.
If the smell is coming out of the heating vents, I would check the ductwork for the presence of standing water that could have leaked in and gotten stagnant.
If the smell can't truly be traced to the heating vents it may actually be sewage. I would check the plumbing fixture drains (commodes, sinks, shower/bath, etc.).
Good Luck!
Another great place for sewage odor to come in is the washer drain.
The solution is to crack a window
Is she logged on?
If the unit is ground level, she may have also been experiencing water seepage on the floor. Units in the attic will drip water onto the ceiling (clues that lead to this point).
What do you mean 'central heating (no gas)'? Do you mean that it has an electric element to heat up the air as opposed to gas? Or that heat is supplied from a 'central heating unit' source that services several homes/buildings and she has a smaller unit that she can turn on to draw some heat from that central source as she needs to? And what is the significance of '65 degrees'? Are you saying that with it running below 65 degrees, there is no smell when the heat comes on? There is some missing information here that would be useful to a troubleshooter.
My guess is that some of the posts here that speak about the issue of sewer gas are on the right track..... but they did not go far enough in the explanation. If your cousin has a sink, toilet or more likely a shower in the house that does not get used very often, what can happen is that the u-tube trap in the drain line can dry out. If used regularly, the trap should have water in it - this is what will seal from the back flow of odours and gases up from the sewer. However, if the shower does not get used for a few weeks, the trap may dry out and thus create a ready path for fumes. If this is the case, it means that your cousin's heating unit has the supply and return ducts connected in such a way that the entire house goes under negative pressure when it comes on.... something that it should not do but quite often happens because contractors don't understand the concept of make-up air. [By the way, the same thing could happen if all the bathroom exhaust vents, kitchen range hood exhaust, central vac and so forth are also on at the same time - the house goes to negative pressure since all these devices are exhausting at the same time that no devices are bringing air in to replace what is being taken out... hence house goes slightly negative. This can be a very dangerous situation under some circumstances. If it is a very tight house which allows it to go negative and there ARE gas appliances in the house such as a water heater or a furnace, there is a serious potential for gas fumes to exhaust into the house - trust me on this, more than one person has died of carbon monoxide poisoning with this as the cause.]
Signed,
retired Building Maintenance Mechanic with a HVAC background :>}
Next if could possibly be a dead mouse in the ventilation system but that doesn't smell like sewer IMO.
Since this is a central heating thread.... :)
I try to turn the thermostat down at night to save energy (and money). But this old house has some leaks, and the temperature drops fast inside the house.
So, the unit seems to cut on and off just as many times during the night when it's set on 63 degrees compared to when it's set on 72 degrees during the day.
Seems to me there is no benefit in cutting it down if it's going to run just as much as normal. I might as well leave it on 72 and be comfortable.
Is that right? Any heater guys out there who can answer?
Thanks in advance!
(And just as a side note, I have fixed what leaks I could by adding sealing tape, etc.)
Dead rat in the system vents maybe. I have seen that before.